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rfc:rfc5545

Network Working Group B. Desruisseaux, Ed. Request for Comments: 5545 Oracle Obsoletes: 2445 September 2009 Category: Standards Track

   Internet Calendaring and Scheduling Core Object Specification
                            (iCalendar)

Abstract

This document defines the iCalendar data format for representing and exchanging calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information, independent of any particular calendar service or protocol.

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright and License Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format

Desruisseaux Standards Track [Page 1] RFC 5545 iCalendar September 2009

 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
 2.  Basic Grammar and Conventions . . . . . . . . . . . . . . . .   6
   2.1.  Formatting Conventions  . . . . . . . . . . . . . . . . .   6
   2.2.  Related Memos . . . . . . . . . . . . . . . . . . . . . .   7
 3.  iCalendar Object Specification  . . . . . . . . . . . . . . .   8
   3.1.  Content Lines . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.1.  List and Field Separators . . . . . . . . . . . . . .  11
     3.1.2.  Multiple Values . . . . . . . . . . . . . . . . . . .  11
     3.1.3.  Binary Content  . . . . . . . . . . . . . . . . . . .  11
     3.1.4.  Character Set . . . . . . . . . . . . . . . . . . . .  12
   3.2.  Property Parameters . . . . . . . . . . . . . . . . . . .  12
     3.2.1.  Alternate Text Representation . . . . . . . . . . . .  13
     3.2.2.  Common Name . . . . . . . . . . . . . . . . . . . . .  15
     3.2.3.  Calendar User Type  . . . . . . . . . . . . . . . . .  15
     3.2.4.  Delegators  . . . . . . . . . . . . . . . . . . . . .  16
     3.2.5.  Delegatees  . . . . . . . . . . . . . . . . . . . . .  16
     3.2.6.  Directory Entry Reference . . . . . . . . . . . . . .  17
     3.2.7.  Inline Encoding . . . . . . . . . . . . . . . . . . .  17
     3.2.8.  Format Type . . . . . . . . . . . . . . . . . . . . .  18
     3.2.9.  Free/Busy Time Type . . . . . . . . . . . . . . . . .  19
     3.2.10. Language  . . . . . . . . . . . . . . . . . . . . . .  20
     3.2.11. Group or List Membership  . . . . . . . . . . . . . .  20
     3.2.12. Participation Status  . . . . . . . . . . . . . . . .  21
     3.2.13. Recurrence Identifier Range . . . . . . . . . . . . .  22
     3.2.14. Alarm Trigger Relationship  . . . . . . . . . . . . .  23
     3.2.15. Relationship Type . . . . . . . . . . . . . . . . . .  24
     3.2.16. Participation Role  . . . . . . . . . . . . . . . . .  25
     3.2.17. RSVP Expectation  . . . . . . . . . . . . . . . . . .  25
     3.2.18. Sent By . . . . . . . . . . . . . . . . . . . . . . .  26
     3.2.19. Time Zone Identifier  . . . . . . . . . . . . . . . .  26
     3.2.20. Value Data Types  . . . . . . . . . . . . . . . . . .  28
   3.3.  Property Value Data Types . . . . . . . . . . . . . . . .  29
     3.3.1.  Binary  . . . . . . . . . . . . . . . . . . . . . . .  29
     3.3.2.  Boolean . . . . . . . . . . . . . . . . . . . . . . .  30
     3.3.3.  Calendar User Address . . . . . . . . . . . . . . . .  30
     3.3.4.  Date  . . . . . . . . . . . . . . . . . . . . . . . .  31
     3.3.5.  Date-Time . . . . . . . . . . . . . . . . . . . . . .  31
     3.3.6.  Duration  . . . . . . . . . . . . . . . . . . . . . .  34
     3.3.7.  Float . . . . . . . . . . . . . . . . . . . . . . . .  35
     3.3.8.  Integer . . . . . . . . . . . . . . . . . . . . . . .  35
     3.3.9.  Period of Time  . . . . . . . . . . . . . . . . . . .  36
     3.3.10. Recurrence Rule . . . . . . . . . . . . . . . . . . .  37
     3.3.11. Text  . . . . . . . . . . . . . . . . . . . . . . . .  45

Desruisseaux Standards Track [Page 2] RFC 5545 iCalendar September 2009

     3.3.12. Time  . . . . . . . . . . . . . . . . . . . . . . . .  46
     3.3.13. URI . . . . . . . . . . . . . . . . . . . . . . . . .  48
     3.3.14. UTC Offset  . . . . . . . . . . . . . . . . . . . . .  49
   3.4.  iCalendar Object  . . . . . . . . . . . . . . . . . . . .  49
   3.5.  Property  . . . . . . . . . . . . . . . . . . . . . . . .  50
   3.6.  Calendar Components . . . . . . . . . . . . . . . . . . .  50
     3.6.1.  Event Component . . . . . . . . . . . . . . . . . . .  52
     3.6.2.  To-Do Component . . . . . . . . . . . . . . . . . . .  56
     3.6.3.  Journal Component . . . . . . . . . . . . . . . . . .  58
     3.6.4.  Free/Busy Component . . . . . . . . . . . . . . . . .  60
     3.6.5.  Time Zone Component . . . . . . . . . . . . . . . . .  63
     3.6.6.  Alarm Component . . . . . . . . . . . . . . . . . . .  72
   3.7.  Calendar Properties . . . . . . . . . . . . . . . . . . .  77
     3.7.1.  Calendar Scale  . . . . . . . . . . . . . . . . . . .  77
     3.7.2.  Method  . . . . . . . . . . . . . . . . . . . . . . .  78
     3.7.3.  Product Identifier  . . . . . . . . . . . . . . . . .  79
     3.7.4.  Version . . . . . . . . . . . . . . . . . . . . . . .  80
   3.8.  Component Properties  . . . . . . . . . . . . . . . . . .  81
     3.8.1.  Descriptive Component Properties  . . . . . . . . . .  81
       3.8.1.1.  Attachment  . . . . . . . . . . . . . . . . . . .  81
       3.8.1.2.  Categories  . . . . . . . . . . . . . . . . . . .  82
       3.8.1.3.  Classification  . . . . . . . . . . . . . . . . .  83
       3.8.1.4.  Comment . . . . . . . . . . . . . . . . . . . . .  84
       3.8.1.5.  Description . . . . . . . . . . . . . . . . . . .  85
       3.8.1.6.  Geographic Position . . . . . . . . . . . . . . .  87
       3.8.1.7.  Location  . . . . . . . . . . . . . . . . . . . .  88
       3.8.1.8.  Percent Complete  . . . . . . . . . . . . . . . .  89
       3.8.1.9.  Priority  . . . . . . . . . . . . . . . . . . . .  90
       3.8.1.10. Resources . . . . . . . . . . . . . . . . . . . .  92
       3.8.1.11. Status  . . . . . . . . . . . . . . . . . . . . .  93
       3.8.1.12. Summary . . . . . . . . . . . . . . . . . . . . .  94
     3.8.2.  Date and Time Component Properties  . . . . . . . . .  95
       3.8.2.1.  Date-Time Completed . . . . . . . . . . . . . . .  95
       3.8.2.2.  Date-Time End . . . . . . . . . . . . . . . . . .  96
       3.8.2.3.  Date-Time Due . . . . . . . . . . . . . . . . . .  97
       3.8.2.4.  Date-Time Start . . . . . . . . . . . . . . . . .  99
       3.8.2.5.  Duration  . . . . . . . . . . . . . . . . . . . . 100
       3.8.2.6.  Free/Busy Time  . . . . . . . . . . . . . . . . . 101
       3.8.2.7.  Time Transparency . . . . . . . . . . . . . . . . 102
     3.8.3.  Time Zone Component Properties  . . . . . . . . . . . 103
       3.8.3.1.  Time Zone Identifier  . . . . . . . . . . . . . . 103
       3.8.3.2.  Time Zone Name  . . . . . . . . . . . . . . . . . 105
       3.8.3.3.  Time Zone Offset From . . . . . . . . . . . . . . 106
       3.8.3.4.  Time Zone Offset To . . . . . . . . . . . . . . . 106
       3.8.3.5.  Time Zone URL . . . . . . . . . . . . . . . . . . 107
     3.8.4.  Relationship Component Properties . . . . . . . . . . 108
       3.8.4.1.  Attendee  . . . . . . . . . . . . . . . . . . . . 108
       3.8.4.2.  Contact . . . . . . . . . . . . . . . . . . . . . 111

Desruisseaux Standards Track [Page 3] RFC 5545 iCalendar September 2009

       3.8.4.3.  Organizer . . . . . . . . . . . . . . . . . . . . 113
       3.8.4.4.  Recurrence ID . . . . . . . . . . . . . . . . . . 114
       3.8.4.5.  Related To  . . . . . . . . . . . . . . . . . . . 117
       3.8.4.6.  Uniform Resource Locator  . . . . . . . . . . . . 118
       3.8.4.7.  Unique Identifier . . . . . . . . . . . . . . . . 119
     3.8.5.  Recurrence Component Properties . . . . . . . . . . . 120
       3.8.5.1.  Exception Date-Times  . . . . . . . . . . . . . . 120
       3.8.5.2.  Recurrence Date-Times . . . . . . . . . . . . . . 122
       3.8.5.3.  Recurrence Rule . . . . . . . . . . . . . . . . . 124
     3.8.6.  Alarm Component Properties  . . . . . . . . . . . . . 134
       3.8.6.1.  Action  . . . . . . . . . . . . . . . . . . . . . 134
       3.8.6.2.  Repeat Count  . . . . . . . . . . . . . . . . . . 135
       3.8.6.3.  Trigger . . . . . . . . . . . . . . . . . . . . . 135
     3.8.7.  Change Management Component Properties  . . . . . . . 138
       3.8.7.1.  Date-Time Created . . . . . . . . . . . . . . . . 138
       3.8.7.2.  Date-Time Stamp . . . . . . . . . . . . . . . . . 139
       3.8.7.3.  Last Modified . . . . . . . . . . . . . . . . . . 140
       3.8.7.4.  Sequence Number . . . . . . . . . . . . . . . . . 141
     3.8.8.  Miscellaneous Component Properties  . . . . . . . . . 142
       3.8.8.1.  IANA Properties . . . . . . . . . . . . . . . . . 142
       3.8.8.2.  Non-Standard Properties . . . . . . . . . . . . . 142
       3.8.8.3.  Request Status  . . . . . . . . . . . . . . . . . 144
 4.  iCalendar Object Examples . . . . . . . . . . . . . . . . . . 146
 5.  Recommended Practices . . . . . . . . . . . . . . . . . . . . 150
 6.  Internationalization Considerations . . . . . . . . . . . . . 151
 7.  Security Considerations . . . . . . . . . . . . . . . . . . . 151
 8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 151
   8.1.  iCalendar Media Type Registration . . . . . . . . . . . . 151
   8.2.  New iCalendar Elements Registration . . . . . . . . . . . 155
     8.2.1.  iCalendar Elements Registration Procedure . . . . . . 155
     8.2.2.  Registration Template for Components  . . . . . . . . 155
     8.2.3.  Registration Template for Properties  . . . . . . . . 156
     8.2.4.  Registration Template for Parameters  . . . . . . . . 156
     8.2.5.  Registration Template for Value Data Types  . . . . . 157
     8.2.6.  Registration Template for Values  . . . . . . . . . . 157
   8.3.  Initial iCalendar Elements Registries . . . . . . . . . . 158
     8.3.1.  Components Registry . . . . . . . . . . . . . . . . . 158
     8.3.2.  Properties Registry . . . . . . . . . . . . . . . . . 158
     8.3.3.  Parameters Registry . . . . . . . . . . . . . . . . . 161
     8.3.4.  Value Data Types Registry . . . . . . . . . . . . . . 162
     8.3.5.  Calendar User Types Registry  . . . . . . . . . . . . 162
     8.3.6.  Free/Busy Time Types Registry . . . . . . . . . . . . 163
     8.3.7.  Participation Statuses Registry . . . . . . . . . . . 163
     8.3.8.  Relationship Types Registry . . . . . . . . . . . . . 164
     8.3.9.  Participation Roles Registry  . . . . . . . . . . . . 164
     8.3.10. Actions Registry  . . . . . . . . . . . . . . . . . . 165
     8.3.11. Classifications Registry  . . . . . . . . . . . . . . 165
     8.3.12. Methods Registry  . . . . . . . . . . . . . . . . . . 165

Desruisseaux Standards Track [Page 4] RFC 5545 iCalendar September 2009

 9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 165
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . . 166
   10.1. Normative References  . . . . . . . . . . . . . . . . . . 166
   10.2. Informative References  . . . . . . . . . . . . . . . . . 167
 Appendix A.  Differences from RFC 2445  . . . . . . . . . . . . . 169
   A.1.  New Restrictions  . . . . . . . . . . . . . . . . . . . . 169
   A.2.  Restrictions Removed  . . . . . . . . . . . . . . . . . . 169
   A.3.  Deprecated Features . . . . . . . . . . . . . . . . . . . 169

1. Introduction

 The use of calendaring and scheduling has grown considerably in the
 last decade.  Enterprise and inter-enterprise business has become
 dependent on rapid scheduling of events and actions using this
 information technology.  This memo is intended to progress the level
 of interoperability possible between dissimilar calendaring and
 scheduling applications.  This memo defines a MIME content type for
 exchanging electronic calendaring and scheduling information.  The
 Internet Calendaring and Scheduling Core Object Specification, or
 iCalendar, allows for the capture and exchange of information
 normally stored within a calendaring and scheduling application; such
 as a Personal Information Manager (PIM) or a Group-Scheduling
 product.
 The iCalendar format is suitable as an exchange format between
 applications or systems.  The format is defined in terms of a MIME
 content type.  This will enable the object to be exchanged using
 several transports, including but not limited to SMTP, HTTP, a file
 system, desktop interactive protocols such as the use of a memory-
 based clipboard or drag/drop interactions, point-to-point
 asynchronous communication, wired-network transport, or some form of
 unwired transport such as infrared.
 The memo also provides for the definition of iCalendar object methods
 that will map this content type to a set of messages for supporting
 calendaring and scheduling operations such as requesting, replying
 to, modifying, and canceling meetings or appointments, to-dos, and
 journal entries.  The iCalendar object methods can be used to define
 other calendaring and scheduling operations such as requesting for
 and replying with free/busy time data.  Such a scheduling protocol is
 defined in the iCalendar Transport-independent Interoperability
 Protocol (iTIP) defined in [2446bis].
 The memo also includes a formal grammar for the content type based on
 the Internet ABNF defined in [RFC5234].  This ABNF is required for
 the implementation of parsers and to serve as the definitive
 reference when ambiguities or questions arise in interpreting the
 descriptive prose definition of the memo.  Additional restrictions

Desruisseaux Standards Track [Page 5] RFC 5545 iCalendar September 2009

 that could not easily be expressed with the ABNF syntax are specified
 as comments in the ABNF.  Comments with normative statements should
 be treated as such.

2. Basic Grammar and Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].
 This memo makes use of both a descriptive prose and a more formal
 notation for defining the calendaring and scheduling format.
 The notation used in this memo is the ABNF notation of [RFC5234].
 Readers intending on implementing the format defined in this memo
 should be familiar with this notation in order to properly interpret
 the specifications of this memo.
 All numeric values used in this memo are given in decimal notation.
 All names of properties, property parameters, enumerated property
 values, and property parameter values are case-insensitive.  However,
 all other property values are case-sensitive, unless otherwise
 stated.
    Note: All indented editorial notes, such as this one, are intended
    to provide the reader with additional information.  The
    information is not essential to the building of an implementation
    conformant with this memo.  The information is provided to
    highlight a particular feature or characteristic of the memo.
 The format for the iCalendar object is based on the syntax of the
 text/directory media type [RFC2425].  While the iCalendar object is
 not a profile of the text/directory media type [RFC2425], it does
 reuse a number of the elements from the [RFC2425] specification.

2.1. Formatting Conventions

 The elements defined in this memo are defined in prose.  Many of the
 terms used to describe these have common usage that is different than
 the standards usage of this memo.  In order to reference, within this
 memo, elements of the calendaring and scheduling model, core object
 (this memo), or interoperability protocol [2446bis] some formatting
 conventions have been used.  Calendaring and scheduling roles are
 referred to in quoted-strings of text with the first character of
 each word in uppercase.  For example, "Organizer" refers to a role of
 a "Calendar User" within the scheduling protocol defined by
 [2446bis].  Calendar components defined by this memo are referred to

Desruisseaux Standards Track [Page 6] RFC 5545 iCalendar September 2009

 with capitalized, quoted-strings of text.  All calendar components
 start with the letter "V".  For example, "VEVENT" refers to the event
 calendar component, "VTODO" refers to the to-do calendar component,
 and "VJOURNAL" refers to the daily journal calendar component.
 Scheduling methods defined by iTIP [2446bis] are referred to with
 capitalized, quoted-strings of text.  For example, "REQUEST" refers
 to the method for requesting a scheduling calendar component be
 created or modified, and "REPLY" refers to the method a recipient of
 a request uses to update their status with the "Organizer" of the
 calendar component.
 The properties defined by this memo are referred to with capitalized,
 quoted-strings of text, followed by the word "property".  For
 example, "ATTENDEE" property refers to the iCalendar property used to
 convey the calendar address of a calendar user.  Property parameters
 defined by this memo are referred to with lowercase, quoted-strings
 of text, followed by the word "parameter".  For example, "value"
 parameter refers to the iCalendar property parameter used to override
 the default value type for a property value.  Enumerated values
 defined by this memo are referred to with capitalized text, either
 alone or followed by the word "value".  For example, the "MINUTELY"
 value can be used with the "FREQ" component of the "RECUR" value type
 to specify repeating components based on an interval of one minute or
 more.
 The following table lists the different characters from the
 [US-ASCII] character set that is referenced in this document.  For
 each character, the table specifies the character name used
 throughout this document, along with its US-ASCII decimal codepoint.

Desruisseaux Standards Track [Page 7] RFC 5545 iCalendar September 2009

            +------------------------+-------------------+
            | Character name         | Decimal codepoint |
            +------------------------+-------------------+
            | HTAB                   | 9                 |
            | LF                     | 10                |
            | CR                     | 13                |
            | DQUOTE                 | 22                |
            | SPACE                  | 32                |
            | PLUS SIGN              | 43                |
            | COMMA                  | 44                |
            | HYPHEN-MINUS           | 45                |
            | PERIOD                 | 46                |
            | SOLIDUS                | 47                |
            | COLON                  | 58                |
            | SEMICOLON              | 59                |
            | LATIN CAPITAL LETTER N | 78                |
            | LATIN CAPITAL LETTER T | 84                |
            | LATIN CAPITAL LETTER X | 88                |
            | LATIN CAPITAL LETTER Z | 90                |
            | BACKSLASH              | 92                |
            | LATIN SMALL LETTER N   | 110               |
            +------------------------+-------------------+

2.2. Related Memos

 Implementers will need to be familiar with several other memos that,
 along with this memo, form a framework for Internet calendaring and
 scheduling standards.  This memo specifies a core specification of
 objects, value types, properties, and property parameters.
 o  iTIP [2446bis] specifies an interoperability protocol for
    scheduling between different implementations;
 o  iCalendar Message-Based Interoperability Protocol (iMIP) [2447bis]
    specifies an Internet email binding for [2446bis].
 This memo does not attempt to repeat the specification of concepts or
 definitions from these other memos.  Where possible, references are
 made to the memo that provides for the specification of these
 concepts or definitions.

3. iCalendar Object Specification

 The following sections define the details of a Calendaring and
 Scheduling Core Object Specification.  The Calendaring and Scheduling
 Core Object is a collection of calendaring and scheduling
 information.  Typically, this information will consist of an
 iCalendar stream with one or more iCalendar objects.  The body of the

Desruisseaux Standards Track [Page 8] RFC 5545 iCalendar September 2009

 iCalendar object consists of a sequence of calendar properties and
 one or more calendar components.
 Section 3.1 defines the content line format; Section 3.2 defines the
 property parameter format; Section 3.3 defines the data types for
 property values; Section 3.4 defines the iCalendar object format;
 Section 3.5 defines the iCalendar property format; Section 3.6
 defines the calendar component format; Section 3.7 defines calendar
 properties; and Section 3.8 defines calendar component properties.
 This information is intended to be an integral part of the MIME
 content type registration.  In addition, this information can be used
 independent of such content registration.  In particular, this memo
 has direct applicability for use as a calendaring and scheduling
 exchange format in file-, memory-, or network-based transport
 mechanisms.

3.1. Content Lines

 The iCalendar object is organized into individual lines of text,
 called content lines.  Content lines are delimited by a line break,
 which is a CRLF sequence (CR character followed by LF character).
 Lines of text SHOULD NOT be longer than 75 octets, excluding the line
 break.  Long content lines SHOULD be split into a multiple line
 representations using a line "folding" technique.  That is, a long
 line can be split between any two characters by inserting a CRLF
 immediately followed by a single linear white-space character (i.e.,
 SPACE or HTAB).  Any sequence of CRLF followed immediately by a
 single linear white-space character is ignored (i.e., removed) when
 processing the content type.
 For example, the line:
   DESCRIPTION:This is a long description that exists on a long line.
 Can be represented as:
   DESCRIPTION:This is a lo
    ng description
     that exists on a long line.
 The process of moving from this folded multiple-line representation
 to its single-line representation is called "unfolding".  Unfolding
 is accomplished by removing the CRLF and the linear white-space
 character that immediately follows.

Desruisseaux Standards Track [Page 9] RFC 5545 iCalendar September 2009

 When parsing a content line, folded lines MUST first be unfolded
 according to the unfolding procedure described above.
    Note: It is possible for very simple implementations to generate
    improperly folded lines in the middle of a UTF-8 multi-octet
    sequence.  For this reason, implementations need to unfold lines
    in such a way to properly restore the original sequence.
 The content information associated with an iCalendar object is
 formatted using a syntax similar to that defined by [RFC2425].  That
 is, the content information consists of CRLF-separated content lines.
 The following notation defines the lines of content in an iCalendar
 object:
   contentline   = name *(";" param ) ":" value CRLF
   ; This ABNF is just a general definition for an initial parsing
   ; of the content line into its property name, parameter list,
   ; and value string
   ; When parsing a content line, folded lines MUST first
   ; be unfolded according to the unfolding procedure
   ; described above.  When generating a content line, lines
   ; longer than 75 octets SHOULD be folded according to
   ; the folding procedure described above.
   name          = iana-token / x-name
   iana-token    = 1*(ALPHA / DIGIT / "-")
   ; iCalendar identifier registered with IANA
   x-name        = "X-" [vendorid "-"] 1*(ALPHA / DIGIT / "-")
   ; Reserved for experimental use.
   vendorid      = 3*(ALPHA / DIGIT)
   ; Vendor identification
   param         = param-name "=" param-value *("," param-value)
   ; Each property defines the specific ABNF for the parameters
   ; allowed on the property.  Refer to specific properties for
   ; precise parameter ABNF.
   param-name    = iana-token / x-name
   param-value   = paramtext / quoted-string
   paramtext     = *SAFE-CHAR

Desruisseaux Standards Track [Page 10] RFC 5545 iCalendar September 2009

   value         = *VALUE-CHAR
   quoted-string = DQUOTE *QSAFE-CHAR DQUOTE
   QSAFE-CHAR    = WSP / %x21 / %x23-7E / NON-US-ASCII
   ; Any character except CONTROL and DQUOTE
   SAFE-CHAR     = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E
                 / NON-US-ASCII
   ; Any character except CONTROL, DQUOTE, ";", ":", ","
   VALUE-CHAR    = WSP / %x21-7E / NON-US-ASCII
   ; Any textual character
   NON-US-ASCII  = UTF8-2 / UTF8-3 / UTF8-4
   ; UTF8-2, UTF8-3, and UTF8-4 are defined in [RFC3629]
   CONTROL       = %x00-08 / %x0A-1F / %x7F
   ; All the controls except HTAB
 The property value component of a content line has a format that is
 property specific.  Refer to the section describing each property for
 a definition of this format.
 All names of properties, property parameters, enumerated property
 values and property parameter values are case-insensitive.  However,
 all other property values are case-sensitive, unless otherwise
 stated.

3.1.1. List and Field Separators

 Some properties and parameters allow a list of values.  Values in a
 list of values MUST be separated by a COMMA character.  There is no
 significance to the order of values in a list.  For those parameter
 values (such as those that specify URI values) that are specified in
 quoted-strings, the individual quoted-strings are separated by a
 COMMA character.
 Some property values are defined in terms of multiple parts.  These
 structured property values MUST have their value parts separated by a
 SEMICOLON character.
 Some properties allow a list of parameters.  Each property parameter
 in a list of property parameters MUST be separated by a SEMICOLON
 character.

Desruisseaux Standards Track [Page 11] RFC 5545 iCalendar September 2009

 Property parameters with values containing a COLON character, a
 SEMICOLON character or a COMMA character MUST be placed in quoted
 text.
 For example, in the following properties, a SEMICOLON is used to
 separate property parameters from each other and a COMMA character is
 used to separate property values in a value list.
   ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT:mailto:
    jsmith@example.com
   RDATE;VALUE=DATE:19970304,19970504,19970704,19970904

3.1.2. Multiple Values

 Some properties defined in the iCalendar object can have multiple
 values.  The general rule for encoding multi-valued items is to
 simply create a new content line for each value, including the
 property name.  However, it should be noted that some properties
 support encoding multiple values in a single property by separating
 the values with a COMMA character.  Individual property definitions
 should be consulted for determining whether a specific property
 allows multiple values and in which of these two forms.  Multi-valued
 properties MUST NOT be used to specify multiple language variants of
 the same value.  Calendar applications SHOULD display all values.

3.1.3. Binary Content

 Binary content information in an iCalendar object SHOULD be
 referenced using a URI within a property value.  That is, the binary
 content information SHOULD be placed in an external MIME entity that
 can be referenced by a URI from within the iCalendar object.  In
 applications where this is not feasible, binary content information
 can be included within an iCalendar object, but only after first
 encoding it into text using the "BASE64" encoding method defined in
 [RFC4648].  Inline binary content SHOULD only be used in applications
 whose special circumstances demand that an iCalendar object be
 expressed as a single entity.  A property containing inline binary
 content information MUST specify the "ENCODING" property parameter.
 Binary content information placed external to the iCalendar object
 MUST be referenced by a uniform resource identifier (URI).
 The following example specifies an "ATTACH" property that references
 an attachment external to the iCalendar object with a URI reference:
   ATTACH:http://example.com/public/quarterly-report.doc

Desruisseaux Standards Track [Page 12] RFC 5545 iCalendar September 2009

 The following example specifies an "ATTACH" property with inline
 binary encoded content information:
   ATTACH;FMTTYPE=text/plain;ENCODING=BASE64;VALUE=BINARY:VGhlIH
    F1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZy4

3.1.4. Character Set

 There is not a property parameter to declare the charset used in a
 property value.  The default charset for an iCalendar stream is UTF-8
 as defined in [RFC3629].
 The "charset" Content-Type parameter MUST be used in MIME transports
 to specify the charset being used.

3.2. Property Parameters

 A property can have attributes with which it is associated.  These
 "property parameters" contain meta-information about the property or
 the property value.  Property parameters are provided to specify such
 information as the location of an alternate text representation for a
 property value, the language of a text property value, the value type
 of the property value, and other attributes.
 Property parameter values that contain the COLON, SEMICOLON, or COMMA
 character separators MUST be specified as quoted-string text values.
 Property parameter values MUST NOT contain the DQUOTE character.  The
 DQUOTE character is used as a delimiter for parameter values that
 contain restricted characters or URI text.  For example:
   DESCRIPTION;ALTREP="cid:part1.0001@example.org":The Fall'98 Wild
     Wizards Conference - - Las Vegas\, NV\, USA
 Property parameter values that are not in quoted-strings are case-
 insensitive.
 The general property parameters defined by this memo are defined by
 the following notation:

Desruisseaux Standards Track [Page 13] RFC 5545 iCalendar September 2009

   icalparameter = altrepparam       ; Alternate text representation
                 / cnparam           ; Common name
                 / cutypeparam       ; Calendar user type
                 / delfromparam      ; Delegator
                 / deltoparam        ; Delegatee
                 / dirparam          ; Directory entry
                 / encodingparam     ; Inline encoding
                 / fmttypeparam      ; Format type
                 / fbtypeparam       ; Free/busy time type
                 / languageparam     ; Language for text
                 / memberparam       ; Group or list membership
                 / partstatparam     ; Participation status
                 / rangeparam        ; Recurrence identifier range
                 / trigrelparam      ; Alarm trigger relationship
                 / reltypeparam      ; Relationship type
                 / roleparam         ; Participation role
                 / rsvpparam         ; RSVP expectation
                 / sentbyparam       ; Sent by
                 / tzidparam         ; Reference to time zone object
                 / valuetypeparam    ; Property value data type
                 / other-param
   other-param   = (iana-param / x-param)
   iana-param  = iana-token "=" param-value *("," param-value)
   ; Some other IANA-registered iCalendar parameter.
   x-param     = x-name "=" param-value *("," param-value)
   ; A non-standard, experimental parameter.
 Applications MUST ignore x-param and iana-param values they don't
 recognize.

3.2.1. Alternate Text Representation

 Parameter Name:  ALTREP
 Purpose:  To specify an alternate text representation for the
    property value.
 Format Definition:  This property parameter is defined by the
    following notation:
   altrepparam = "ALTREP" "=" DQUOTE uri DQUOTE
 Description:  This parameter specifies a URI that points to an
    alternate representation for a textual property value.  A property
    specifying this parameter MUST also include a value that reflects

Desruisseaux Standards Track [Page 14] RFC 5545 iCalendar September 2009

    the default representation of the text value.  The URI parameter
    value MUST be specified in a quoted-string.
       Note: While there is no restriction imposed on the URI schemes
       allowed for this parameter, Content Identifier (CID) [RFC2392],
       HTTP [RFC2616], and HTTPS [RFC2818] are the URI schemes most
       commonly used by current implementations.
 Example:
     DESCRIPTION;ALTREP="CID:part3.msg.970415T083000@example.com":
      Project XYZ Review Meeting will include the following agenda
       items: (a) Market Overview\, (b) Finances\, (c) Project Man
      agement
    The "ALTREP" property parameter value might point to a "text/html"
    content portion.
     Content-Type:text/html
     Content-Id:<part3.msg.970415T083000@example.com>
     <html>
       <head>
        <title></title>
       </head>
       <body>
         <p>
           <b>Project XYZ Review Meeting</b> will include
           the following agenda items:
           <ol>
             <li>Market Overview</li>
             <li>Finances</li>
             <li>Project Management</li>
           </ol>
         </p>
       </body>
     </html>

3.2.2. Common Name

 Parameter Name:  CN
 Purpose:  To specify the common name to be associated with the
    calendar user specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:

Desruisseaux Standards Track [Page 15] RFC 5545 iCalendar September 2009

   cnparam    = "CN" "=" param-value
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter specifies the common name
    to be associated with the calendar user specified by the property.
    The parameter value is text.  The parameter value can be used for
    display text to be associated with the calendar address specified
    by the property.
 Example:
     ORGANIZER;CN="John Smith":mailto:jsmith@example.com

3.2.3. Calendar User Type

 Parameter Name:  CUTYPE
 Purpose:  To identify the type of calendar user specified by the
    property.
 Format Definition:  This property parameter is defined by the
    following notation:
     cutypeparam        = "CUTYPE" "="
                        ("INDIVIDUAL"   ; An individual
                       / "GROUP"        ; A group of individuals
                       / "RESOURCE"     ; A physical resource
                       / "ROOM"         ; A room resource
                       / "UNKNOWN"      ; Otherwise not known
                       / x-name         ; Experimental type
                       / iana-token)    ; Other IANA-registered
                                        ; type
     ; Default is INDIVIDUAL
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter identifies the type of
    calendar user specified by the property.  If not specified on a
    property that allows this parameter, the default is INDIVIDUAL.
    Applications MUST treat x-name and iana-token values they don't
    recognize the same way as they would the UNKNOWN value.
 Example:
     ATTENDEE;CUTYPE=GROUP:mailto:ietf-calsch@example.org

Desruisseaux Standards Track [Page 16] RFC 5545 iCalendar September 2009

3.2.4. Delegators

 Parameter Name:  DELEGATED-FROM
 Purpose:  To specify the calendar users that have delegated their
    participation to the calendar user specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
     delfromparam       = "DELEGATED-FROM" "=" DQUOTE cal-address
                           DQUOTE *("," DQUOTE cal-address DQUOTE)
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  This parameter specifies those calendar
    users that have delegated their participation in a group-scheduled
    event or to-do to the calendar user specified by the property.
    The individual calendar address parameter values MUST each be
    specified in a quoted-string.
 Example:
     ATTENDEE;DELEGATED-FROM="mailto:jsmith@example.com":mailto:
      jdoe@example.com

3.2.5. Delegatees

 Parameter Name:  DELEGATED-TO
 Purpose:  To specify the calendar users to whom the calendar user
    specified by the property has delegated participation.
 Format Definition:  This property parameter is defined by the
    following notation:
     deltoparam = "DELEGATED-TO" "=" DQUOTE cal-address DQUOTE
                  *("," DQUOTE cal-address DQUOTE)
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  This parameter specifies those calendar
    users whom have been delegated participation in a group-scheduled
    event or to-do by the calendar user specified by the property.
    The individual calendar address parameter values MUST each be
    specified in a quoted-string.

Desruisseaux Standards Track [Page 17] RFC 5545 iCalendar September 2009

 Example:
     ATTENDEE;DELEGATED-TO="mailto:jdoe@example.com","mailto:jqpublic
      @example.com":mailto:jsmith@example.com

3.2.6. Directory Entry Reference

 Parameter Name:  DIR
 Purpose:  To specify reference to a directory entry associated with
    the calendar user specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
     dirparam   = "DIR" "=" DQUOTE uri DQUOTE
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter specifies a reference to
    the directory entry associated with the calendar user specified by
    the property.  The parameter value is a URI.  The URI parameter
    value MUST be specified in a quoted-string.
       Note: While there is no restriction imposed on the URI schemes
       allowed for this parameter, CID [RFC2392], DATA [RFC2397], FILE
       [RFC1738], FTP [RFC1738], HTTP [RFC2616], HTTPS [RFC2818], LDAP
       [RFC4516], and MID [RFC2392] are the URI schemes most commonly
       used by current implementations.
 Example:
     ORGANIZER;DIR="ldap://example.com:6666/o=ABC%20Industries,
      c=US???(cn=Jim%20Dolittle)":mailto:jimdo@example.com

3.2.7. Inline Encoding

 Parameter Name:  ENCODING
 Purpose:  To specify an alternate inline encoding for the property
    value.
 Format Definition:  This property parameter is defined by the
    following notation:

Desruisseaux Standards Track [Page 18] RFC 5545 iCalendar September 2009

     encodingparam      = "ENCODING" "="
                        ( "8BIT"
        ; "8bit" text encoding is defined in [RFC2045]
                        / "BASE64"
        ; "BASE64" binary encoding format is defined in [RFC4648]
                        )
 Description:  This property parameter identifies the inline encoding
    used in a property value.  The default encoding is "8BIT",
    corresponding to a property value consisting of text.  The
    "BASE64" encoding type corresponds to a property value encoded
    using the "BASE64" encoding defined in [RFC2045].
    If the value type parameter is ";VALUE=BINARY", then the inline
    encoding parameter MUST be specified with the value
    ";ENCODING=BASE64".
 Example:
   ATTACH;FMTTYPE=text/plain;ENCODING=BASE64;VALUE=BINARY:TG9yZW
    0gaXBzdW0gZG9sb3Igc2l0IGFtZXQsIGNvbnNlY3RldHVyIGFkaXBpc2ljaW
    5nIGVsaXQsIHNlZCBkbyBlaXVzbW9kIHRlbXBvciBpbmNpZGlkdW50IHV0IG
    xhYm9yZSBldCBkb2xvcmUgbWFnbmEgYWxpcXVhLiBVdCBlbmltIGFkIG1pbm
    ltIHZlbmlhbSwgcXVpcyBub3N0cnVkIGV4ZXJjaXRhdGlvbiB1bGxhbWNvIG
    xhYm9yaXMgbmlzaSB1dCBhbGlxdWlwIGV4IGVhIGNvbW1vZG8gY29uc2VxdW
    F0LiBEdWlzIGF1dGUgaXJ1cmUgZG9sb3IgaW4gcmVwcmVoZW5kZXJpdCBpbi
    B2b2x1cHRhdGUgdmVsaXQgZXNzZSBjaWxsdW0gZG9sb3JlIGV1IGZ1Z2lhdC
    BudWxsYSBwYXJpYXR1ci4gRXhjZXB0ZXVyIHNpbnQgb2NjYWVjYXQgY3VwaW
    RhdGF0IG5vbiBwcm9pZGVudCwgc3VudCBpbiBjdWxwYSBxdWkgb2ZmaWNpYS
    BkZXNlcnVudCBtb2xsaXQgYW5pbSBpZCBlc3QgbGFib3J1bS4=

3.2.8. Format Type

 Parameter Name:  FMTTYPE
 Purpose:  To specify the content type of a referenced object.
 Format Definition:  This property parameter is defined by the
    following notation:
     fmttypeparam = "FMTTYPE" "=" type-name "/" subtype-name
                    ; Where "type-name" and "subtype-name" are
                    ; defined in Section 4.2 of [RFC4288].
 Description:  This parameter can be specified on properties that are
    used to reference an object.  The parameter specifies the media
    type [RFC4288] of the referenced object.  For example, on the
    "ATTACH" property, an FTP type URI value does not, by itself,

Desruisseaux Standards Track [Page 19] RFC 5545 iCalendar September 2009

    necessarily convey the type of content associated with the
    resource.  The parameter value MUST be the text for either an
    IANA-registered media type or a non-standard media type.
 Example:
     ATTACH;FMTTYPE=application/msword:ftp://example.com/pub/docs/
      agenda.doc

3.2.9. Free/Busy Time Type

 Parameter Name:  FBTYPE
 Purpose:  To specify the free or busy time type.
 Format Definition:  This property parameter is defined by the
    following notation:
     fbtypeparam        = "FBTYPE" "=" ("FREE" / "BUSY"
                        / "BUSY-UNAVAILABLE" / "BUSY-TENTATIVE"
                        / x-name
              ; Some experimental iCalendar free/busy type.
                        / iana-token)
              ; Some other IANA-registered iCalendar free/busy type.
 Description:  This parameter specifies the free or busy time type.
    The value FREE indicates that the time interval is free for
    scheduling.  The value BUSY indicates that the time interval is
    busy because one or more events have been scheduled for that
    interval.  The value BUSY-UNAVAILABLE indicates that the time
    interval is busy and that the interval can not be scheduled.  The
    value BUSY-TENTATIVE indicates that the time interval is busy
    because one or more events have been tentatively scheduled for
    that interval.  If not specified on a property that allows this
    parameter, the default is BUSY.  Applications MUST treat x-name
    and iana-token values they don't recognize the same way as they
    would the BUSY value.
 Example:  The following is an example of this parameter on a
    "FREEBUSY" property.
     FREEBUSY;FBTYPE=BUSY:19980415T133000Z/19980415T170000Z

Desruisseaux Standards Track [Page 20] RFC 5545 iCalendar September 2009

3.2.10. Language

 Parameter Name:  LANGUAGE
 Purpose:  To specify the language for text values in a property or
    property parameter.
 Format Definition:  This property parameter is defined by the
    following notation:
     languageparam = "LANGUAGE" "=" language
     language = Language-Tag
                ; As defined in [RFC5646].
 Description:  This parameter identifies the language of the text in
    the property value and of all property parameter values of the
    property.  The value of the "LANGUAGE" property parameter is that
    defined in [RFC5646].
    For transport in a MIME entity, the Content-Language header field
    can be used to set the default language for the entire body part.
    Otherwise, no default language is assumed.
 Example:  The following are examples of this parameter on the
    "SUMMARY" and "LOCATION" properties:
     SUMMARY;LANGUAGE=en-US:Company Holiday Party
     LOCATION;LANGUAGE=en:Germany
     LOCATION;LANGUAGE=no:Tyskland

3.2.11. Group or List Membership

 Parameter Name:  MEMBER
 Purpose:  To specify the group or list membership of the calendar
    user specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
     memberparam        = "MEMBER" "=" DQUOTE cal-address DQUOTE
                          *("," DQUOTE cal-address DQUOTE)

Desruisseaux Standards Track [Page 21] RFC 5545 iCalendar September 2009

 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter identifies the groups or
    list membership for the calendar user specified by the property.
    The parameter value is either a single calendar address in a
    quoted-string or a COMMA-separated list of calendar addresses,
    each in a quoted-string.  The individual calendar address
    parameter values MUST each be specified in a quoted-string.
 Example:
     ATTENDEE;MEMBER="mailto:ietf-calsch@example.org":mailto:
      jsmith@example.com
     ATTENDEE;MEMBER="mailto:projectA@example.com","mailto:pr
      ojectB@example.com":mailto:janedoe@example.com

3.2.12. Participation Status

 Parameter Name:  PARTSTAT
 Purpose:  To specify the participation status for the calendar user
    specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
     partstatparam    = "PARTSTAT" "="
                       (partstat-event
                      / partstat-todo
                      / partstat-jour)
     partstat-event   = ("NEEDS-ACTION"    ; Event needs action
                      / "ACCEPTED"         ; Event accepted
                      / "DECLINED"         ; Event declined
                      / "TENTATIVE"        ; Event tentatively
                                           ; accepted
                      / "DELEGATED"        ; Event delegated
                      / x-name             ; Experimental status
                      / iana-token)        ; Other IANA-registered
                                           ; status
     ; These are the participation statuses for a "VEVENT".
     ; Default is NEEDS-ACTION.
     partstat-todo    = ("NEEDS-ACTION"    ; To-do needs action
                      / "ACCEPTED"         ; To-do accepted
                      / "DECLINED"         ; To-do declined
                      / "TENTATIVE"        ; To-do tentatively
                                           ; accepted

Desruisseaux Standards Track [Page 22] RFC 5545 iCalendar September 2009

                      / "DELEGATED"        ; To-do delegated
                      / "COMPLETED"        ; To-do completed
                                           ; COMPLETED property has
                                           ; DATE-TIME completed
                      / "IN-PROCESS"       ; To-do in process of
                                           ; being completed
                      / x-name             ; Experimental status
                      / iana-token)        ; Other IANA-registered
                                           ; status
     ; These are the participation statuses for a "VTODO".
     ; Default is NEEDS-ACTION.
     partstat-jour    = ("NEEDS-ACTION"    ; Journal needs action
                      / "ACCEPTED"         ; Journal accepted
                      / "DECLINED"         ; Journal declined
                      / x-name             ; Experimental status
                      / iana-token)        ; Other IANA-registered
                                           ; status
     ; These are the participation statuses for a "VJOURNAL".
     ; Default is NEEDS-ACTION.
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter identifies the
    participation status for the calendar user specified by the
    property value.  The parameter values differ depending on whether
    they are associated with a group-scheduled "VEVENT", "VTODO", or
    "VJOURNAL".  The values MUST match one of the values allowed for
    the given calendar component.  If not specified on a property that
    allows this parameter, the default value is NEEDS-ACTION.
    Applications MUST treat x-name and iana-token values they don't
    recognize the same way as they would the NEEDS-ACTION value.
 Example:
     ATTENDEE;PARTSTAT=DECLINED:mailto:jsmith@example.com

3.2.13. Recurrence Identifier Range

 Parameter Name:  RANGE
 Purpose:  To specify the effective range of recurrence instances from
    the instance specified by the recurrence identifier specified by
    the property.
 Format Definition:  This property parameter is defined by the
    following notation:

Desruisseaux Standards Track [Page 23] RFC 5545 iCalendar September 2009

     rangeparam = "RANGE" "=" "THISANDFUTURE"
     ; To specify the instance specified by the recurrence identifier
     ; and all subsequent recurrence instances.
 Description:  This parameter can be specified on a property that
    specifies a recurrence identifier.  The parameter specifies the
    effective range of recurrence instances that is specified by the
    property.  The effective range is from the recurrence identifier
    specified by the property.  If this parameter is not specified on
    an allowed property, then the default range is the single instance
    specified by the recurrence identifier value of the property.  The
    parameter value can only be "THISANDFUTURE" to indicate a range
    defined by the recurrence identifier and all subsequent instances.
    The value "THISANDPRIOR" is deprecated by this revision of
    iCalendar and MUST NOT be generated by applications.
 Example:
     RECURRENCE-ID;RANGE=THISANDFUTURE:19980401T133000Z

3.2.14. Alarm Trigger Relationship

 Parameter Name:  RELATED
 Purpose:  To specify the relationship of the alarm trigger with
    respect to the start or end of the calendar component.
 Format Definition:  This property parameter is defined by the
    following notation:
     trigrelparam       = "RELATED" "="
                         ("START"       ; Trigger off of start
                        / "END")        ; Trigger off of end
 Description:  This parameter can be specified on properties that
    specify an alarm trigger with a "DURATION" value type.  The
    parameter specifies whether the alarm will trigger relative to the
    start or end of the calendar component.  The parameter value START
    will set the alarm to trigger off the start of the calendar
    component; the parameter value END will set the alarm to trigger
    off the end of the calendar component.  If the parameter is not
    specified on an allowable property, then the default is START.
 Example:
     TRIGGER;RELATED=END:PT5M

Desruisseaux Standards Track [Page 24] RFC 5545 iCalendar September 2009

3.2.15. Relationship Type

 Parameter Name:  RELTYPE
 Purpose:  To specify the type of hierarchical relationship associated
    with the calendar component specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
     reltypeparam       = "RELTYPE" "="
                         ("PARENT"    ; Parent relationship - Default
                        / "CHILD"     ; Child relationship
                        / "SIBLING"   ; Sibling relationship
                        / iana-token  ; Some other IANA-registered
                                      ; iCalendar relationship type
                        / x-name)     ; A non-standard, experimental
                                      ; relationship type
 Description:  This parameter can be specified on a property that
    references another related calendar.  The parameter specifies the
    hierarchical relationship type of the calendar component
    referenced by the property.  The parameter value can be PARENT, to
    indicate that the referenced calendar component is a superior of
    calendar component; CHILD to indicate that the referenced calendar
    component is a subordinate of the calendar component; or SIBLING
    to indicate that the referenced calendar component is a peer of
    the calendar component.  If this parameter is not specified on an
    allowable property, the default relationship type is PARENT.
    Applications MUST treat x-name and iana-token values they don't
    recognize the same way as they would the PARENT value.
 Example:
     RELATED-TO;RELTYPE=SIBLING:19960401-080045-4000F192713@
      example.com

3.2.16. Participation Role

 Parameter Name:  ROLE
 Purpose:  To specify the participation role for the calendar user
    specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:

Desruisseaux Standards Track [Page 25] RFC 5545 iCalendar September 2009

     roleparam  = "ROLE" "="
                 ("CHAIR"             ; Indicates chair of the
                                      ; calendar entity
                / "REQ-PARTICIPANT"   ; Indicates a participant whose
                                      ; participation is required
                / "OPT-PARTICIPANT"   ; Indicates a participant whose
                                      ; participation is optional
                / "NON-PARTICIPANT"   ; Indicates a participant who
                                      ; is copied for information
                                      ; purposes only
                / x-name              ; Experimental role
                / iana-token)         ; Other IANA role
     ; Default is REQ-PARTICIPANT
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter specifies the participation
    role for the calendar user specified by the property in the group
    schedule calendar component.  If not specified on a property that
    allows this parameter, the default value is REQ-PARTICIPANT.
    Applications MUST treat x-name and iana-token values they don't
    recognize the same way as they would the REQ-PARTICIPANT value.
 Example:
     ATTENDEE;ROLE=CHAIR:mailto:mrbig@example.com

3.2.17. RSVP Expectation

 Parameter Name:  RSVP
 Purpose:  To specify whether there is an expectation of a favor of a
    reply from the calendar user specified by the property value.
 Format Definition:  This property parameter is defined by the
    following notation:
     rsvpparam = "RSVP" "=" ("TRUE" / "FALSE")
     ; Default is FALSE
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter identifies the expectation
    of a reply from the calendar user specified by the property value.
    This parameter is used by the "Organizer" to request a
    participation status reply from an "Attendee" of a group-scheduled
    event or to-do.  If not specified on a property that allows this
    parameter, the default value is FALSE.

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 Example:
     ATTENDEE;RSVP=TRUE:mailto:jsmith@example.com

3.2.18. Sent By

 Parameter Name:  SENT-BY
 Purpose:  To specify the calendar user that is acting on behalf of
    the calendar user specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
     sentbyparam        = "SENT-BY" "=" DQUOTE cal-address DQUOTE
 Description:  This parameter can be specified on properties with a
    CAL-ADDRESS value type.  The parameter specifies the calendar user
    that is acting on behalf of the calendar user specified by the
    property.  The parameter value MUST be a mailto URI as defined in
    [RFC2368].  The individual calendar address parameter values MUST
    each be specified in a quoted-string.
 Example:
     ORGANIZER;SENT-BY="mailto:sray@example.com":mailto:
      jsmith@example.com

3.2.19. Time Zone Identifier

 Parameter Name:  TZID
 Purpose:  To specify the identifier for the time zone definition for
    a time component in the property value.
 Format Definition:  This property parameter is defined by the
    following notation:
     tzidparam  = "TZID" "=" [tzidprefix] paramtext
     tzidprefix = "/"
 Description:  This parameter MUST be specified on the "DTSTART",
    "DTEND", "DUE", "EXDATE", and "RDATE" properties when either a
    DATE-TIME or TIME value type is specified and when the value is
    neither a UTC or a "floating" time.  Refer to the DATE-TIME or
    TIME value type definition for a description of UTC and "floating
    time" formats.  This property parameter specifies a text value

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    that uniquely identifies the "VTIMEZONE" calendar component to be
    used when evaluating the time portion of the property.  The value
    of the "TZID" property parameter will be equal to the value of the
    "TZID" property for the matching time zone definition.  An
    individual "VTIMEZONE" calendar component MUST be specified for
    each unique "TZID" parameter value specified in the iCalendar
    object.
    The parameter MUST be specified on properties with a DATE-TIME
    value if the DATE-TIME is not either a UTC or a "floating" time.
    Failure to include and follow VTIMEZONE definitions in iCalendar
    objects may lead to inconsistent understanding of the local time
    at any given location.
    The presence of the SOLIDUS character as a prefix, indicates that
    this "TZID" represents a unique ID in a globally defined time zone
    registry (when such registry is defined).
       Note: This document does not define a naming convention for
       time zone identifiers.  Implementers may want to use the naming
       conventions defined in existing time zone specifications such
       as the public-domain TZ database [TZDB].  The specification of
       globally unique time zone identifiers is not addressed by this
       document and is left for future study.
    The following are examples of this property parameter:
     DTSTART;TZID=America/New_York:19980119T020000
     DTEND;TZID=America/New_York:19980119T030000
    The "TZID" property parameter MUST NOT be applied to DATE
    properties and DATE-TIME or TIME properties whose time values are
    specified in UTC.
    The use of local time in a DATE-TIME or TIME value without the
    "TZID" property parameter is to be interpreted as floating time,
    regardless of the existence of "VTIMEZONE" calendar components in
    the iCalendar object.
    For more information, see the sections on the value types DATE-
    TIME and TIME.

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3.2.20. Value Data Types

 Parameter Name:  VALUE
 Purpose:  To explicitly specify the value type format for a property
    value.
 Format Definition:  This property parameter is defined by the
    following notation:
     valuetypeparam = "VALUE" "=" valuetype
     valuetype  = ("BINARY"
                / "BOOLEAN"
                / "CAL-ADDRESS"
                / "DATE"
                / "DATE-TIME"
                / "DURATION"
                / "FLOAT"
                / "INTEGER"
                / "PERIOD"
                / "RECUR"
                / "TEXT"
                / "TIME"
                / "URI"
                / "UTC-OFFSET"
                / x-name
                ; Some experimental iCalendar value type.
                / iana-token)
                ; Some other IANA-registered iCalendar value type.
 Description:  This parameter specifies the value type and format of
    the property value.  The property values MUST be of a single value
    type.  For example, a "RDATE" property cannot have a combination
    of DATE-TIME and TIME value types.
    If the property's value is the default value type, then this
    parameter need not be specified.  However, if the property's
    default value type is overridden by some other allowable value
    type, then this parameter MUST be specified.
    Applications MUST preserve the value data for x-name and iana-
    token values that they don't recognize without attempting to
    interpret or parse the value data.

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3.3. Property Value Data Types

 The properties in an iCalendar object are strongly typed.  The
 definition of each property restricts the value to be one of the
 value data types, or simply value types, defined in this section.
 The value type for a property will either be specified implicitly as
 the default value type or will be explicitly specified with the
 "VALUE" parameter.  If the value type of a property is one of the
 alternate valid types, then it MUST be explicitly specified with the
 "VALUE" parameter.

3.3.1. Binary

 Value Name:  BINARY
 Purpose:  This value type is used to identify properties that contain
    a character encoding of inline binary data.  For example, an
    inline attachment of a document might be included in an iCalendar
    object.
 Format Definition:  This value type is defined by the following
    notation:
     binary     = *(4b-char) [b-end]
     ; A "BASE64" encoded character string, as defined by [RFC4648].
     b-end      = (2b-char "==") / (3b-char "=")
     b-char = ALPHA / DIGIT / "+" / "/"
 Description:  Property values with this value type MUST also include
    the inline encoding parameter sequence of ";ENCODING=BASE64".
    That is, all inline binary data MUST first be character encoded
    using the "BASE64" encoding method defined in [RFC2045].  No
    additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.

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 Example:  The following is an example of a "BASE64" encoded binary
    value data:
   ATTACH;FMTTYPE=image/vnd.microsoft.icon;ENCODING=BASE64;VALUE
    =BINARY:AAABAAEAEBAQAAEABAAoAQAAFgAAACgAAAAQAAAAIAAAAAEABAAA
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAACAAAAAgIAAAICAgADAwMAA////AAAA
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    AAAAAAAAAAAAAAAAAAAAAAMwAAAAAAABNEMQAAAAAAAkQgAAAAAAJEREQgAA
    ACECQ0QgEgAAQxQzM0E0AABERCRCREQAADRDJEJEQwAAAhA0QwEQAAAAAERE
    AAAAAAAAREQAAAAAAAAkQgAAAAAAAAMgAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    AAAAAAAAAAAA

3.3.2. Boolean

 Value Name:  BOOLEAN
 Purpose:  This value type is used to identify properties that contain
    either a "TRUE" or "FALSE" Boolean value.
 Format Definition:  This value type is defined by the following
    notation:
     boolean    = "TRUE" / "FALSE"
 Description:  These values are case-insensitive text.  No additional
    content value encoding (i.e., BACKSLASH character encoding, see
    Section 3.3.11) is defined for this value type.
 Example:  The following is an example of a hypothetical property that
    has a BOOLEAN value type:
     TRUE

3.3.3. Calendar User Address

 Value Name:  CAL-ADDRESS
 Purpose:  This value type is used to identify properties that contain
    a calendar user address.
 Format Definition:  This value type is defined by the following
    notation:
     cal-address        = uri
 Description:  The value is a URI as defined by [RFC3986] or any other
    IANA-registered form for a URI.  When used to address an Internet

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    email transport address for a calendar user, the value MUST be a
    mailto URI, as defined by [RFC2368].  No additional content value
    encoding (i.e., BACKSLASH character encoding, see Section 3.3.11)
    is defined for this value type.
 Example:
  mailto:jane_doe@example.com

3.3.4. Date

 Value Name:  DATE
 Purpose:  This value type is used to identify values that contain a
    calendar date.
 Format Definition:  This value type is defined by the following
    notation:
     date               = date-value
     date-value         = date-fullyear date-month date-mday
     date-fullyear      = 4DIGIT
     date-month         = 2DIGIT        ;01-12
     date-mday          = 2DIGIT        ;01-28, 01-29, 01-30, 01-31
                                        ;based on month/year
 Description:  If the property permits, multiple "date" values are
    specified as a COMMA-separated list of values.  The format for the
    value type is based on the [ISO.8601.2004] complete
    representation, basic format for a calendar date.  The textual
    format specifies a four-digit year, two-digit month, and two-digit
    day of the month.  There are no separator characters between the
    year, month, and day component text.
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.
 Example:  The following represents July 14, 1997:
     19970714

3.3.5. Date-Time

 Value Name:  DATE-TIME
 Purpose:  This value type is used to identify values that specify a
    precise calendar date and time of day.

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 Format Definition:  This value type is defined by the following
    notation:
     date-time  = date "T" time ;As specified in the DATE and TIME
                                ;value definitions
 Description:  If the property permits, multiple "DATE-TIME" values
    are specified as a COMMA-separated list of values.  No additional
    content value encoding (i.e., BACKSLASH character encoding, see
    Section 3.3.11) is defined for this value type.
    The "DATE-TIME" value type is used to identify values that contain
    a precise calendar date and time of day.  The format is based on
    the [ISO.8601.2004] complete representation, basic format for a
    calendar date and time of day.  The text format is a concatenation
    of the "date", followed by the LATIN CAPITAL LETTER T character,
    the time designator, followed by the "time" format.
    The "DATE-TIME" value type expresses time values in three forms:
    The form of date and time with UTC offset MUST NOT be used.  For
    example, the following is not valid for a DATE-TIME value:
     19980119T230000-0800       ;Invalid time format
    FORM #1: DATE WITH LOCAL TIME
    The date with local time form is simply a DATE-TIME value that
    does not contain the UTC designator nor does it reference a time
    zone.  For example, the following represents January 18, 1998, at
    11 PM:
     19980118T230000
    DATE-TIME values of this type are said to be "floating" and are
    not bound to any time zone in particular.  They are used to
    represent the same hour, minute, and second value regardless of
    which time zone is currently being observed.  For example, an
    event can be defined that indicates that an individual will be
    busy from 11:00 AM to 1:00 PM every day, no matter which time zone
    the person is in.  In these cases, a local time can be specified.
    The recipient of an iCalendar object with a property value
    consisting of a local time, without any relative time zone
    information, SHOULD interpret the value as being fixed to whatever
    time zone the "ATTENDEE" is in at any given moment.  This means
    that two "Attendees", in different time zones, receiving the same
    event definition as a floating time, may be participating in the

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    event at different actual times.  Floating time SHOULD only be
    used where that is the reasonable behavior.
    In most cases, a fixed time is desired.  To properly communicate a
    fixed time in a property value, either UTC time or local time with
    time zone reference MUST be specified.
    The use of local time in a DATE-TIME value without the "TZID"
    property parameter is to be interpreted as floating time,
    regardless of the existence of "VTIMEZONE" calendar components in
    the iCalendar object.
    FORM #2: DATE WITH UTC TIME
    The date with UTC time, or absolute time, is identified by a LATIN
    CAPITAL LETTER Z suffix character, the UTC designator, appended to
    the time value.  For example, the following represents January 19,
    1998, at 0700 UTC:
     19980119T070000Z
    The "TZID" property parameter MUST NOT be applied to DATE-TIME
    properties whose time values are specified in UTC.
    FORM #3: DATE WITH LOCAL TIME AND TIME ZONE REFERENCE
    The date and local time with reference to time zone information is
    identified by the use the "TZID" property parameter to reference
    the appropriate time zone definition.  "TZID" is discussed in
    detail in Section 3.2.19.  For example, the following represents
    2:00 A.M. in New York on January 19, 1998:
     TZID=America/New_York:19980119T020000
    If, based on the definition of the referenced time zone, the local
    time described occurs more than once (when changing from daylight
    to standard time), the DATE-TIME value refers to the first
    occurrence of the referenced time.  Thus, TZID=America/
    New_York:20071104T013000 indicates November 4, 2007 at 1:30 A.M.
    EDT (UTC-04:00).  If the local time described does not occur (when
    changing from standard to daylight time), the DATE-TIME value is
    interpreted using the UTC offset before the gap in local times.
    Thus, TZID=America/New_York:20070311T023000 indicates March 11,
    2007 at 3:30 A.M. EDT (UTC-04:00), one hour after 1:30 A.M. EST
    (UTC-05:00).

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    A time value MUST only specify the second 60 when specifying a
    positive leap second.  For example:
     19970630T235960Z
    Implementations that do not support leap seconds SHOULD interpret
    the second 60 as equivalent to the second 59.
 Example:  The following represents July 14, 1997, at 1:30 PM in New
    York City in each of the three time formats, using the "DTSTART"
    property.
     DTSTART:19970714T133000                   ; Local time
     DTSTART:19970714T173000Z                  ; UTC time
     DTSTART;TZID=America/New_York:19970714T133000
                                               ; Local time and time
                                               ; zone reference

3.3.6. Duration

 Value Name:  DURATION
 Purpose:  This value type is used to identify properties that contain
    a duration of time.
 Format Definition:  This value type is defined by the following
    notation:
     dur-value  = (["+"] / "-") "P" (dur-date / dur-time / dur-week)
     dur-date   = dur-day [dur-time]
     dur-time   = "T" (dur-hour / dur-minute / dur-second)
     dur-week   = 1*DIGIT "W"
     dur-hour   = 1*DIGIT "H" [dur-minute]
     dur-minute = 1*DIGIT "M" [dur-second]
     dur-second = 1*DIGIT "S"
     dur-day    = 1*DIGIT "D"
 Description:  If the property permits, multiple "duration" values are
    specified by a COMMA-separated list of values.  The format is
    based on the [ISO.8601.2004] complete representation basic format
    with designators for the duration of time.  The format can
    represent nominal durations (weeks and days) and accurate
    durations (hours, minutes, and seconds).  Note that unlike
    [ISO.8601.2004], this value type doesn't support the "Y" and "M"
    designators to specify durations in terms of years and months.

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    The duration of a week or a day depends on its position in the
    calendar.  In the case of discontinuities in the time scale, such
    as the change from standard time to daylight time and back, the
    computation of the exact duration requires the subtraction or
    addition of the change of duration of the discontinuity.  Leap
    seconds MUST NOT be considered when computing an exact duration.
    When computing an exact duration, the greatest order time
    components MUST be added first, that is, the number of days MUST
    be added first, followed by the number of hours, number of
    minutes, and number of seconds.
    Negative durations are typically used to schedule an alarm to
    trigger before an associated time (see Section 3.8.6.3).
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) are defined for this value type.
 Example:  A duration of 15 days, 5 hours, and 20 seconds would be:
     P15DT5H0M20S
    A duration of 7 weeks would be:
     P7W

3.3.7. Float

 Value Name:  FLOAT
 Purpose:  This value type is used to identify properties that contain
    a real-number value.
 Format Definition:  This value type is defined by the following
    notation:
     float      = (["+"] / "-") 1*DIGIT ["." 1*DIGIT]
 Description:  If the property permits, multiple "float" values are
    specified by a COMMA-separated list of values.
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.
 Example:
     1000000.0000001
     1.333
     -3.14

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3.3.8. Integer

 Value Name:  INTEGER
 Purpose:  This value type is used to identify properties that contain
    a signed integer value.
 Format Definition:  This value type is defined by the following
    notation:
     integer    = (["+"] / "-") 1*DIGIT
 Description:  If the property permits, multiple "integer" values are
    specified by a COMMA-separated list of values.  The valid range
    for "integer" is -2147483648 to 2147483647.  If the sign is not
    specified, then the value is assumed to be positive.
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.
 Example:
     1234567890
     -1234567890
     +1234567890
     432109876

3.3.9. Period of Time

 Value Name:  PERIOD
 Purpose:  This value type is used to identify values that contain a
    precise period of time.
 Format Definition:  This value type is defined by the following
    notation:
     period     = period-explicit / period-start
     period-explicit = date-time "/" date-time
     ; [ISO.8601.2004] complete representation basic format for a
     ; period of time consisting of a start and end.  The start MUST
     ; be before the end.
     period-start = date-time "/" dur-value
     ; [ISO.8601.2004] complete representation basic format for a
     ; period of time consisting of a start and positive duration
     ; of time.

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 Description:  If the property permits, multiple "period" values are
    specified by a COMMA-separated list of values.  There are two
    forms of a period of time.  First, a period of time is identified
    by its start and its end.  This format is based on the
    [ISO.8601.2004] complete representation, basic format for "DATE-
    TIME" start of the period, followed by a SOLIDUS character
    followed by the "DATE-TIME" of the end of the period.  The start
    of the period MUST be before the end of the period.  Second, a
    period of time can also be defined by a start and a positive
    duration of time.  The format is based on the [ISO.8601.2004]
    complete representation, basic format for the "DATE-TIME" start of
    the period, followed by a SOLIDUS character, followed by the
    [ISO.8601.2004] basic format for "DURATION" of the period.
 Example:  The period starting at 18:00:00 UTC, on January 1, 1997 and
    ending at 07:00:00 UTC on January 2, 1997 would be:
     19970101T180000Z/19970102T070000Z
    The period start at 18:00:00 on January 1, 1997 and lasting 5
    hours and 30 minutes would be:
     19970101T180000Z/PT5H30M
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.

3.3.10. Recurrence Rule

 Value Name:  RECUR
 Purpose:  This value type is used to identify properties that contain
    a recurrence rule specification.
 Format Definition:  This value type is defined by the following
    notation:
     recur           = recur-rule-part *( ";" recur-rule-part )
                     ;
                     ; The rule parts are not ordered in any
                     ; particular sequence.
                     ;
                     ; The FREQ rule part is REQUIRED,
                     ; but MUST NOT occur more than once.
                     ;
                     ; The UNTIL or COUNT rule parts are OPTIONAL,
                     ; but they MUST NOT occur in the same 'recur'.
                     ;

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                     ; The other rule parts are OPTIONAL,
                     ; but MUST NOT occur more than once.
     recur-rule-part = ( "FREQ" "=" freq )
                     / ( "UNTIL" "=" enddate )
                     / ( "COUNT" "=" 1*DIGIT )
                     / ( "INTERVAL" "=" 1*DIGIT )
                     / ( "BYSECOND" "=" byseclist )
                     / ( "BYMINUTE" "=" byminlist )
                     / ( "BYHOUR" "=" byhrlist )
                     / ( "BYDAY" "=" bywdaylist )
                     / ( "BYMONTHDAY" "=" bymodaylist )
                     / ( "BYYEARDAY" "=" byyrdaylist )
                     / ( "BYWEEKNO" "=" bywknolist )
                     / ( "BYMONTH" "=" bymolist )
                     / ( "BYSETPOS" "=" bysplist )
                     / ( "WKST" "=" weekday )
     freq        = "SECONDLY" / "MINUTELY" / "HOURLY" / "DAILY"
                 / "WEEKLY" / "MONTHLY" / "YEARLY"
     enddate     = date / date-time
     byseclist   = ( seconds *("," seconds) )
     seconds     = 1*2DIGIT       ;0 to 60
     byminlist   = ( minutes *("," minutes) )
     minutes     = 1*2DIGIT       ;0 to 59
     byhrlist    = ( hour *("," hour) )
     hour        = 1*2DIGIT       ;0 to 23
     bywdaylist  = ( weekdaynum *("," weekdaynum) )
     weekdaynum  = [[plus / minus] ordwk] weekday
     plus        = "+"
     minus       = "-"
     ordwk       = 1*2DIGIT       ;1 to 53
     weekday     = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA"
     ;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
     ;FRIDAY, and SATURDAY days of the week.

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     bymodaylist = ( monthdaynum *("," monthdaynum) )
     monthdaynum = [plus / minus] ordmoday
     ordmoday    = 1*2DIGIT       ;1 to 31
     byyrdaylist = ( yeardaynum *("," yeardaynum) )
     yeardaynum  = [plus / minus] ordyrday
     ordyrday    = 1*3DIGIT      ;1 to 366
     bywknolist  = ( weeknum *("," weeknum) )
     weeknum     = [plus / minus] ordwk
     bymolist    = ( monthnum *("," monthnum) )
     monthnum    = 1*2DIGIT       ;1 to 12
     bysplist    = ( setposday *("," setposday) )
     setposday   = yeardaynum
 Description:  This value type is a structured value consisting of a
    list of one or more recurrence grammar parts.  Each rule part is
    defined by a NAME=VALUE pair.  The rule parts are separated from
    each other by the SEMICOLON character.  The rule parts are not
    ordered in any particular sequence.  Individual rule parts MUST
    only be specified once.  Compliant applications MUST accept rule
    parts ordered in any sequence, but to ensure backward
    compatibility with applications that pre-date this revision of
    iCalendar the FREQ rule part MUST be the first rule part specified
    in a RECUR value.
    The FREQ rule part identifies the type of recurrence rule.  This
    rule part MUST be specified in the recurrence rule.  Valid values
    include SECONDLY, to specify repeating events based on an interval
    of a second or more; MINUTELY, to specify repeating events based
    on an interval of a minute or more; HOURLY, to specify repeating
    events based on an interval of an hour or more; DAILY, to specify
    repeating events based on an interval of a day or more; WEEKLY, to
    specify repeating events based on an interval of a week or more;
    MONTHLY, to specify repeating events based on an interval of a
    month or more; and YEARLY, to specify repeating events based on an
    interval of a year or more.

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    The INTERVAL rule part contains a positive integer representing at
    which intervals the recurrence rule repeats.  The default value is
    "1", meaning every second for a SECONDLY rule, every minute for a
    MINUTELY rule, every hour for an HOURLY rule, every day for a
    DAILY rule, every week for a WEEKLY rule, every month for a
    MONTHLY rule, and every year for a YEARLY rule.  For example,
    within a DAILY rule, a value of "8" means every eight days.
    The UNTIL rule part defines a DATE or DATE-TIME value that bounds
    the recurrence rule in an inclusive manner.  If the value
    specified by UNTIL is synchronized with the specified recurrence,
    this DATE or DATE-TIME becomes the last instance of the
    recurrence.  The value of the UNTIL rule part MUST have the same
    value type as the "DTSTART" property.  Furthermore, if the
    "DTSTART" property is specified as a date with local time, then
    the UNTIL rule part MUST also be specified as a date with local
    time.  If the "DTSTART" property is specified as a date with UTC
    time or a date with local time and time zone reference, then the
    UNTIL rule part MUST be specified as a date with UTC time.  In the
    case of the "STANDARD" and "DAYLIGHT" sub-components the UNTIL
    rule part MUST always be specified as a date with UTC time.  If
    specified as a DATE-TIME value, then it MUST be specified in a UTC
    time format.  If not present, and the COUNT rule part is also not
    present, the "RRULE" is considered to repeat forever.
    The COUNT rule part defines the number of occurrences at which to
    range-bound the recurrence.  The "DTSTART" property value always
    counts as the first occurrence.
    The BYSECOND rule part specifies a COMMA-separated list of seconds
    within a minute.  Valid values are 0 to 60.  The BYMINUTE rule
    part specifies a COMMA-separated list of minutes within an hour.
    Valid values are 0 to 59.  The BYHOUR rule part specifies a COMMA-
    separated list of hours of the day.  Valid values are 0 to 23.
    The BYSECOND, BYMINUTE and BYHOUR rule parts MUST NOT be specified
    when the associated "DTSTART" property has a DATE value type.
    These rule parts MUST be ignored in RECUR value that violate the
    above requirement (e.g., generated by applications that pre-date
    this revision of iCalendar).
    The BYDAY rule part specifies a COMMA-separated list of days of
    the week; SU indicates Sunday; MO indicates Monday; TU indicates
    Tuesday; WE indicates Wednesday; TH indicates Thursday; FR
    indicates Friday; and SA indicates Saturday.
    Each BYDAY value can also be preceded by a positive (+n) or
    negative (-n) integer.  If present, this indicates the nth
    occurrence of a specific day within the MONTHLY or YEARLY "RRULE".

Desruisseaux Standards Track [Page 41] RFC 5545 iCalendar September 2009

    For example, within a MONTHLY rule, +1MO (or simply 1MO)
    represents the first Monday within the month, whereas -1MO
    represents the last Monday of the month.  The numeric value in a
    BYDAY rule part with the FREQ rule part set to YEARLY corresponds
    to an offset within the month when the BYMONTH rule part is
    present, and corresponds to an offset within the year when the
    BYWEEKNO or BYMONTH rule parts are present.  If an integer
    modifier is not present, it means all days of this type within the
    specified frequency.  For example, within a MONTHLY rule, MO
    represents all Mondays within the month.  The BYDAY rule part MUST
    NOT be specified with a numeric value when the FREQ rule part is
    not set to MONTHLY or YEARLY.  Furthermore, the BYDAY rule part
    MUST NOT be specified with a numeric value with the FREQ rule part
    set to YEARLY when the BYWEEKNO rule part is specified.
    The BYMONTHDAY rule part specifies a COMMA-separated list of days
    of the month.  Valid values are 1 to 31 or -31 to -1.  For
    example, -10 represents the tenth to the last day of the month.
    The BYMONTHDAY rule part MUST NOT be specified when the FREQ rule
    part is set to WEEKLY.
    The BYYEARDAY rule part specifies a COMMA-separated list of days
    of the year.  Valid values are 1 to 366 or -366 to -1.  For
    example, -1 represents the last day of the year (December 31st)
    and -306 represents the 306th to the last day of the year (March
    1st).  The BYYEARDAY rule part MUST NOT be specified when the FREQ
    rule part is set to DAILY, WEEKLY, or MONTHLY.
    The BYWEEKNO rule part specifies a COMMA-separated list of
    ordinals specifying weeks of the year.  Valid values are 1 to 53
    or -53 to -1.  This corresponds to weeks according to week
    numbering as defined in [ISO.8601.2004].  A week is defined as a
    seven day period, starting on the day of the week defined to be
    the week start (see WKST).  Week number one of the calendar year
    is the first week that contains at least four (4) days in that
    calendar year.  This rule part MUST NOT be used when the FREQ rule
    part is set to anything other than YEARLY.  For example, 3
    represents the third week of the year.
       Note: Assuming a Monday week start, week 53 can only occur when
       Thursday is January 1 or if it is a leap year and Wednesday is
       January 1.
    The BYMONTH rule part specifies a COMMA-separated list of months
    of the year.  Valid values are 1 to 12.
    The WKST rule part specifies the day on which the workweek starts.
    Valid values are MO, TU, WE, TH, FR, SA, and SU.  This is

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    significant when a WEEKLY "RRULE" has an interval greater than 1,
    and a BYDAY rule part is specified.  This is also significant when
    in a YEARLY "RRULE" when a BYWEEKNO rule part is specified.  The
    default value is MO.
    The BYSETPOS rule part specifies a COMMA-separated list of values
    that corresponds to the nth occurrence within the set of
    recurrence instances specified by the rule.  BYSETPOS operates on
    a set of recurrence instances in one interval of the recurrence
    rule.  For example, in a WEEKLY rule, the interval would be one
    week A set of recurrence instances starts at the beginning of the
    interval defined by the FREQ rule part.  Valid values are 1 to 366
    or -366 to -1.  It MUST only be used in conjunction with another
    BYxxx rule part.  For example "the last work day of the month"
    could be represented as:
     FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-1
    Each BYSETPOS value can include a positive (+n) or negative (-n)
    integer.  If present, this indicates the nth occurrence of the
    specific occurrence within the set of occurrences specified by the
    rule.
    Recurrence rules may generate recurrence instances with an invalid
    date (e.g., February 30) or nonexistent local time (e.g., 1:30 AM
    on a day where the local time is moved forward by an hour at 1:00
    AM).  Such recurrence instances MUST be ignored and MUST NOT be
    counted as part of the recurrence set.
    Information, not contained in the rule, necessary to determine the
    various recurrence instance start time and dates are derived from
    the Start Time ("DTSTART") component attribute.  For example,
    "FREQ=YEARLY;BYMONTH=1" doesn't specify a specific day within the
    month or a time.  This information would be the same as what is
    specified for "DTSTART".
    BYxxx rule parts modify the recurrence in some manner.  BYxxx rule
    parts for a period of time that is the same or greater than the
    frequency generally reduce or limit the number of occurrences of
    the recurrence generated.  For example, "FREQ=DAILY;BYMONTH=1"
    reduces the number of recurrence instances from all days (if
    BYMONTH rule part is not present) to all days in January.  BYxxx
    rule parts for a period of time less than the frequency generally
    increase or expand the number of occurrences of the recurrence.
    For example, "FREQ=YEARLY;BYMONTH=1,2" increases the number of
    days within the yearly recurrence set from 1 (if BYMONTH rule part
    is not present) to 2.

Desruisseaux Standards Track [Page 43] RFC 5545 iCalendar September 2009

    If multiple BYxxx rule parts are specified, then after evaluating
    the specified FREQ and INTERVAL rule parts, the BYxxx rule parts
    are applied to the current set of evaluated occurrences in the
    following order: BYMONTH, BYWEEKNO, BYYEARDAY, BYMONTHDAY, BYDAY,
    BYHOUR, BYMINUTE, BYSECOND and BYSETPOS; then COUNT and UNTIL are
    evaluated.
    The table below summarizes the dependency of BYxxx rule part
    expand or limit behavior on the FREQ rule part value.
    The term "N/A" means that the corresponding BYxxx rule part MUST
    NOT be used with the corresponding FREQ value.
    BYDAY has some special behavior depending on the FREQ value and
    this is described in separate notes below the table.
 +----------+--------+--------+-------+-------+------+-------+------+
 |          |SECONDLY|MINUTELY|HOURLY |DAILY  |WEEKLY|MONTHLY|YEARLY|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYMONTH   |Limit   |Limit   |Limit  |Limit  |Limit |Limit  |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYWEEKNO  |N/A     |N/A     |N/A    |N/A    |N/A   |N/A    |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYYEARDAY |Limit   |Limit   |Limit  |N/A    |N/A   |N/A    |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYMONTHDAY|Limit   |Limit   |Limit  |Limit  |N/A   |Expand |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYDAY     |Limit   |Limit   |Limit  |Limit  |Expand|Note 1 |Note 2|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYHOUR    |Limit   |Limit   |Limit  |Expand |Expand|Expand |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYMINUTE  |Limit   |Limit   |Expand |Expand |Expand|Expand |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYSECOND  |Limit   |Expand  |Expand |Expand |Expand|Expand |Expand|
 +----------+--------+--------+-------+-------+------+-------+------+
 |BYSETPOS  |Limit   |Limit   |Limit  |Limit  |Limit |Limit  |Limit |
 +----------+--------+--------+-------+-------+------+-------+------+
    Note 1:  Limit if BYMONTHDAY is present; otherwise, special expand
             for MONTHLY.
    Note 2:  Limit if BYYEARDAY or BYMONTHDAY is present; otherwise,
             special expand for WEEKLY if BYWEEKNO present; otherwise,
             special expand for MONTHLY if BYMONTH present; otherwise,
             special expand for YEARLY.

Desruisseaux Standards Track [Page 44] RFC 5545 iCalendar September 2009

    Here is an example of evaluating multiple BYxxx rule parts.
     DTSTART;TZID=America/New_York:19970105T083000
     RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;
      BYMINUTE=30
    First, the "INTERVAL=2" would be applied to "FREQ=YEARLY" to
    arrive at "every other year".  Then, "BYMONTH=1" would be applied
    to arrive at "every January, every other year".  Then, "BYDAY=SU"
    would be applied to arrive at "every Sunday in January, every
    other year".  Then, "BYHOUR=8,9" would be applied to arrive at
    "every Sunday in January at 8 AM and 9 AM, every other year".
    Then, "BYMINUTE=30" would be applied to arrive at "every Sunday in
    January at 8:30 AM and 9:30 AM, every other year".  Then, lacking
    information from "RRULE", the second is derived from "DTSTART", to
    end up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM,
    every other year".  Similarly, if the BYMINUTE, BYHOUR, BYDAY,
    BYMONTHDAY, or BYMONTH rule part were missing, the appropriate
    minute, hour, day, or month would have been retrieved from the
    "DTSTART" property.
    If the computed local start time of a recurrence instance does not
    exist, or occurs more than once, for the specified time zone, the
    time of the recurrence instance is interpreted in the same manner
    as an explicit DATE-TIME value describing that date and time, as
    specified in Section 3.3.5.
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.
 Example:  The following is a rule that specifies 10 occurrences that
    occur every other day:
     FREQ=DAILY;COUNT=10;INTERVAL=2
    There are other examples specified in Section 3.8.5.3.

3.3.11. Text

 Value Name:  TEXT
 Purpose:  This value type is used to identify values that contain
    human-readable text.
 Format Definition:  This value type is defined by the following
    notation:

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     text       = *(TSAFE-CHAR / ":" / DQUOTE / ESCAPED-CHAR)
        ; Folded according to description above
     ESCAPED-CHAR = ("\\" / "\;" / "\," / "\N" / "\n")
        ; \\ encodes \, \N or \n encodes newline
        ; \; encodes ;, \, encodes ,
     TSAFE-CHAR = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-5B /
                  %x5D-7E / NON-US-ASCII
        ; Any character except CONTROLs not needed by the current
        ; character set, DQUOTE, ";", ":", "\", ","
 Description:  If the property permits, multiple TEXT values are
    specified by a COMMA-separated list of values.
    The language in which the text is represented can be controlled by
    the "LANGUAGE" property parameter.
    An intentional formatted text line break MUST only be included in
    a "TEXT" property value by representing the line break with the
    character sequence of BACKSLASH, followed by a LATIN SMALL LETTER
    N or a LATIN CAPITAL LETTER N, that is "\n" or "\N".
    The "TEXT" property values may also contain special characters
    that are used to signify delimiters, such as a COMMA character for
    lists of values or a SEMICOLON character for structured values.
    In order to support the inclusion of these special characters in
    "TEXT" property values, they MUST be escaped with a BACKSLASH
    character.  A BACKSLASH character in a "TEXT" property value MUST
    be escaped with another BACKSLASH character.  A COMMA character in
    a "TEXT" property value MUST be escaped with a BACKSLASH
    character.  A SEMICOLON character in a "TEXT" property value MUST
    be escaped with a BACKSLASH character.  However, a COLON character
    in a "TEXT" property value SHALL NOT be escaped with a BACKSLASH
    character.
 Example:  A multiple line value of:
     Project XYZ Final Review
     Conference Room - 3B
     Come Prepared.
    would be represented as:
     Project XYZ Final Review\nConference Room - 3B\nCome Prepared.

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3.3.12. Time

 Value Name:  TIME
 Purpose:  This value type is used to identify values that contain a
    time of day.
 Format Definition:  This value type is defined by the following
    notation:
     time         = time-hour time-minute time-second [time-utc]
     time-hour    = 2DIGIT        ;00-23
     time-minute  = 2DIGIT        ;00-59
     time-second  = 2DIGIT        ;00-60
     ;The "60" value is used to account for positive "leap" seconds.
     time-utc     = "Z"
 Description:  If the property permits, multiple "time" values are
    specified by a COMMA-separated list of values.  No additional
    content value encoding (i.e., BACKSLASH character encoding, see
    Section 3.3.11) is defined for this value type.
    The "TIME" value type is used to identify values that contain a
    time of day.  The format is based on the [ISO.8601.2004] complete
    representation, basic format for a time of day.  The text format
    consists of a two-digit, 24-hour of the day (i.e., values 00-23),
    two-digit minute in the hour (i.e., values 00-59), and two-digit
    seconds in the minute (i.e., values 00-60).  The seconds value of
    60 MUST only be used to account for positive "leap" seconds.
    Fractions of a second are not supported by this format.
    In parallel to the "DATE-TIME" definition above, the "TIME" value
    type expresses time values in three forms:
    The form of time with UTC offset MUST NOT be used.  For example,
    the following is not valid for a time value:
     230000-0800        ;Invalid time format
    FORM #1 LOCAL TIME
    The local time form is simply a time value that does not contain
    the UTC designator nor does it reference a time zone.  For
    example, 11:00 PM:
     230000

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    Time values of this type are said to be "floating" and are not
    bound to any time zone in particular.  They are used to represent
    the same hour, minute, and second value regardless of which time
    zone is currently being observed.  For example, an event can be
    defined that indicates that an individual will be busy from 11:00
    AM to 1:00 PM every day, no matter which time zone the person is
    in.  In these cases, a local time can be specified.  The recipient
    of an iCalendar object with a property value consisting of a local
    time, without any relative time zone information, SHOULD interpret
    the value as being fixed to whatever time zone the "ATTENDEE" is
    in at any given moment.  This means that two "Attendees", may
    participate in the same event at different UTC times; floating
    time SHOULD only be used where that is reasonable behavior.
    In most cases, a fixed time is desired.  To properly communicate a
    fixed time in a property value, either UTC time or local time with
    time zone reference MUST be specified.
    The use of local time in a TIME value without the "TZID" property
    parameter is to be interpreted as floating time, regardless of the
    existence of "VTIMEZONE" calendar components in the iCalendar
    object.
    FORM #2: UTC TIME
    UTC time, or absolute time, is identified by a LATIN CAPITAL
    LETTER Z suffix character, the UTC designator, appended to the
    time value.  For example, the following represents 07:00 AM UTC:
     070000Z
    The "TZID" property parameter MUST NOT be applied to TIME
    properties whose time values are specified in UTC.
    FORM #3: LOCAL TIME AND TIME ZONE REFERENCE
    The local time with reference to time zone information form is
    identified by the use the "TZID" property parameter to reference
    the appropriate time zone definition.  "TZID" is discussed in
    detail in Section 3.2.19.
 Example:  The following represents 8:30 AM in New York in winter,
    five hours behind UTC, in each of the three formats:
     083000
     133000Z
     TZID=America/New_York:083000

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3.3.13. URI

 Value Name:  URI
 Purpose:  This value type is used to identify values that contain a
    uniform resource identifier (URI) type of reference to the
    property value.
 Format Definition:  This value type is defined by the following
    notation:
     uri = <As defined in Section 3 of [RFC3986]>
 Description:  This value type might be used to reference binary
    information, for values that are large, or otherwise undesirable
    to include directly in the iCalendar object.
    Property values with this value type MUST follow the generic URI
    syntax defined in [RFC3986].
    When a property parameter value is a URI value type, the URI MUST
    be specified as a quoted-string value.
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.
 Example:  The following is a URI for a network file:
     http://example.com/my-report.txt

3.3.14. UTC Offset

 Value Name:  UTC-OFFSET
 Purpose:  This value type is used to identify properties that contain
    an offset from UTC to local time.
 Format Definition:  This value type is defined by the following
    notation:
     utc-offset = time-numzone
     time-numzone = ("+" / "-") time-hour time-minute [time-second]
 Description:  The PLUS SIGN character MUST be specified for positive
    UTC offsets (i.e., ahead of UTC).  The HYPHEN-MINUS character MUST
    be specified for negative UTC offsets (i.e., behind of UTC).  The

Desruisseaux Standards Track [Page 49] RFC 5545 iCalendar September 2009

    value of "-0000" and "-000000" are not allowed.  The time-second,
    if present, MUST NOT be 60; if absent, it defaults to zero.
    No additional content value encoding (i.e., BACKSLASH character
    encoding, see Section 3.3.11) is defined for this value type.
 Example:  The following UTC offsets are given for standard time for
    New York (five hours behind UTC) and Geneva (one hour ahead of
    UTC):
  1. 0500
     +0100

3.4. iCalendar Object

 The Calendaring and Scheduling Core Object is a collection of
 calendaring and scheduling information.  Typically, this information
 will consist of an iCalendar stream with a single iCalendar object.
 However, multiple iCalendar objects can be sequentially grouped
 together in an iCalendar stream.  The first line and last line of the
 iCalendar object MUST contain a pair of iCalendar object delimiter
 strings.  The syntax for an iCalendar stream is as follows:
     icalstream = 1*icalobject
     icalobject = "BEGIN" ":" "VCALENDAR" CRLF
                  icalbody
                  "END" ":" "VCALENDAR" CRLF
 The following is a simple example of an iCalendar object:
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//hacksw/handcal//NONSGML v1.0//EN
     BEGIN:VEVENT
     UID:19970610T172345Z-AF23B2@example.com
     DTSTAMP:19970610T172345Z
     DTSTART:19970714T170000Z
     DTEND:19970715T040000Z
     SUMMARY:Bastille Day Party
     END:VEVENT
     END:VCALENDAR

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3.5. Property

 A property is the definition of an individual attribute describing a
 calendar object or a calendar component.  A property takes the form
 defined by the "contentline" notation defined in Section 3.1.
 The following is an example of a property:
     DTSTART:19960415T133000Z
 This memo imposes no ordering of properties within an iCalendar
 object.
 Property names, parameter names, and enumerated parameter values are
 case-insensitive.  For example, the property name "DUE" is the same
 as "due" and "Due", DTSTART;TZID=America/New_York:19980714T120000 is
 the same as DtStart;TzID=America/New_York:19980714T120000.

3.6. Calendar Components

 The body of the iCalendar object consists of a sequence of calendar
 properties and one or more calendar components.  The calendar
 properties are attributes that apply to the calendar object as a
 whole.  The calendar components are collections of properties that
 express a particular calendar semantic.  For example, the calendar
 component can specify an event, a to-do, a journal entry, time zone
 information, free/busy time information, or an alarm.
 The body of the iCalendar object is defined by the following
 notation:
     icalbody   = calprops component
     calprops   = *(
                ;
                ; The following are REQUIRED,
                ; but MUST NOT occur more than once.
                ;
                prodid / version /
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                calscale / method /
                ;
                ; The following are OPTIONAL,
                ; and MAY occur more than once.
                ;

Desruisseaux Standards Track [Page 51] RFC 5545 iCalendar September 2009

                x-prop / iana-prop
                ;
                )
     component  = 1*(eventc / todoc / journalc / freebusyc /
                  timezonec / iana-comp / x-comp)
     iana-comp  = "BEGIN" ":" iana-token CRLF
                  1*contentline
                  "END" ":" iana-token CRLF
     x-comp     = "BEGIN" ":" x-name CRLF
                  1*contentline
                  "END" ":" x-name CRLF
 An iCalendar object MUST include the "PRODID" and "VERSION" calendar
 properties.  In addition, it MUST include at least one calendar
 component.  Special forms of iCalendar objects are possible to
 publish just busy time (i.e., only a "VFREEBUSY" calendar component)
 or time zone (i.e., only a "VTIMEZONE" calendar component)
 information.  In addition, a complex iCalendar object that is used to
 capture a complete snapshot of the contents of a calendar is possible
 (e.g., composite of many different calendar components).  More
 commonly, an iCalendar object will consist of just a single "VEVENT",
 "VTODO", or "VJOURNAL" calendar component.  Applications MUST ignore
 x-comp and iana-comp values they don't recognize.  Applications that
 support importing iCalendar objects SHOULD support all of the
 component types defined in this document, and SHOULD NOT silently
 drop any components as that can lead to user data loss.

3.6.1. Event Component

 Component Name:  VEVENT
 Purpose:  Provide a grouping of component properties that describe an
    event.
 Format Definition:  A "VEVENT" calendar component is defined by the
    following notation:
     eventc     = "BEGIN" ":" "VEVENT" CRLF
                  eventprop *alarmc
                  "END" ":" "VEVENT" CRLF
     eventprop  = *(
                ;
                ; The following are REQUIRED,
                ; but MUST NOT occur more than once.

Desruisseaux Standards Track [Page 52] RFC 5545 iCalendar September 2009

                ;
                dtstamp / uid /
                ;
                ; The following is REQUIRED if the component
                ; appears in an iCalendar object that doesn't
                ; specify the "METHOD" property; otherwise, it
                ; is OPTIONAL; in any case, it MUST NOT occur
                ; more than once.
                ;
                dtstart /
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                class / created / description / geo /
                last-mod / location / organizer / priority /
                seq / status / summary / transp /
                url / recurid /
                ;
                ; The following is OPTIONAL,
                ; but SHOULD NOT occur more than once.
                ;
                rrule /
                ;
                ; Either 'dtend' or 'duration' MAY appear in
                ; a 'eventprop', but 'dtend' and 'duration'
                ; MUST NOT occur in the same 'eventprop'.
                ;
                dtend / duration /
                ;
                ; The following are OPTIONAL,
                ; and MAY occur more than once.
                ;
                attach / attendee / categories / comment /
                contact / exdate / rstatus / related /
                resources / rdate / x-prop / iana-prop
                ;
                )
 Description:  A "VEVENT" calendar component is a grouping of
    component properties, possibly including "VALARM" calendar
    components, that represents a scheduled amount of time on a
    calendar.  For example, it can be an activity; such as a one-hour
    long, department meeting from 8:00 AM to 9:00 AM, tomorrow.
    Generally, an event will take up time on an individual calendar.
    Hence, the event will appear as an opaque interval in a search for
    busy time.  Alternately, the event can have its Time Transparency

Desruisseaux Standards Track [Page 53] RFC 5545 iCalendar September 2009

    set to "TRANSPARENT" in order to prevent blocking of the event in
    searches for busy time.
    The "VEVENT" is also the calendar component used to specify an
    anniversary or daily reminder within a calendar.  These events
    have a DATE value type for the "DTSTART" property instead of the
    default value type of DATE-TIME.  If such a "VEVENT" has a "DTEND"
    property, it MUST be specified as a DATE value also.  The
    anniversary type of "VEVENT" can span more than one date (i.e.,
    "DTEND" property value is set to a calendar date after the
    "DTSTART" property value).  If such a "VEVENT" has a "DURATION"
    property, it MUST be specified as a "dur-day" or "dur-week" value.
    The "DTSTART" property for a "VEVENT" specifies the inclusive
    start of the event.  For recurring events, it also specifies the
    very first instance in the recurrence set.  The "DTEND" property
    for a "VEVENT" calendar component specifies the non-inclusive end
    of the event.  For cases where a "VEVENT" calendar component
    specifies a "DTSTART" property with a DATE value type but no
    "DTEND" nor "DURATION" property, the event's duration is taken to
    be one day.  For cases where a "VEVENT" calendar component
    specifies a "DTSTART" property with a DATE-TIME value type but no
    "DTEND" property, the event ends on the same calendar date and
    time of day specified by the "DTSTART" property.
    The "VEVENT" calendar component cannot be nested within another
    calendar component.  However, "VEVENT" calendar components can be
    related to each other or to a "VTODO" or to a "VJOURNAL" calendar
    component with the "RELATED-TO" property.
 Example:  The following is an example of the "VEVENT" calendar
    component used to represent a meeting that will also be opaque to
    searches for busy time:
     BEGIN:VEVENT
     UID:19970901T130000Z-123401@example.com
     DTSTAMP:19970901T130000Z
     DTSTART:19970903T163000Z
     DTEND:19970903T190000Z
     SUMMARY:Annual Employee Review
     CLASS:PRIVATE
     CATEGORIES:BUSINESS,HUMAN RESOURCES
     END:VEVENT
    The following is an example of the "VEVENT" calendar component
    used to represent a reminder that will not be opaque, but rather
    transparent, to searches for busy time:

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     BEGIN:VEVENT
     UID:19970901T130000Z-123402@example.com
     DTSTAMP:19970901T130000Z
     DTSTART:19970401T163000Z
     DTEND:19970402T010000Z
     SUMMARY:Laurel is in sensitivity awareness class.
     CLASS:PUBLIC
     CATEGORIES:BUSINESS,HUMAN RESOURCES
     TRANSP:TRANSPARENT
     END:VEVENT
    The following is an example of the "VEVENT" calendar component
    used to represent an anniversary that will occur annually:
     BEGIN:VEVENT
     UID:19970901T130000Z-123403@example.com
     DTSTAMP:19970901T130000Z
     DTSTART;VALUE=DATE:19971102
     SUMMARY:Our Blissful Anniversary
     TRANSP:TRANSPARENT
     CLASS:CONFIDENTIAL
     CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION
     RRULE:FREQ=YEARLY
     END:VEVENT
    The following is an example of the "VEVENT" calendar component
    used to represent a multi-day event scheduled from June 28th, 2007
    to July 8th, 2007 inclusively.  Note that the "DTEND" property is
    set to July 9th, 2007, since the "DTEND" property specifies the
    non-inclusive end of the event.
     BEGIN:VEVENT
     UID:20070423T123432Z-541111@example.com
     DTSTAMP:20070423T123432Z
     DTSTART;VALUE=DATE:20070628
     DTEND;VALUE=DATE:20070709
     SUMMARY:Festival International de Jazz de Montreal
     TRANSP:TRANSPARENT
     END:VEVENT

3.6.2. To-Do Component

 Component Name:  VTODO
 Purpose:  Provide a grouping of calendar properties that describe a
    to-do.

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 Format Definition:  A "VTODO" calendar component is defined by the
    following notation:
     todoc      = "BEGIN" ":" "VTODO" CRLF
                  todoprop *alarmc
                  "END" ":" "VTODO" CRLF
     todoprop   = *(
                ;
                ; The following are REQUIRED,
                ; but MUST NOT occur more than once.
                ;
                dtstamp / uid /
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                class / completed / created / description /
                dtstart / geo / last-mod / location / organizer /
                percent / priority / recurid / seq / status /
                summary / url /
                ;
                ; The following is OPTIONAL,
                ; but SHOULD NOT occur more than once.
                ;
                rrule /
                ;
                ; Either 'due' or 'duration' MAY appear in
                ; a 'todoprop', but 'due' and 'duration'
                ; MUST NOT occur in the same 'todoprop'.
                ; If 'duration' appear in a 'todoprop',
                ; then 'dtstart' MUST also appear in
                ; the same 'todoprop'.
                ;
                due / duration /
                ;
                ; The following are OPTIONAL,
                ; and MAY occur more than once.
                ;
                attach / attendee / categories / comment / contact /
                exdate / rstatus / related / resources /
                rdate / x-prop / iana-prop
                ;
                )
 Description:  A "VTODO" calendar component is a grouping of component
    properties and possibly "VALARM" calendar components that
    represent an action-item or assignment.  For example, it can be

Desruisseaux Standards Track [Page 56] RFC 5545 iCalendar September 2009

    used to represent an item of work assigned to an individual; such
    as "turn in travel expense today".
    The "VTODO" calendar component cannot be nested within another
    calendar component.  However, "VTODO" calendar components can be
    related to each other or to a "VEVENT" or to a "VJOURNAL" calendar
    component with the "RELATED-TO" property.
    A "VTODO" calendar component without the "DTSTART" and "DUE" (or
    "DURATION") properties specifies a to-do that will be associated
    with each successive calendar date, until it is completed.
 Examples:  The following is an example of a "VTODO" calendar
    component that needs to be completed before May 1st, 2007.  On
    midnight May 1st, 2007 this to-do would be considered overdue.
     BEGIN:VTODO
     UID:20070313T123432Z-456553@example.com
     DTSTAMP:20070313T123432Z
     DUE;VALUE=DATE:20070501
     SUMMARY:Submit Quebec Income Tax Return for 2006
     CLASS:CONFIDENTIAL
     CATEGORIES:FAMILY,FINANCE
     STATUS:NEEDS-ACTION
     END:VTODO
    The following is an example of a "VTODO" calendar component that
    was due before 1:00 P.M. UTC on July 9th, 2007 and was completed
    on July 7th, 2007 at 10:00 A.M. UTC.
     BEGIN:VTODO
     UID:20070514T103211Z-123404@example.com
     DTSTAMP:20070514T103211Z
     DTSTART:20070514T110000Z
     DUE:20070709T130000Z
     COMPLETED:20070707T100000Z
     SUMMARY:Submit Revised Internet-Draft
     PRIORITY:1
     STATUS:NEEDS-ACTION
     END:VTODO

3.6.3. Journal Component

 Component Name:  VJOURNAL
 Purpose:  Provide a grouping of component properties that describe a
    journal entry.

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 Format Definition:  A "VJOURNAL" calendar component is defined by the
    following notation:
     journalc   = "BEGIN" ":" "VJOURNAL" CRLF
                  jourprop
                  "END" ":" "VJOURNAL" CRLF
     jourprop   = *(
                ;
                ; The following are REQUIRED,
                ; but MUST NOT occur more than once.
                ;
                dtstamp / uid /
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                class / created / dtstart /
                last-mod / organizer / recurid / seq /
                status / summary / url /
                ;
                ; The following is OPTIONAL,
                ; but SHOULD NOT occur more than once.
                ;
                rrule /
                ;
                ; The following are OPTIONAL,
                ; and MAY occur more than once.
                ;
                attach / attendee / categories / comment /
                contact / description / exdate / related / rdate /
                rstatus / x-prop / iana-prop
                ;
                )
 Description:  A "VJOURNAL" calendar component is a grouping of
    component properties that represent one or more descriptive text
    notes associated with a particular calendar date.  The "DTSTART"
    property is used to specify the calendar date with which the
    journal entry is associated.  Generally, it will have a DATE value
    data type, but it can also be used to specify a DATE-TIME value
    data type.  Examples of a journal entry include a daily record of
    a legislative body or a journal entry of individual telephone
    contacts for the day or an ordered list of accomplishments for the
    day.  The "VJOURNAL" calendar component can also be used to
    associate a document with a calendar date.

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    The "VJOURNAL" calendar component does not take up time on a
    calendar.  Hence, it does not play a role in free or busy time
    searches -- it is as though it has a time transparency value of
    TRANSPARENT.  It is transparent to any such searches.
    The "VJOURNAL" calendar component cannot be nested within another
    calendar component.  However, "VJOURNAL" calendar components can
    be related to each other or to a "VEVENT" or to a "VTODO" calendar
    component, with the "RELATED-TO" property.
 Example:  The following is an example of the "VJOURNAL" calendar
    component:
     BEGIN:VJOURNAL
     UID:19970901T130000Z-123405@example.com
     DTSTAMP:19970901T130000Z
     DTSTART;VALUE=DATE:19970317
     SUMMARY:Staff meeting minutes
     DESCRIPTION:1. Staff meeting: Participants include Joe\,
       Lisa\, and Bob. Aurora project plans were reviewed.
       There is currently no budget reserves for this project.
       Lisa will escalate to management. Next meeting on Tuesday.\n
      2. Telephone Conference: ABC Corp. sales representative
       called to discuss new printer. Promised to get us a demo by
       Friday.\n3. Henry Miller (Handsoff Insurance): Car was
       totaled by tree. Is looking into a loaner car. 555-2323
       (tel).
     END:VJOURNAL

3.6.4. Free/Busy Component

 Component Name:  VFREEBUSY
 Purpose:  Provide a grouping of component properties that describe
    either a request for free/busy time, describe a response to a
    request for free/busy time, or describe a published set of busy
    time.
 Format Definition:  A "VFREEBUSY" calendar component is defined by
    the following notation:
     freebusyc  = "BEGIN" ":" "VFREEBUSY" CRLF
                  fbprop
                  "END" ":" "VFREEBUSY" CRLF
     fbprop     = *(
                ;
                ; The following are REQUIRED,

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                ; but MUST NOT occur more than once.
                ;
                dtstamp / uid /
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                contact / dtstart / dtend /
                organizer / url /
                ;
                ; The following are OPTIONAL,
                ; and MAY occur more than once.
                ;
                attendee / comment / freebusy / rstatus / x-prop /
                iana-prop
                ;
                )
 Description:  A "VFREEBUSY" calendar component is a grouping of
    component properties that represents either a request for free or
    busy time information, a reply to a request for free or busy time
    information, or a published set of busy time information.
    When used to request free/busy time information, the "ATTENDEE"
    property specifies the calendar users whose free/busy time is
    being requested; the "ORGANIZER" property specifies the calendar
    user who is requesting the free/busy time; the "DTSTART" and
    "DTEND" properties specify the window of time for which the free/
    busy time is being requested; the "UID" and "DTSTAMP" properties
    are specified to assist in proper sequencing of multiple free/busy
    time requests.
    When used to reply to a request for free/busy time, the "ATTENDEE"
    property specifies the calendar user responding to the free/busy
    time request; the "ORGANIZER" property specifies the calendar user
    that originally requested the free/busy time; the "FREEBUSY"
    property specifies the free/busy time information (if it exists);
    and the "UID" and "DTSTAMP" properties are specified to assist in
    proper sequencing of multiple free/busy time replies.
    When used to publish busy time, the "ORGANIZER" property specifies
    the calendar user associated with the published busy time; the
    "DTSTART" and "DTEND" properties specify an inclusive time window
    that surrounds the busy time information; the "FREEBUSY" property
    specifies the published busy time information; and the "DTSTAMP"
    property specifies the DATE-TIME that iCalendar object was
    created.

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    The "VFREEBUSY" calendar component cannot be nested within another
    calendar component.  Multiple "VFREEBUSY" calendar components can
    be specified within an iCalendar object.  This permits the
    grouping of free/busy information into logical collections, such
    as monthly groups of busy time information.
    The "VFREEBUSY" calendar component is intended for use in
    iCalendar object methods involving requests for free time,
    requests for busy time, requests for both free and busy, and the
    associated replies.
    Free/Busy information is represented with the "FREEBUSY" property.
    This property provides a terse representation of time periods.
    One or more "FREEBUSY" properties can be specified in the
    "VFREEBUSY" calendar component.
    When present in a "VFREEBUSY" calendar component, the "DTSTART"
    and "DTEND" properties SHOULD be specified prior to any "FREEBUSY"
    properties.
    The recurrence properties ("RRULE", "RDATE", "EXDATE") are not
    permitted within a "VFREEBUSY" calendar component.  Any recurring
    events are resolved into their individual busy time periods using
    the "FREEBUSY" property.
 Example:  The following is an example of a "VFREEBUSY" calendar
    component used to request free or busy time information:
     BEGIN:VFREEBUSY
     UID:19970901T082949Z-FA43EF@example.com
     ORGANIZER:mailto:jane_doe@example.com
     ATTENDEE:mailto:john_public@example.com
     DTSTART:19971015T050000Z
     DTEND:19971016T050000Z
     DTSTAMP:19970901T083000Z
     END:VFREEBUSY

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    The following is an example of a "VFREEBUSY" calendar component
    used to reply to the request with busy time information:
     BEGIN:VFREEBUSY
     UID:19970901T095957Z-76A912@example.com
     ORGANIZER:mailto:jane_doe@example.com
     ATTENDEE:mailto:john_public@example.com
     DTSTAMP:19970901T100000Z
     FREEBUSY:19971015T050000Z/PT8H30M,
      19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M
     URL:http://example.com/pub/busy/jpublic-01.ifb
     COMMENT:This iCalendar file contains busy time information for
       the next three months.
     END:VFREEBUSY
    The following is an example of a "VFREEBUSY" calendar component
    used to publish busy time information:
     BEGIN:VFREEBUSY
     UID:19970901T115957Z-76A912@example.com
     DTSTAMP:19970901T120000Z
     ORGANIZER:jsmith@example.com
     DTSTART:19980313T141711Z
     DTEND:19980410T141711Z
     FREEBUSY:19980314T233000Z/19980315T003000Z
     FREEBUSY:19980316T153000Z/19980316T163000Z
     FREEBUSY:19980318T030000Z/19980318T040000Z
     URL:http://www.example.com/calendar/busytime/jsmith.ifb
     END:VFREEBUSY

3.6.5. Time Zone Component

 Component Name:  VTIMEZONE
 Purpose:  Provide a grouping of component properties that defines a
    time zone.
 Format Definition:  A "VTIMEZONE" calendar component is defined by
    the following notation:
     timezonec  = "BEGIN" ":" "VTIMEZONE" CRLF
                  *(
                  ;
                  ; 'tzid' is REQUIRED, but MUST NOT occur more
                  ; than once.
                  ;
                  tzid /
                  ;

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                  ; 'last-mod' and 'tzurl' are OPTIONAL,
                  ; but MUST NOT occur more than once.
                  ;
                  last-mod / tzurl /
                  ;
                  ; One of 'standardc' or 'daylightc' MUST occur
                  ; and each MAY occur more than once.
                  ;
                  standardc / daylightc /
                  ;
                  ; The following are OPTIONAL,
                  ; and MAY occur more than once.
                  ;
                  x-prop / iana-prop
                  ;
                  )
                  "END" ":" "VTIMEZONE" CRLF
     standardc  = "BEGIN" ":" "STANDARD" CRLF
                  tzprop
                  "END" ":" "STANDARD" CRLF
     daylightc  = "BEGIN" ":" "DAYLIGHT" CRLF
                  tzprop
                  "END" ":" "DAYLIGHT" CRLF
     tzprop     = *(
                  ;
                  ; The following are REQUIRED,
                  ; but MUST NOT occur more than once.
                  ;
                  dtstart / tzoffsetto / tzoffsetfrom /
                  ;
                  ; The following is OPTIONAL,
                  ; but SHOULD NOT occur more than once.
                  ;
                  rrule /
                  ;
                  ; The following are OPTIONAL,
                  ; and MAY occur more than once.
                  ;
                  comment / rdate / tzname / x-prop / iana-prop
                  ;
                  )
 Description:  A time zone is unambiguously defined by the set of time
    measurement rules determined by the governing body for a given
    geographic area.  These rules describe, at a minimum, the base

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    offset from UTC for the time zone, often referred to as the
    Standard Time offset.  Many locations adjust their Standard Time
    forward or backward by one hour, in order to accommodate seasonal
    changes in number of daylight hours, often referred to as Daylight
    Saving Time.  Some locations adjust their time by a fraction of an
    hour.  Standard Time is also known as Winter Time.  Daylight
    Saving Time is also known as Advanced Time, Summer Time, or Legal
    Time in certain countries.  The following table shows the changes
    in time zone rules in effect for New York City starting from 1967.
    Each line represents a description or rule for a particular
    observance.
                       Effective Observance Rule
   +-----------+--------------------------+--------+--------------+
   | Date      | (Date-Time)              | Offset | Abbreviation |
   +-----------+--------------------------+--------+--------------+
   | 1967-1973 | last Sun in Apr, 02:00   | -0400  | EDT          |
   |           |                          |        |              |
   | 1967-2006 | last Sun in Oct, 02:00   | -0500  | EST          |
   |           |                          |        |              |
   | 1974-1974 | Jan 6, 02:00             | -0400  | EDT          |
   |           |                          |        |              |
   | 1975-1975 | Feb 23, 02:00            | -0400  | EDT          |
   |           |                          |        |              |
   | 1976-1986 | last Sun in Apr, 02:00   | -0400  | EDT          |
   |           |                          |        |              |
   | 1987-2006 | first Sun in Apr, 02:00  | -0400  | EDT          |
   |           |                          |        |              |
   | 2007-*    | second Sun in Mar, 02:00 | -0400  | EDT          |
   |           |                          |        |              |
   | 2007-*    | first Sun in Nov, 02:00  | -0500  | EST          |
   +-----------+--------------------------+--------+--------------+
 Note: The specification of a global time zone registry is not
       addressed by this document and is left for future study.
       However, implementers may find the TZ database [TZDB] a useful
       reference.  It is an informal, public-domain collection of time
       zone information, which is currently being maintained by
       volunteer Internet participants, and is used in several
       operating systems.  This database contains current and
       historical time zone information for a wide variety of
       locations around the globe; it provides a time zone identifier
       for every unique time zone rule set in actual use since 1970,
       with historical data going back to the introduction of standard
       time.

Desruisseaux Standards Track [Page 64] RFC 5545 iCalendar September 2009

    Interoperability between two calendaring and scheduling
    applications, especially for recurring events, to-dos or journal
    entries, is dependent on the ability to capture and convey date
    and time information in an unambiguous format.  The specification
    of current time zone information is integral to this behavior.
    If present, the "VTIMEZONE" calendar component defines the set of
    Standard Time and Daylight Saving Time observances (or rules) for
    a particular time zone for a given interval of time.  The
    "VTIMEZONE" calendar component cannot be nested within other
    calendar components.  Multiple "VTIMEZONE" calendar components can
    exist in an iCalendar object.  In this situation, each "VTIMEZONE"
    MUST represent a unique time zone definition.  This is necessary
    for some classes of events, such as airline flights, that start in
    one time zone and end in another.
    The "VTIMEZONE" calendar component MUST include the "TZID"
    property and at least one definition of a "STANDARD" or "DAYLIGHT"
    sub-component.  The "STANDARD" or "DAYLIGHT" sub-component MUST
    include the "DTSTART", "TZOFFSETFROM", and "TZOFFSETTO"
    properties.
    An individual "VTIMEZONE" calendar component MUST be specified for
    each unique "TZID" parameter value specified in the iCalendar
    object.  In addition, a "VTIMEZONE" calendar component, referred
    to by a recurring calendar component, MUST provide valid time zone
    information for all recurrence instances.
    Each "VTIMEZONE" calendar component consists of a collection of
    one or more sub-components that describe the rule for a particular
    observance (either a Standard Time or a Daylight Saving Time
    observance).  The "STANDARD" sub-component consists of a
    collection of properties that describe Standard Time.  The
    "DAYLIGHT" sub-component consists of a collection of properties
    that describe Daylight Saving Time.  In general, this collection
    of properties consists of:
  • the first onset DATE-TIME for the observance;
  • the last onset DATE-TIME for the observance, if a last onset is

known;

  • the offset to be applied for the observance;
  • a rule that describes the day and time when the observance

takes effect;

  • an optional name for the observance.

Desruisseaux Standards Track [Page 65] RFC 5545 iCalendar September 2009

    For a given time zone, there may be multiple unique definitions of
    the observances over a period of time.  Each observance is
    described using either a "STANDARD" or "DAYLIGHT" sub-component.
    The collection of these sub-components is used to describe the
    time zone for a given period of time.  The offset to apply at any
    given time is found by locating the observance that has the last
    onset date and time before the time in question, and using the
    offset value from that observance.
    The top-level properties in a "VTIMEZONE" calendar component are:
    The mandatory "TZID" property is a text value that uniquely
    identifies the "VTIMEZONE" calendar component within the scope of
    an iCalendar object.
    The optional "LAST-MODIFIED" property is a UTC value that
    specifies the date and time that this time zone definition was
    last updated.
    The optional "TZURL" property is a url value that points to a
    published "VTIMEZONE" definition.  "TZURL" SHOULD refer to a
    resource that is accessible by anyone who might need to interpret
    the object.  This SHOULD NOT normally be a "file" URL or other URL
    that is not widely accessible.
    The collection of properties that are used to define the
    "STANDARD" and "DAYLIGHT" sub-components include:
    The mandatory "DTSTART" property gives the effective onset date
    and local time for the time zone sub-component definition.
    "DTSTART" in this usage MUST be specified as a date with a local
    time value.
    The mandatory "TZOFFSETFROM" property gives the UTC offset that is
    in use when the onset of this time zone observance begins.
    "TZOFFSETFROM" is combined with "DTSTART" to define the effective
    onset for the time zone sub-component definition.  For example,
    the following represents the time at which the observance of
    Standard Time took effect in Fall 1967 for New York City:
     DTSTART:19671029T020000
     TZOFFSETFROM:-0400
    The mandatory "TZOFFSETTO" property gives the UTC offset for the
    time zone sub-component (Standard Time or Daylight Saving Time)
    when this observance is in use.

Desruisseaux Standards Track [Page 66] RFC 5545 iCalendar September 2009

    The optional "TZNAME" property is the customary name for the time
    zone.  This could be used for displaying dates.
    The onset DATE-TIME values for the observance defined by the time
    zone sub-component is defined by the "DTSTART", "RRULE", and
    "RDATE" properties.
    The "RRULE" property defines the recurrence rule for the onset of
    the observance defined by this time zone sub-component.  Some
    specific requirements for the usage of "RRULE" for this purpose
    include:
  • If observance is known to have an effective end date, the

"UNTIL" recurrence rule parameter MUST be used to specify the

       last valid onset of this observance (i.e., the UNTIL DATE-TIME
       will be equal to the last instance generated by the recurrence
       pattern).  It MUST be specified in UTC time.
  • The "DTSTART" and the "TZOFFSETFROM" properties MUST be used

when generating the onset DATE-TIME values (instances) from the

       "RRULE".
    The "RDATE" property can also be used to define the onset of the
    observance by giving the individual onset date and times.  "RDATE"
    in this usage MUST be specified as a date with local time value,
    relative to the UTC offset specified in the "TZOFFSETFROM"
    property.
    The optional "COMMENT" property is also allowed for descriptive
    explanatory text.
 Example:  The following are examples of the "VTIMEZONE" calendar
    component:
    This is an example showing all the time zone rules for New York
    City since April 30, 1967 at 03:00:00 EDT.
     BEGIN:VTIMEZONE
     TZID:America/New_York
     LAST-MODIFIED:20050809T050000Z
     BEGIN:DAYLIGHT
     DTSTART:19670430T020000
     RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=-1SU;UNTIL=19730429T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:STANDARD

Desruisseaux Standards Track [Page 67] RFC 5545 iCalendar September 2009

     DTSTART:19671029T020000
     RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU;UNTIL=20061029T060000Z
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19740106T020000
     RDATE:19750223T020000
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:DAYLIGHT
     DTSTART:19760425T020000
     RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=-1SU;UNTIL=19860427T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:DAYLIGHT
     DTSTART:19870405T020000
     RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=1SU;UNTIL=20060402T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:DAYLIGHT
     DTSTART:20070311T020000
     RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:STANDARD
     DTSTART:20071104T020000
     RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     END:VTIMEZONE
    This is an example showing time zone information for New York City
    using only the "DTSTART" property.  Note that this is only
    suitable for a recurring event that starts on or later than March
    11, 2007 at 03:00:00 EDT (i.e., the earliest effective transition
    date and time) and ends no later than March 9, 2008 at 01:59:59

Desruisseaux Standards Track [Page 68] RFC 5545 iCalendar September 2009

    EST (i.e., latest valid date and time for EST in this scenario).
    For example, this can be used for a recurring event that occurs
    every Friday, 8:00 A.M.-9:00 A.M., starting June 1, 2007, ending
    December 31, 2007,
     BEGIN:VTIMEZONE
     TZID:America/New_York
     LAST-MODIFIED:20050809T050000Z
     BEGIN:STANDARD
     DTSTART:20071104T020000
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:20070311T020000
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE
    This is a simple example showing the current time zone rules for
    New York City using a "RRULE" recurrence pattern.  Note that there
    is no effective end date to either of the Standard Time or
    Daylight Time rules.  This information would be valid for a
    recurring event starting today and continuing indefinitely.
     BEGIN:VTIMEZONE
     TZID:America/New_York
     LAST-MODIFIED:20050809T050000Z
     TZURL:http://zones.example.com/tz/America-New_York.ics
     BEGIN:STANDARD
     DTSTART:20071104T020000
     RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:20070311T020000
     RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

Desruisseaux Standards Track [Page 69] RFC 5545 iCalendar September 2009

    This is an example showing a set of rules for a fictitious time
    zone where the Daylight Time rule has an effective end date (i.e.,
    after that date, Daylight Time is no longer observed).
     BEGIN:VTIMEZONE
     TZID:Fictitious
     LAST-MODIFIED:19870101T000000Z
     BEGIN:STANDARD
     DTSTART:19671029T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19870405T020000
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

Desruisseaux Standards Track [Page 70] RFC 5545 iCalendar September 2009

    This is an example showing a set of rules for a fictitious time
    zone where the first Daylight Time rule has an effective end date.
    There is a second Daylight Time rule that picks up where the other
    left off.
     BEGIN:VTIMEZONE
     TZID:Fictitious
     LAST-MODIFIED:19870101T000000Z
     BEGIN:STANDARD
     DTSTART:19671029T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19870405T020000
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:DAYLIGHT
     DTSTART:19990424T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=4
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

3.6.6. Alarm Component

 Component Name:  VALARM
 Purpose:  Provide a grouping of component properties that define an
    alarm.
 Format Definition:  A "VALARM" calendar component is defined by the
    following notation:
     alarmc     = "BEGIN" ":" "VALARM" CRLF
                  (audioprop / dispprop / emailprop)
                  "END" ":" "VALARM" CRLF
     audioprop  = *(
                ;
                ; 'action' and 'trigger' are both REQUIRED,

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                ; but MUST NOT occur more than once.
                ;
                action / trigger /
                ;
                ; 'duration' and 'repeat' are both OPTIONAL,
                ; and MUST NOT occur more than once each;
                ; but if one occurs, so MUST the other.
                ;
                duration / repeat /
                ;
                ; The following is OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                attach /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                x-prop / iana-prop
                ;
                )
     dispprop   = *(
                ;
                ; The following are REQUIRED,
                ; but MUST NOT occur more than once.
                ;
                action / description / trigger /
                ;
                ; 'duration' and 'repeat' are both OPTIONAL,
                ; and MUST NOT occur more than once each;
                ; but if one occurs, so MUST the other.
                ;
                duration / repeat /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                x-prop / iana-prop
                ;
                )
     emailprop  = *(
                ;
                ; The following are all REQUIRED,
                ; but MUST NOT occur more than once.
                ;
                action / description / trigger / summary /

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                ;
                ; The following is REQUIRED,
                ; and MAY occur more than once.
                ;
                attendee /
                ;
                ; 'duration' and 'repeat' are both OPTIONAL,
                ; and MUST NOT occur more than once each;
                ; but if one occurs, so MUST the other.
                ;
                duration / repeat /
                ;
                ; The following are OPTIONAL,
                ; and MAY occur more than once.
                ;
                attach / x-prop / iana-prop
                ;
                )
 Description:  A "VALARM" calendar component is a grouping of
    component properties that is a reminder or alarm for an event or a
    to-do.  For example, it may be used to define a reminder for a
    pending event or an overdue to-do.
    The "VALARM" calendar component MUST include the "ACTION" and
    "TRIGGER" properties.  The "ACTION" property further constrains
    the "VALARM" calendar component in the following ways:
    When the action is "AUDIO", the alarm can also include one and
    only one "ATTACH" property, which MUST point to a sound resource,
    which is rendered when the alarm is triggered.
    When the action is "DISPLAY", the alarm MUST also include a
    "DESCRIPTION" property, which contains the text to be displayed
    when the alarm is triggered.
    When the action is "EMAIL", the alarm MUST include a "DESCRIPTION"
    property, which contains the text to be used as the message body,
    a "SUMMARY" property, which contains the text to be used as the
    message subject, and one or more "ATTENDEE" properties, which
    contain the email address of attendees to receive the message.  It
    can also include one or more "ATTACH" properties, which are
    intended to be sent as message attachments.  When the alarm is
    triggered, the email message is sent.
    The "VALARM" calendar component MUST only appear within either a
    "VEVENT" or "VTODO" calendar component.  "VALARM" calendar
    components cannot be nested.  Multiple mutually independent

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    "VALARM" calendar components can be specified for a single
    "VEVENT" or "VTODO" calendar component.
    The "TRIGGER" property specifies when the alarm will be triggered.
    The "TRIGGER" property specifies a duration prior to the start of
    an event or a to-do.  The "TRIGGER" edge may be explicitly set to
    be relative to the "START" or "END" of the event or to-do with the
    "RELATED" parameter of the "TRIGGER" property.  The "TRIGGER"
    property value type can alternatively be set to an absolute
    calendar date with UTC time.
    In an alarm set to trigger on the "START" of an event or to-do,
    the "DTSTART" property MUST be present in the associated event or
    to-do.  In an alarm in a "VEVENT" calendar component set to
    trigger on the "END" of the event, either the "DTEND" property
    MUST be present, or the "DTSTART" and "DURATION" properties MUST
    both be present.  In an alarm in a "VTODO" calendar component set
    to trigger on the "END" of the to-do, either the "DUE" property
    MUST be present, or the "DTSTART" and "DURATION" properties MUST
    both be present.
    The alarm can be defined such that it triggers repeatedly.  A
    definition of an alarm with a repeating trigger MUST include both
    the "DURATION" and "REPEAT" properties.  The "DURATION" property
    specifies the delay period, after which the alarm will repeat.
    The "REPEAT" property specifies the number of additional
    repetitions that the alarm will be triggered.  This repetition
    count is in addition to the initial triggering of the alarm.  Both
    of these properties MUST be present in order to specify a
    repeating alarm.  If one of these two properties is absent, then
    the alarm will not repeat beyond the initial trigger.
    The "ACTION" property is used within the "VALARM" calendar
    component to specify the type of action invoked when the alarm is
    triggered.  The "VALARM" properties provide enough information for
    a specific action to be invoked.  It is typically the
    responsibility of a "Calendar User Agent" (CUA) to deliver the
    alarm in the specified fashion.  An "ACTION" property value of
    AUDIO specifies an alarm that causes a sound to be played to alert
    the user; DISPLAY specifies an alarm that causes a text message to
    be displayed to the user; and EMAIL specifies an alarm that causes
    an electronic email message to be delivered to one or more email
    addresses.
    In an AUDIO alarm, if the optional "ATTACH" property is included,
    it MUST specify an audio sound resource.  The intention is that
    the sound will be played as the alarm effect.  If an "ATTACH"
    property is specified that does not refer to a sound resource, or

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    if the specified sound resource cannot be rendered (because its
    format is unsupported, or because it cannot be retrieved), then
    the CUA or other entity responsible for playing the sound may
    choose a fallback action, such as playing a built-in default
    sound, or playing no sound at all.
    In a DISPLAY alarm, the intended alarm effect is for the text
    value of the "DESCRIPTION" property to be displayed to the user.
    In an EMAIL alarm, the intended alarm effect is for an email
    message to be composed and delivered to all the addresses
    specified by the "ATTENDEE" properties in the "VALARM" calendar
    component.  The "DESCRIPTION" property of the "VALARM" calendar
    component MUST be used as the body text of the message, and the
    "SUMMARY" property MUST be used as the subject text.  Any "ATTACH"
    properties in the "VALARM" calendar component SHOULD be sent as
    attachments to the message.
       Note: Implementations should carefully consider whether they
       accept alarm components from untrusted sources, e.g., when
       importing calendar objects from external sources.  One
       reasonable policy is to always ignore alarm components that the
       calendar user has not set herself, or at least ask for
       confirmation in such a case.
 Example:  The following example is for a "VALARM" calendar component
    that specifies an audio alarm that will sound at a precise time
    and repeat 4 more times at 15-minute intervals:
     BEGIN:VALARM
     TRIGGER;VALUE=DATE-TIME:19970317T133000Z
     REPEAT:4
     DURATION:PT15M
     ACTION:AUDIO
     ATTACH;FMTTYPE=audio/basic:ftp://example.com/pub/
      sounds/bell-01.aud
     END:VALARM
    The following example is for a "VALARM" calendar component that
    specifies a display alarm that will trigger 30 minutes before the
    scheduled start of the event or of the to-do it is associated with
    and will repeat 2 more times at 15-minute intervals:

Desruisseaux Standards Track [Page 75] RFC 5545 iCalendar September 2009

     BEGIN:VALARM
     TRIGGER:-PT30M
     REPEAT:2
     DURATION:PT15M
     ACTION:DISPLAY
     DESCRIPTION:Breakfast meeting with executive\n
      team at 8:30 AM EST.
     END:VALARM
    The following example is for a "VALARM" calendar component that
    specifies an email alarm that will trigger 2 days before the
    scheduled due DATE-TIME of a to-do with which it is associated.
    It does not repeat.  The email has a subject, body, and attachment
    link.
     BEGIN:VALARM
     TRIGGER;RELATED=END:-P2D
     ACTION:EMAIL
     ATTENDEE:mailto:john_doe@example.com
     SUMMARY:*** REMINDER: SEND AGENDA FOR WEEKLY STAFF MEETING ***
     DESCRIPTION:A draft agenda needs to be sent out to the attendees
       to the weekly managers meeting (MGR-LIST). Attached is a
       pointer the document template for the agenda file.
     ATTACH;FMTTYPE=application/msword:http://example.com/
      templates/agenda.doc
     END:VALARM

3.7. Calendar Properties

 The Calendar Properties are attributes that apply to the iCalendar
 object, as a whole.  These properties do not appear within a calendar
 component.  They SHOULD be specified after the "BEGIN:VCALENDAR"
 delimiter string and prior to any calendar component.

3.7.1. Calendar Scale

 Property Name:  CALSCALE
 Purpose:  This property defines the calendar scale used for the
    calendar information specified in the iCalendar object.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified once in an iCalendar
    object.  The default value is "GREGORIAN".

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 Description:  This memo is based on the Gregorian calendar scale.
    The Gregorian calendar scale is assumed if this property is not
    specified in the iCalendar object.  It is expected that other
    calendar scales will be defined in other specifications or by
    future versions of this memo.
 Format Definition:  This property is defined by the following
    notation:
     calscale   = "CALSCALE" calparam ":" calvalue CRLF
     calparam   = *(";" other-param)
     calvalue   = "GREGORIAN"
 Example:  The following is an example of this property:
     CALSCALE:GREGORIAN

3.7.2. Method

 Property Name:  METHOD
 Purpose:  This property defines the iCalendar object method
    associated with the calendar object.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified once in an iCalendar
    object.
 Description:  When used in a MIME message entity, the value of this
    property MUST be the same as the Content-Type "method" parameter
    value.  If either the "METHOD" property or the Content-Type
    "method" parameter is specified, then the other MUST also be
    specified.
    No methods are defined by this specification.  This is the subject
    of other specifications, such as the iCalendar Transport-
    independent Interoperability Protocol (iTIP) defined by [2446bis].
    If this property is not present in the iCalendar object, then a
    scheduling transaction MUST NOT be assumed.  In such cases, the
    iCalendar object is merely being used to transport a snapshot of

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    some calendar information; without the intention of conveying a
    scheduling semantic.
 Format Definition:  This property is defined by the following
    notation:
     method     = "METHOD" metparam ":" metvalue CRLF
     metparam   = *(";" other-param)
     metvalue   = iana-token
 Example:  The following is a hypothetical example of this property to
    convey that the iCalendar object is a scheduling request:
     METHOD:REQUEST

3.7.3. Product Identifier

 Property Name:  PRODID
 Purpose:  This property specifies the identifier for the product that
    created the iCalendar object.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  The property MUST be specified once in an iCalendar
    object.
 Description:  The vendor of the implementation SHOULD assure that
    this is a globally unique identifier; using some technique such as
    an FPI value, as defined in [ISO.9070.1991].
    This property SHOULD NOT be used to alter the interpretation of an
    iCalendar object beyond the semantics specified in this memo.  For
    example, it is not to be used to further the understanding of non-
    standard properties.
 Format Definition:  This property is defined by the following
    notation:
     prodid     = "PRODID" pidparam ":" pidvalue CRLF
     pidparam   = *(";" other-param)

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     pidvalue   = text
     ;Any text that describes the product and version
     ;and that is generally assured of being unique.
 Example:  The following is an example of this property.  It does not
    imply that English is the default language.
     PRODID:-//ABC Corporation//NONSGML My Product//EN

3.7.4. Version

 Property Name:  VERSION
 Purpose:  This property specifies the identifier corresponding to the
    highest version number or the minimum and maximum range of the
    iCalendar specification that is required in order to interpret the
    iCalendar object.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property MUST be specified once in an iCalendar
    object.
 Description:  A value of "2.0" corresponds to this memo.
 Format Definition:  This property is defined by the following
    notation:
     version    = "VERSION" verparam ":" vervalue CRLF
     verparam   = *(";" other-param)
     vervalue   = "2.0"         ;This memo
                / maxver
                / (minver ";" maxver)
     minver     = <A IANA-registered iCalendar version identifier>
     ;Minimum iCalendar version needed to parse the iCalendar object.
     maxver     = <A IANA-registered iCalendar version identifier>
     ;Maximum iCalendar version needed to parse the iCalendar object.

Desruisseaux Standards Track [Page 79] RFC 5545 iCalendar September 2009

 Example:  The following is an example of this property:
     VERSION:2.0

3.8. Component Properties

 The following properties can appear within calendar components, as
 specified by each component property definition.

3.8.1. Descriptive Component Properties

 The following properties specify descriptive information about
 calendar components.

3.8.1.1. Attachment

 Property Name:  ATTACH
 Purpose:  This property provides the capability to associate a
    document object with a calendar component.
 Value Type:  The default value type for this property is URI.  The
    value type can also be set to BINARY to indicate inline binary
    encoded content information.
 Property Parameters:  IANA, non-standard, inline encoding, and value
    data type property parameters can be specified on this property.
    The format type parameter can be specified on this property and is
    RECOMMENDED for inline binary encoded content information.
 Conformance:  This property can be specified multiple times in a
    "VEVENT", "VTODO", "VJOURNAL", or "VALARM" calendar component with
    the exception of AUDIO alarm that only allows this property to
    occur once.
 Description:  This property is used in "VEVENT", "VTODO", and
    "VJOURNAL" calendar components to associate a resource (e.g.,
    document) with the calendar component.  This property is used in
    "VALARM" calendar components to specify an audio sound resource or
    an email message attachment.  This property can be specified as a
    URI pointing to a resource or as inline binary encoded content.
    When this property is specified as inline binary encoded content,
    calendar applications MAY attempt to guess the media type of the
    resource via inspection of its content if and only if the media
    type of the resource is not given by the "FMTTYPE" parameter.  If
    the media type remains unknown, calendar applications SHOULD treat
    it as type "application/octet-stream".

Desruisseaux Standards Track [Page 80] RFC 5545 iCalendar September 2009

 Format Definition:  This property is defined by the following
    notation:
     attach     = "ATTACH" attachparam ( ":" uri ) /
                  (
                    ";" "ENCODING" "=" "BASE64"
                    ";" "VALUE" "=" "BINARY"
                    ":" binary
                  )
                  CRLF
     attachparam = *(
                 ;
                 ; The following is OPTIONAL for a URI value,
                 ; RECOMMENDED for a BINARY value,
                 ; and MUST NOT occur more than once.
                 ;
                 (";" fmttypeparam) /
                 ;
                 ; The following is OPTIONAL,
                 ; and MAY occur more than once.
                 ;
                 (";" other-param)
                 ;
                 )
 Example:  The following are examples of this property:
     ATTACH:CID:jsmith.part3.960817T083000.xyzMail@example.com
     ATTACH;FMTTYPE=application/postscript:ftp://example.com/pub/
      reports/r-960812.ps

3.8.1.2. Categories

 Property Name:  CATEGORIES
 Purpose:  This property defines the categories for a calendar
    component.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, and language property
    parameters can be specified on this property.
 Conformance:  The property can be specified within "VEVENT", "VTODO",
    or "VJOURNAL" calendar components.

Desruisseaux Standards Track [Page 81] RFC 5545 iCalendar September 2009

 Description:  This property is used to specify categories or subtypes
    of the calendar component.  The categories are useful in searching
    for a calendar component of a particular type and category.
    Within the "VEVENT", "VTODO", or "VJOURNAL" calendar components,
    more than one category can be specified as a COMMA-separated list
    of categories.
 Format Definition:  This property is defined by the following
    notation:
     categories = "CATEGORIES" catparam ":" text *("," text)
                  CRLF
     catparam   = *(
                ;
                ; The following is OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" languageparam ) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following are examples of this property:
     CATEGORIES:APPOINTMENT,EDUCATION
     CATEGORIES:MEETING

3.8.1.3. Classification

 Property Name:  CLASS
 Purpose:  This property defines the access classification for a
    calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  The property can be specified once in a "VEVENT",
    "VTODO", or "VJOURNAL" calendar components.

Desruisseaux Standards Track [Page 82] RFC 5545 iCalendar September 2009

 Description:  An access classification is only one component of the
    general security system within a calendar application.  It
    provides a method of capturing the scope of the access the
    calendar owner intends for information within an individual
    calendar entry.  The access classification of an individual
    iCalendar component is useful when measured along with the other
    security components of a calendar system (e.g., calendar user
    authentication, authorization, access rights, access role, etc.).
    Hence, the semantics of the individual access classifications
    cannot be completely defined by this memo alone.  Additionally,
    due to the "blind" nature of most exchange processes using this
    memo, these access classifications cannot serve as an enforcement
    statement for a system receiving an iCalendar object.  Rather,
    they provide a method for capturing the intention of the calendar
    owner for the access to the calendar component.  If not specified
    in a component that allows this property, the default value is
    PUBLIC.  Applications MUST treat x-name and iana-token values they
    don't recognize the same way as they would the PRIVATE value.
 Format Definition:  This property is defined by the following
    notation:
     class      = "CLASS" classparam ":" classvalue CRLF
     classparam = *(";" other-param)
     classvalue = "PUBLIC" / "PRIVATE" / "CONFIDENTIAL" / iana-token
                / x-name
     ;Default is PUBLIC
 Example:  The following is an example of this property:
     CLASS:PUBLIC

3.8.1.4. Comment

 Property Name:  COMMENT
 Purpose:  This property specifies non-processing information intended
    to provide a comment to the calendar user.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, alternate text
    representation, and language property parameters can be specified
    on this property.

Desruisseaux Standards Track [Page 83] RFC 5545 iCalendar September 2009

 Conformance:  This property can be specified multiple times in
    "VEVENT", "VTODO", "VJOURNAL", and "VFREEBUSY" calendar components
    as well as in the "STANDARD" and "DAYLIGHT" sub-components.
 Description:  This property is used to specify a comment to the
    calendar user.
 Format Definition:  This property is defined by the following
    notation:
     comment    = "COMMENT" commparam ":" text CRLF
     commparam  = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" altrepparam) / (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following is an example of this property:
     COMMENT:The meeting really needs to include both ourselves
       and the customer. We can't hold this meeting without them.
       As a matter of fact\, the venue for the meeting ought to be at
       their site. - - John

3.8.1.5. Description

 Property Name:  DESCRIPTION
 Purpose:  This property provides a more complete description of the
    calendar component than that provided by the "SUMMARY" property.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, alternate text
    representation, and language property parameters can be specified
    on this property.

Desruisseaux Standards Track [Page 84] RFC 5545 iCalendar September 2009

 Conformance:  The property can be specified in the "VEVENT", "VTODO",
    "VJOURNAL", or "VALARM" calendar components.  The property can be
    specified multiple times only within a "VJOURNAL" calendar
    component.
 Description:  This property is used in the "VEVENT" and "VTODO" to
    capture lengthy textual descriptions associated with the activity.
    This property is used in the "VJOURNAL" calendar component to
    capture one or more textual journal entries.
    This property is used in the "VALARM" calendar component to
    capture the display text for a DISPLAY category of alarm, and to
    capture the body text for an EMAIL category of alarm.
 Format Definition:  This property is defined by the following
    notation:
     description = "DESCRIPTION" descparam ":" text CRLF
     descparam   = *(
                 ;
                 ; The following are OPTIONAL,
                 ; but MUST NOT occur more than once.
                 ;
                 (";" altrepparam) / (";" languageparam) /
                 ;
                 ; The following is OPTIONAL,
                 ; and MAY occur more than once.
                 ;
                 (";" other-param)
                 ;
                 )
 Example:  The following is an example of this property with formatted
    line breaks in the property value:
     DESCRIPTION:Meeting to provide technical review for "Phoenix"
       design.\nHappy Face Conference Room. Phoenix design team
       MUST attend this meeting.\nRSVP to team leader.

3.8.1.6. Geographic Position

 Property Name:  GEO
 Purpose:  This property specifies information related to the global
    position for the activity specified by a calendar component.

Desruisseaux Standards Track [Page 85] RFC 5545 iCalendar September 2009

 Value Type:  FLOAT.  The value MUST be two SEMICOLON-separated FLOAT
    values.
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in "VEVENT" or "VTODO"
    calendar components.
 Description:  This property value specifies latitude and longitude,
    in that order (i.e., "LAT LON" ordering).  The longitude
    represents the location east or west of the prime meridian as a
    positive or negative real number, respectively.  The longitude and
    latitude values MAY be specified up to six decimal places, which
    will allow for accuracy to within one meter of geographical
    position.  Receiving applications MUST accept values of this
    precision and MAY truncate values of greater precision.
    Values for latitude and longitude shall be expressed as decimal
    fractions of degrees.  Whole degrees of latitude shall be
    represented by a two-digit decimal number ranging from 0 through
    90.  Whole degrees of longitude shall be represented by a decimal
    number ranging from 0 through 180.  When a decimal fraction of a
    degree is specified, it shall be separated from the whole number
    of degrees by a decimal point.
    Latitudes north of the equator shall be specified by a plus sign
    (+), or by the absence of a minus sign (-), preceding the digits
    designating degrees.  Latitudes south of the Equator shall be
    designated by a minus sign (-) preceding the digits designating
    degrees.  A point on the Equator shall be assigned to the Northern
    Hemisphere.
    Longitudes east of the prime meridian shall be specified by a plus
    sign (+), or by the absence of a minus sign (-), preceding the
    digits designating degrees.  Longitudes west of the meridian shall
    be designated by minus sign (-) preceding the digits designating
    degrees.  A point on the prime meridian shall be assigned to the
    Eastern Hemisphere.  A point on the 180th meridian shall be
    assigned to the Western Hemisphere.  One exception to this last
    convention is permitted.  For the special condition of describing
    a band of latitude around the earth, the East Bounding Coordinate
    data element shall be assigned the value +180 (180) degrees.
    Any spatial address with a latitude of +90 (90) or -90 degrees
    will specify the position at the North or South Pole,
    respectively.  The component for longitude may have any legal
    value.

Desruisseaux Standards Track [Page 86] RFC 5545 iCalendar September 2009

    With the exception of the special condition described above, this
    form is specified in [ANSI INCITS 61-1986].
    The simple formula for converting degrees-minutes-seconds into
    decimal degrees is:
    decimal = degrees + minutes/60 + seconds/3600.
 Format Definition:  This property is defined by the following
    notation:
     geo        = "GEO" geoparam ":" geovalue CRLF
     geoparam   = *(";" other-param)
     geovalue   = float ";" float
     ;Latitude and Longitude components
 Example:  The following is an example of this property:
     GEO:37.386013;-122.082932

3.8.1.7. Location

 Property Name:  LOCATION
 Purpose:  This property defines the intended venue for the activity
    defined by a calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, alternate text
    representation, and language property parameters can be specified
    on this property.
 Conformance:  This property can be specified in "VEVENT" or "VTODO"
    calendar component.
 Description:  Specific venues such as conference or meeting rooms may
    be explicitly specified using this property.  An alternate
    representation may be specified that is a URI that points to
    directory information with more structured specification of the
    location.  For example, the alternate representation may specify
    either an LDAP URL [RFC4516] pointing to an LDAP server entry or a
    CID URL [RFC2392] pointing to a MIME body part containing a
    Virtual-Information Card (vCard) [RFC2426] for the location.

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 Format Definition:  This property is defined by the following
    notation:
     location   = "LOCATION"  locparam ":" text CRLF
     locparam   = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" altrepparam) / (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following are some examples of this property:
     LOCATION:Conference Room - F123\, Bldg. 002
     LOCATION;ALTREP="http://xyzcorp.com/conf-rooms/f123.vcf":
      Conference Room - F123\, Bldg. 002

3.8.1.8. Percent Complete

 Property Name:  PERCENT-COMPLETE
 Purpose:  This property is used by an assignee or delegatee of a
    to-do to convey the percent completion of a to-do to the
    "Organizer".
 Value Type:  INTEGER
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified once in a "VTODO"
    calendar component.
 Description:  The property value is a positive integer between 0 and
    100.  A value of "0" indicates the to-do has not yet been started.
    A value of "100" indicates that the to-do has been completed.
    Integer values in between indicate the percent partially complete.

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    When a to-do is assigned to multiple individuals, the property
    value indicates the percent complete for that portion of the to-do
    assigned to the assignee or delegatee.  For example, if a to-do is
    assigned to both individuals "A" and "B".  A reply from "A" with a
    percent complete of "70" indicates that "A" has completed 70% of
    the to-do assigned to them.  A reply from "B" with a percent
    complete of "50" indicates "B" has completed 50% of the to-do
    assigned to them.
 Format Definition:  This property is defined by the following
    notation:
     percent = "PERCENT-COMPLETE" pctparam ":" integer CRLF
     pctparam   = *(";" other-param)
 Example:  The following is an example of this property to show 39%
    completion:
     PERCENT-COMPLETE:39

3.8.1.9. Priority

 Property Name:  PRIORITY
 Purpose:  This property defines the relative priority for a calendar
    component.
 Value Type:  INTEGER
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in "VEVENT" and "VTODO"
    calendar components.
 Description:  This priority is specified as an integer in the range 0
    to 9.  A value of 0 specifies an undefined priority.  A value of 1
    is the highest priority.  A value of 2 is the second highest
    priority.  Subsequent numbers specify a decreasing ordinal
    priority.  A value of 9 is the lowest priority.
    A CUA with a three-level priority scheme of "HIGH", "MEDIUM", and
    "LOW" is mapped into this property such that a property value in
    the range of 1 to 4 specifies "HIGH" priority.  A value of 5 is
    the normal or "MEDIUM" priority.  A value in the range of 6 to 9
    is "LOW" priority.

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    A CUA with a priority schema of "A1", "A2", "A3", "B1", "B2", ...,
    "C3" is mapped into this property such that a property value of 1
    specifies "A1", a property value of 2 specifies "A2", a property
    value of 3 specifies "A3", and so forth up to a property value of
    9 specifies "C3".
    Other integer values are reserved for future use.
    Within a "VEVENT" calendar component, this property specifies a
    priority for the event.  This property may be useful when more
    than one event is scheduled for a given time period.
    Within a "VTODO" calendar component, this property specified a
    priority for the to-do.  This property is useful in prioritizing
    multiple action items for a given time period.
 Format Definition:  This property is defined by the following
    notation:
     priority   = "PRIORITY" prioparam ":" priovalue CRLF
     ;Default is zero (i.e., undefined).
     prioparam  = *(";" other-param)
     priovalue   = integer       ;Must be in the range [0..9]
        ; All other values are reserved for future use.
 Example:  The following is an example of a property with the highest
    priority:
     PRIORITY:1
    The following is an example of a property with a next highest
    priority:
     PRIORITY:2
    The following is an example of a property with no priority.  This
    is equivalent to not specifying the "PRIORITY" property:
     PRIORITY:0

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3.8.1.10. Resources

 Property Name:  RESOURCES
 Purpose:  This property defines the equipment or resources
    anticipated for an activity specified by a calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, alternate text
    representation, and language property parameters can be specified
    on this property.
 Conformance:  This property can be specified once in "VEVENT" or
    "VTODO" calendar component.
 Description:  The property value is an arbitrary text.  More than one
    resource can be specified as a COMMA-separated list of resources.
 Format Definition:  This property is defined by the following
    notation:
     resources  = "RESOURCES" resrcparam ":" text *("," text) CRLF
     resrcparam = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" altrepparam) / (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following is an example of this property:
     RESOURCES:EASEL,PROJECTOR,VCR
     RESOURCES;LANGUAGE=fr:Nettoyeur haute pression

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3.8.1.11. Status

 Property Name:  STATUS
 Purpose:  This property defines the overall status or confirmation
    for the calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified once in "VEVENT",
    "VTODO", or "VJOURNAL" calendar components.
 Description:  In a group-scheduled calendar component, the property
    is used by the "Organizer" to provide a confirmation of the event
    to the "Attendees".  For example in a "VEVENT" calendar component,
    the "Organizer" can indicate that a meeting is tentative,
    confirmed, or cancelled.  In a "VTODO" calendar component, the
    "Organizer" can indicate that an action item needs action, is
    completed, is in process or being worked on, or has been
    cancelled.  In a "VJOURNAL" calendar component, the "Organizer"
    can indicate that a journal entry is draft, final, or has been
    cancelled or removed.
 Format Definition:  This property is defined by the following
    notation:
     status          = "STATUS" statparam ":" statvalue CRLF
     statparam       = *(";" other-param)
     statvalue       = (statvalue-event
                     /  statvalue-todo
                     /  statvalue-jour)
     statvalue-event = "TENTATIVE"    ;Indicates event is tentative.
                     / "CONFIRMED"    ;Indicates event is definite.
                     / "CANCELLED"    ;Indicates event was cancelled.
     ;Status values for a "VEVENT"
     statvalue-todo  = "NEEDS-ACTION" ;Indicates to-do needs action.
                     / "COMPLETED"    ;Indicates to-do completed.
                     / "IN-PROCESS"   ;Indicates to-do in process of.
                     / "CANCELLED"    ;Indicates to-do was cancelled.
     ;Status values for "VTODO".

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     statvalue-jour  = "DRAFT"        ;Indicates journal is draft.
                     / "FINAL"        ;Indicates journal is final.
                     / "CANCELLED"    ;Indicates journal is removed.
    ;Status values for "VJOURNAL".
 Example:  The following is an example of this property for a "VEVENT"
    calendar component:
     STATUS:TENTATIVE
    The following is an example of this property for a "VTODO"
    calendar component:
     STATUS:NEEDS-ACTION
    The following is an example of this property for a "VJOURNAL"
    calendar component:
     STATUS:DRAFT

3.8.1.12. Summary

 Property Name:  SUMMARY
 Purpose:  This property defines a short summary or subject for the
    calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, alternate text
    representation, and language property parameters can be specified
    on this property.
 Conformance:  The property can be specified in "VEVENT", "VTODO",
    "VJOURNAL", or "VALARM" calendar components.
 Description:  This property is used in the "VEVENT", "VTODO", and
    "VJOURNAL" calendar components to capture a short, one-line
    summary about the activity or journal entry.
    This property is used in the "VALARM" calendar component to
    capture the subject of an EMAIL category of alarm.
 Format Definition:  This property is defined by the following
    notation:

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     summary    = "SUMMARY" summparam ":" text CRLF
     summparam  = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" altrepparam) / (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following is an example of this property:
     SUMMARY:Department Party

3.8.2. Date and Time Component Properties

 The following properties specify date and time related information in
 calendar components.

3.8.2.1. Date-Time Completed

 Property Name:  COMPLETED
 Purpose:  This property defines the date and time that a to-do was
    actually completed.
 Value Type:  DATE-TIME
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  The property can be specified in a "VTODO" calendar
    component.  The value MUST be specified as a date with UTC time.
 Description:  This property defines the date and time that a to-do
    was actually completed.
 Format Definition:  This property is defined by the following
    notation:

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     completed  = "COMPLETED" compparam ":" date-time CRLF
     compparam  = *(";" other-param)
 Example:  The following is an example of this property:
  COMPLETED:19960401T150000Z

3.8.2.2. Date-Time End

 Property Name:  DTEND
 Purpose:  This property specifies the date and time that a calendar
    component ends.
 Value Type:  The default value type is DATE-TIME.  The value type can
    be set to a DATE value type.
 Property Parameters:  IANA, non-standard, value data type, and time
    zone identifier property parameters can be specified on this
    property.
 Conformance:  This property can be specified in "VEVENT" or
    "VFREEBUSY" calendar components.
 Description:  Within the "VEVENT" calendar component, this property
    defines the date and time by which the event ends.  The value type
    of this property MUST be the same as the "DTSTART" property, and
    its value MUST be later in time than the value of the "DTSTART"
    property.  Furthermore, this property MUST be specified as a date
    with local time if and only if the "DTSTART" property is also
    specified as a date with local time.
    Within the "VFREEBUSY" calendar component, this property defines
    the end date and time for the free or busy time information.  The
    time MUST be specified in the UTC time format.  The value MUST be
    later in time than the value of the "DTSTART" property.
 Format Definition:  This property is defined by the following
    notation:

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     dtend      = "DTEND" dtendparam ":" dtendval CRLF
     dtendparam = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                (";" tzidparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     dtendval   = date-time / date
     ;Value MUST match value type
 Example:  The following is an example of this property:
     DTEND:19960401T150000Z
     DTEND;VALUE=DATE:19980704

3.8.2.3. Date-Time Due

 Property Name:  DUE
 Purpose:  This property defines the date and time that a to-do is
    expected to be completed.
 Value Type:  The default value type is DATE-TIME.  The value type can
    be set to a DATE value type.
 Property Parameters:  IANA, non-standard, value data type, and time
    zone identifier property parameters can be specified on this
    property.
 Conformance:  The property can be specified once in a "VTODO"
    calendar component.
 Description:  This property defines the date and time before which a
    to-do is expected to be completed.  For cases where this property
    is specified in a "VTODO" calendar component that also specifies a
    "DTSTART" property, the value type of this property MUST be the
    same as the "DTSTART" property, and the value of this property

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    MUST be later in time than the value of the "DTSTART" property.
    Furthermore, this property MUST be specified as a date with local
    time if and only if the "DTSTART" property is also specified as a
    date with local time.
 Format Definition:  This property is defined by the following
    notation:
     due        = "DUE" dueparam ":" dueval CRLF
     dueparam   = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                (";" tzidparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     dueval     = date-time / date
     ;Value MUST match value type
 Example:  The following is an example of this property:
     DUE:19980430T000000Z

3.8.2.4. Date-Time Start

 Property Name:  DTSTART
 Purpose:  This property specifies when the calendar component begins.
 Value Type:  The default value type is DATE-TIME.  The time value
    MUST be one of the forms defined for the DATE-TIME value type.
    The value type can be set to a DATE value type.
 Property Parameters:  IANA, non-standard, value data type, and time
    zone identifier property parameters can be specified on this
    property.
 Conformance:  This property can be specified once in the "VEVENT",
    "VTODO", or "VFREEBUSY" calendar components as well as in the

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    "STANDARD" and "DAYLIGHT" sub-components.  This property is
    REQUIRED in all types of recurring calendar components that
    specify the "RRULE" property.  This property is also REQUIRED in
    "VEVENT" calendar components contained in iCalendar objects that
    don't specify the "METHOD" property.
 Description:  Within the "VEVENT" calendar component, this property
    defines the start date and time for the event.
    Within the "VFREEBUSY" calendar component, this property defines
    the start date and time for the free or busy time information.
    The time MUST be specified in UTC time.
    Within the "STANDARD" and "DAYLIGHT" sub-components, this property
    defines the effective start date and time for a time zone
    specification.  This property is REQUIRED within each "STANDARD"
    and "DAYLIGHT" sub-components included in "VTIMEZONE" calendar
    components and MUST be specified as a date with local time without
    the "TZID" property parameter.
 Format Definition:  This property is defined by the following
    notation:
     dtstart    = "DTSTART" dtstparam ":" dtstval CRLF
     dtstparam  = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                (";" tzidparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     dtstval    = date-time / date
     ;Value MUST match value type
 Example:  The following is an example of this property:
     DTSTART:19980118T073000Z

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3.8.2.5. Duration

 Property Name:  DURATION
 Purpose:  This property specifies a positive duration of time.
 Value Type:  DURATION
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in "VEVENT", "VTODO", or
    "VALARM" calendar components.
 Description:  In a "VEVENT" calendar component the property may be
    used to specify a duration of the event, instead of an explicit
    end DATE-TIME.  In a "VTODO" calendar component the property may
    be used to specify a duration for the to-do, instead of an
    explicit due DATE-TIME.  In a "VALARM" calendar component the
    property may be used to specify the delay period prior to
    repeating an alarm.  When the "DURATION" property relates to a
    "DTSTART" property that is specified as a DATE value, then the
    "DURATION" property MUST be specified as a "dur-day" or "dur-week"
    value.
 Format Definition:  This property is defined by the following
    notation:
     duration   = "DURATION" durparam ":" dur-value CRLF
                  ;consisting of a positive duration of time.
     durparam   = *(";" other-param)
 Example:  The following is an example of this property that specifies
    an interval of time of one hour and zero minutes and zero seconds:
     DURATION:PT1H0M0S
    The following is an example of this property that specifies an
    interval of time of 15 minutes.
     DURATION:PT15M

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3.8.2.6. Free/Busy Time

 Property Name:  FREEBUSY
 Purpose:  This property defines one or more free or busy time
    intervals.
 Value Type:  PERIOD
 Property Parameters:  IANA, non-standard, and free/busy time type
    property parameters can be specified on this property.
 Conformance:  The property can be specified in a "VFREEBUSY" calendar
    component.
 Description:  These time periods can be specified as either a start
    and end DATE-TIME or a start DATE-TIME and DURATION.  The date and
    time MUST be a UTC time format.
    "FREEBUSY" properties within the "VFREEBUSY" calendar component
    SHOULD be sorted in ascending order, based on start time and then
    end time, with the earliest periods first.
    The "FREEBUSY" property can specify more than one value, separated
    by the COMMA character.  In such cases, the "FREEBUSY" property
    values MUST all be of the same "FBTYPE" property parameter type
    (e.g., all values of a particular "FBTYPE" listed together in a
    single property).
 Format Definition:  This property is defined by the following
    notation:
     freebusy   = "FREEBUSY" fbparam ":" fbvalue CRLF
     fbparam    = *(
                ;
                ; The following is OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" fbtypeparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )

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     fbvalue    = period *("," period)
     ;Time value MUST be in the UTC time format.
 Example:  The following are some examples of this property:
     FREEBUSY;FBTYPE=BUSY-UNAVAILABLE:19970308T160000Z/PT8H30M
     FREEBUSY;FBTYPE=FREE:19970308T160000Z/PT3H,19970308T200000Z/PT1H
     FREEBUSY;FBTYPE=FREE:19970308T160000Z/PT3H,19970308T200000Z/PT1H
      ,19970308T230000Z/19970309T000000Z

3.8.2.7. Time Transparency

 Property Name:  TRANSP
 Purpose:  This property defines whether or not an event is
    transparent to busy time searches.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified once in a "VEVENT"
    calendar component.
 Description:  Time Transparency is the characteristic of an event
    that determines whether it appears to consume time on a calendar.
    Events that consume actual time for the individual or resource
    associated with the calendar SHOULD be recorded as OPAQUE,
    allowing them to be detected by free/busy time searches.  Other
    events, which do not take up the individual's (or resource's) time
    SHOULD be recorded as TRANSPARENT, making them invisible to free/
    busy time searches.
 Format Definition:  This property is defined by the following
    notation:
     transp     = "TRANSP" transparam ":" transvalue CRLF
     transparam = *(";" other-param)
     transvalue = "OPAQUE"
                 ;Blocks or opaque on busy time searches.
                 / "TRANSPARENT"
                 ;Transparent on busy time searches.
     ;Default value is OPAQUE

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 Example:  The following is an example of this property for an event
    that is transparent or does not block on free/busy time searches:
     TRANSP:TRANSPARENT
    The following is an example of this property for an event that is
    opaque or blocks on free/busy time searches:
     TRANSP:OPAQUE

3.8.3. Time Zone Component Properties

 The following properties specify time zone information in calendar
 components.

3.8.3.1. Time Zone Identifier

 Property Name:  TZID
 Purpose:  This property specifies the text value that uniquely
    identifies the "VTIMEZONE" calendar component in the scope of an
    iCalendar object.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property MUST be specified in a "VTIMEZONE"
    calendar component.
 Description:  This is the label by which a time zone calendar
    component is referenced by any iCalendar properties whose value
    type is either DATE-TIME or TIME and not intended to specify a UTC
    or a "floating" time.  The presence of the SOLIDUS character as a
    prefix, indicates that this "TZID" represents an unique ID in a
    globally defined time zone registry (when such registry is
    defined).
       Note: This document does not define a naming convention for
       time zone identifiers.  Implementers may want to use the naming
       conventions defined in existing time zone specifications such
       as the public-domain TZ database [TZDB].  The specification of
       globally unique time zone identifiers is not addressed by this
       document and is left for future study.

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 Format Definition:  This property is defined by the following
    notation:
     tzid       = "TZID" tzidpropparam ":" [tzidprefix] text CRLF
     tzidpropparam      = *(";" other-param)
     ;tzidprefix        = "/"
     ; Defined previously. Just listed here for reader convenience.
 Example:  The following are examples of non-globally unique time zone
    identifiers:
     TZID:America/New_York
     TZID:America/Los_Angeles
    The following is an example of a fictitious globally unique time
    zone identifier:
     TZID:/example.org/America/New_York

3.8.3.2. Time Zone Name

 Property Name:  TZNAME
 Purpose:  This property specifies the customary designation for a
    time zone description.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, and language property
    parameters can be specified on this property.
 Conformance:  This property can be specified in "STANDARD" and
    "DAYLIGHT" sub-components.
 Description:  This property specifies a customary name that can be
    used when displaying dates that occur during the observance
    defined by the time zone sub-component.
 Format Definition:  This property is defined by the following
    notation:

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     tzname     = "TZNAME" tznparam ":" text CRLF
     tznparam   = *(
                ;
                ; The following is OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following are examples of this property:
     TZNAME:EST
     TZNAME;LANGUAGE=fr-CA:HNE

3.8.3.3. Time Zone Offset From

 Property Name:  TZOFFSETFROM
 Purpose:  This property specifies the offset that is in use prior to
    this time zone observance.
 Value Type:  UTC-OFFSET
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property MUST be specified in "STANDARD" and
    "DAYLIGHT" sub-components.
 Description:  This property specifies the offset that is in use prior
    to this time observance.  It is used to calculate the absolute
    time at which the transition to a given observance takes place.
    This property MUST only be specified in a "VTIMEZONE" calendar
    component.  A "VTIMEZONE" calendar component MUST include this
    property.  The property value is a signed numeric indicating the
    number of hours and possibly minutes from UTC.  Positive numbers
    represent time zones east of the prime meridian, or ahead of UTC.
    Negative numbers represent time zones west of the prime meridian,
    or behind UTC.

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 Format Definition:  This property is defined by the following
    notation:
     tzoffsetfrom       = "TZOFFSETFROM" frmparam ":" utc-offset
                          CRLF
     frmparam   = *(";" other-param)
 Example:  The following are examples of this property:
     TZOFFSETFROM:-0500
     TZOFFSETFROM:+1345

3.8.3.4. Time Zone Offset To

 Property Name:  TZOFFSETTO
 Purpose:  This property specifies the offset that is in use in this
    time zone observance.
 Value Type:  UTC-OFFSET
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property MUST be specified in "STANDARD" and
    "DAYLIGHT" sub-components.
 Description:  This property specifies the offset that is in use in
    this time zone observance.  It is used to calculate the absolute
    time for the new observance.  The property value is a signed
    numeric indicating the number of hours and possibly minutes from
    UTC.  Positive numbers represent time zones east of the prime
    meridian, or ahead of UTC.  Negative numbers represent time zones
    west of the prime meridian, or behind UTC.
 Format Definition:  This property is defined by the following
    notation:
     tzoffsetto = "TZOFFSETTO" toparam ":" utc-offset CRLF
     toparam    = *(";" other-param)

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 Example:  The following are examples of this property:
     TZOFFSETTO:-0400
     TZOFFSETTO:+1245

3.8.3.5. Time Zone URL

 Property Name:  TZURL
 Purpose:  This property provides a means for a "VTIMEZONE" component
    to point to a network location that can be used to retrieve an up-
    to-date version of itself.
 Value Type:  URI
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in a "VTIMEZONE"
    calendar component.
 Description:  This property provides a means for a "VTIMEZONE"
    component to point to a network location that can be used to
    retrieve an up-to-date version of itself.  This provides a hook to
    handle changes government bodies impose upon time zone
    definitions.  Retrieval of this resource results in an iCalendar
    object containing a single "VTIMEZONE" component and a "METHOD"
    property set to PUBLISH.
 Format Definition:  This property is defined by the following
    notation:
     tzurl      = "TZURL" tzurlparam ":" uri CRLF
     tzurlparam = *(";" other-param)
 Example:  The following is an example of this property:
  TZURL:http://timezones.example.org/tz/America-Los_Angeles.ics

3.8.4. Relationship Component Properties

 The following properties specify relationship information in calendar
 components.

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3.8.4.1. Attendee

 Property Name:  ATTENDEE
 Purpose:  This property defines an "Attendee" within a calendar
    component.
 Value Type:  CAL-ADDRESS
 Property Parameters:  IANA, non-standard, language, calendar user
    type, group or list membership, participation role, participation
    status, RSVP expectation, delegatee, delegator, sent by, common
    name, or directory entry reference property parameters can be
    specified on this property.
 Conformance:  This property MUST be specified in an iCalendar object
    that specifies a group-scheduled calendar entity.  This property
    MUST NOT be specified in an iCalendar object when publishing the
    calendar information (e.g., NOT in an iCalendar object that
    specifies the publication of a calendar user's busy time, event,
    to-do, or journal).  This property is not specified in an
    iCalendar object that specifies only a time zone definition or
    that defines calendar components that are not group-scheduled
    components, but are components only on a single user's calendar.
 Description:  This property MUST only be specified within calendar
    components to specify participants, non-participants, and the
    chair of a group-scheduled calendar entity.  The property is
    specified within an "EMAIL" category of the "VALARM" calendar
    component to specify an email address that is to receive the email
    type of iCalendar alarm.
    The property parameter "CN" is for the common or displayable name
    associated with the calendar address; "ROLE", for the intended
    role that the attendee will have in the calendar component;
    "PARTSTAT", for the status of the attendee's participation;
    "RSVP", for indicating whether the favor of a reply is requested;
    "CUTYPE", to indicate the type of calendar user; "MEMBER", to
    indicate the groups that the attendee belongs to; "DELEGATED-TO",
    to indicate the calendar users that the original request was
    delegated to; and "DELEGATED-FROM", to indicate whom the request
    was delegated from; "SENT-BY", to indicate whom is acting on
    behalf of the "ATTENDEE"; and "DIR", to indicate the URI that
    points to the directory information corresponding to the attendee.
    These property parameters can be specified on an "ATTENDEE"
    property in either a "VEVENT", "VTODO", or "VJOURNAL" calendar
    component.  They MUST NOT be specified in an "ATTENDEE" property
    in a "VFREEBUSY" or "VALARM" calendar component.  If the

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    "LANGUAGE" property parameter is specified, the identified
    language applies to the "CN" parameter.
    A recipient delegated a request MUST inherit the "RSVP" and "ROLE"
    values from the attendee that delegated the request to them.
    Multiple attendees can be specified by including multiple
    "ATTENDEE" properties within the calendar component.
 Format Definition:  This property is defined by the following
    notation:
     attendee   = "ATTENDEE" attparam ":" cal-address CRLF
     attparam   = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" cutypeparam) / (";" memberparam) /
                (";" roleparam) / (";" partstatparam) /
                (";" rsvpparam) / (";" deltoparam) /
                (";" delfromparam) / (";" sentbyparam) /
                (";" cnparam) / (";" dirparam) /
                (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following are examples of this property's use for a
    to-do:
     ATTENDEE;MEMBER="mailto:DEV-GROUP@example.com":
      mailto:joecool@example.com
     ATTENDEE;DELEGATED-FROM="mailto:immud@example.com":
      mailto:ildoit@example.com

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    The following is an example of this property used for specifying
    multiple attendees to an event:
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;CN=Henry
      Cabot:mailto:hcabot@example.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;DELEGATED-FROM="mailto:bob@
      example.com";PARTSTAT=ACCEPTED;CN=Jane Doe:mailto:jdoe@
      example.com
    The following is an example of this property with a URI to the
    directory information associated with the attendee:
     ATTENDEE;CN=John Smith;DIR="ldap://example.com:6666/o=ABC%
      20Industries,c=US???(cn=Jim%20Dolittle)":mailto:jimdo@
      example.com
    The following is an example of this property with "delegatee" and
    "delegator" information for an event:
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;DELEGATED-FROM=
      "mailto:iamboss@example.com";CN=Henry Cabot:mailto:hcabot@
      example.com
     ATTENDEE;ROLE=NON-PARTICIPANT;PARTSTAT=DELEGATED;DELEGATED-TO=
      "mailto:hcabot@example.com";CN=The Big Cheese:mailto:iamboss
      @example.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;CN=Jane Doe
      :mailto:jdoe@example.com
 Example:  The following is an example of this property's use when
    another calendar user is acting on behalf of the "Attendee":
     ATTENDEE;SENT-BY=mailto:jan_doe@example.com;CN=John Smith:
      mailto:jsmith@example.com

3.8.4.2. Contact

 Property Name:  CONTACT
 Purpose:  This property is used to represent contact information or
    alternately a reference to contact information associated with the
    calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, alternate text
    representation, and language property parameters can be specified
    on this property.

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 Conformance:  This property can be specified in a "VEVENT", "VTODO",
    "VJOURNAL", or "VFREEBUSY" calendar component.
 Description:  The property value consists of textual contact
    information.  An alternative representation for the property value
    can also be specified that refers to a URI pointing to an
    alternate form, such as a vCard [RFC2426], for the contact
    information.
 Format Definition:  This property is defined by the following
    notation:
     contact    = "CONTACT" contparam ":" text CRLF
     contparam  = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" altrepparam) / (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following is an example of this property referencing
    textual contact information:
     CONTACT:Jim Dolittle\, ABC Industries\, +1-919-555-1234
    The following is an example of this property with an alternate
    representation of an LDAP URI to a directory entry containing the
    contact information:
     CONTACT;ALTREP="ldap://example.com:6666/o=ABC%20Industries\,
      c=US???(cn=Jim%20Dolittle)":Jim Dolittle\, ABC Industries\,
      +1-919-555-1234
    The following is an example of this property with an alternate
    representation of a MIME body part containing the contact
    information, such as a vCard [RFC2426] embedded in a text/
    directory media type [RFC2425]:
     CONTACT;ALTREP="CID:part3.msg970930T083000SILVER@example.com":
      Jim Dolittle\, ABC Industries\, +1-919-555-1234

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    The following is an example of this property referencing a network
    resource, such as a vCard [RFC2426] object containing the contact
    information:
     CONTACT;ALTREP="http://example.com/pdi/jdoe.vcf":Jim
       Dolittle\, ABC Industries\, +1-919-555-1234

3.8.4.3. Organizer

 Property Name:  ORGANIZER
 Purpose:  This property defines the organizer for a calendar
    component.
 Value Type:  CAL-ADDRESS
 Property Parameters:  IANA, non-standard, language, common name,
    directory entry reference, and sent-by property parameters can be
    specified on this property.
 Conformance:  This property MUST be specified in an iCalendar object
    that specifies a group-scheduled calendar entity.  This property
    MUST be specified in an iCalendar object that specifies the
    publication of a calendar user's busy time.  This property MUST
    NOT be specified in an iCalendar object that specifies only a time
    zone definition or that defines calendar components that are not
    group-scheduled components, but are components only on a single
    user's calendar.
 Description:  This property is specified within the "VEVENT",
    "VTODO", and "VJOURNAL" calendar components to specify the
    organizer of a group-scheduled calendar entity.  The property is
    specified within the "VFREEBUSY" calendar component to specify the
    calendar user requesting the free or busy time.  When publishing a
    "VFREEBUSY" calendar component, the property is used to specify
    the calendar that the published busy time came from.
    The property has the property parameters "CN", for specifying the
    common or display name associated with the "Organizer", "DIR", for
    specifying a pointer to the directory information associated with
    the "Organizer", "SENT-BY", for specifying another calendar user
    that is acting on behalf of the "Organizer".  The non-standard
    parameters may also be specified on this property.  If the
    "LANGUAGE" property parameter is specified, the identified
    language applies to the "CN" parameter value.

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 Format Definition:  This property is defined by the following
    notation:
     organizer  = "ORGANIZER" orgparam ":"
                  cal-address CRLF
     orgparam   = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" cnparam) / (";" dirparam) / (";" sentbyparam) /
                (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
 Example:  The following is an example of this property:
     ORGANIZER;CN=John Smith:mailto:jsmith@example.com
    The following is an example of this property with a pointer to the
    directory information associated with the organizer:
     ORGANIZER;CN=JohnSmith;DIR="ldap://example.com:6666/o=DC%20Ass
      ociates,c=US???(cn=John%20Smith)":mailto:jsmith@example.com
    The following is an example of this property used by another
    calendar user who is acting on behalf of the organizer, with
    responses intended to be sent back to the organizer, not the other
    calendar user:
     ORGANIZER;SENT-BY="mailto:jane_doe@example.com":
      mailto:jsmith@example.com

3.8.4.4. Recurrence ID

 Property Name:  RECURRENCE-ID
 Purpose:  This property is used in conjunction with the "UID" and
    "SEQUENCE" properties to identify a specific instance of a
    recurring "VEVENT", "VTODO", or "VJOURNAL" calendar component.
    The property value is the original value of the "DTSTART" property
    of the recurrence instance.

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 Value Type:  The default value type is DATE-TIME.  The value type can
    be set to a DATE value type.  This property MUST have the same
    value type as the "DTSTART" property contained within the
    recurring component.  Furthermore, this property MUST be specified
    as a date with local time if and only if the "DTSTART" property
    contained within the recurring component is specified as a date
    with local time.
 Property Parameters:  IANA, non-standard, value data type, time zone
    identifier, and recurrence identifier range parameters can be
    specified on this property.
 Conformance:  This property can be specified in an iCalendar object
    containing a recurring calendar component.
 Description:  The full range of calendar components specified by a
    recurrence set is referenced by referring to just the "UID"
    property value corresponding to the calendar component.  The
    "RECURRENCE-ID" property allows the reference to an individual
    instance within the recurrence set.
    If the value of the "DTSTART" property is a DATE type value, then
    the value MUST be the calendar date for the recurrence instance.
    The DATE-TIME value is set to the time when the original
    recurrence instance would occur; meaning that if the intent is to
    change a Friday meeting to Thursday, the DATE-TIME is still set to
    the original Friday meeting.
    The "RECURRENCE-ID" property is used in conjunction with the "UID"
    and "SEQUENCE" properties to identify a particular instance of a
    recurring event, to-do, or journal.  For a given pair of "UID" and
    "SEQUENCE" property values, the "RECURRENCE-ID" value for a
    recurrence instance is fixed.
    The "RANGE" parameter is used to specify the effective range of
    recurrence instances from the instance specified by the
    "RECURRENCE-ID" property value.  The value for the range parameter
    can only be "THISANDFUTURE" to indicate a range defined by the
    given recurrence instance and all subsequent instances.
    Subsequent instances are determined by their "RECURRENCE-ID" value
    and not their current scheduled start time.  Subsequent instances
    defined in separate components are not impacted by the given
    recurrence instance.  When the given recurrence instance is
    rescheduled, all subsequent instances are also rescheduled by the
    same time difference.  For instance, if the given recurrence
    instance is rescheduled to start 2 hours later, then all
    subsequent instances are also rescheduled 2 hours later.

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    Similarly, if the duration of the given recurrence instance is
    modified, then all subsequence instances are also modified to have
    this same duration.
       Note: The "RANGE" parameter may not be appropriate to
       reschedule specific subsequent instances of complex recurring
       calendar component.  Assuming an unbounded recurring calendar
       component scheduled to occur on Mondays and Wednesdays, the
       "RANGE" parameter could not be used to reschedule only the
       future Monday instances to occur on Tuesday instead.  In such
       cases, the calendar application could simply truncate the
       unbounded recurring calendar component (i.e., with the "COUNT"
       or "UNTIL" rule parts), and create two new unbounded recurring
       calendar components for the future instances.
 Format Definition:  This property is defined by the following
    notation:
     recurid    = "RECURRENCE-ID" ridparam ":" ridval CRLF
     ridparam   = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                (";" tzidparam) / (";" rangeparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     ridval     = date-time / date
     ;Value MUST match value type
 Example:  The following are examples of this property:
     RECURRENCE-ID;VALUE=DATE:19960401
     RECURRENCE-ID;RANGE=THISANDFUTURE:19960120T120000Z

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3.8.4.5. Related To

 Property Name:  RELATED-TO
 Purpose:  This property is used to represent a relationship or
    reference between one calendar component and another.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, and relationship type
    property parameters can be specified on this property.
 Conformance:  This property can be specified in the "VEVENT",
    "VTODO", and "VJOURNAL" calendar components.
 Description:  The property value consists of the persistent, globally
    unique identifier of another calendar component.  This value would
    be represented in a calendar component by the "UID" property.
    By default, the property value points to another calendar
    component that has a PARENT relationship to the referencing
    object.  The "RELTYPE" property parameter is used to either
    explicitly state the default PARENT relationship type to the
    referenced calendar component or to override the default PARENT
    relationship type and specify either a CHILD or SIBLING
    relationship.  The PARENT relationship indicates that the calendar
    component is a subordinate of the referenced calendar component.
    The CHILD relationship indicates that the calendar component is a
    superior of the referenced calendar component.  The SIBLING
    relationship indicates that the calendar component is a peer of
    the referenced calendar component.
    Changes to a calendar component referenced by this property can
    have an implicit impact on the related calendar component.  For
    example, if a group event changes its start or end date or time,
    then the related, dependent events will need to have their start
    and end dates changed in a corresponding way.  Similarly, if a
    PARENT calendar component is cancelled or deleted, then there is
    an implied impact to the related CHILD calendar components.  This
    property is intended only to provide information on the
    relationship of calendar components.  It is up to the target
    calendar system to maintain any property implications of this
    relationship.

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 Format Definition:  This property is defined by the following
    notation:
     related    = "RELATED-TO" relparam ":" text CRLF
     relparam   = *(
                ;
                ; The following is OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" reltypeparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
    The following is an example of this property:
     RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com
     RELATED-TO:19960401-080045-4000F192713-0052@example.com

3.8.4.6. Uniform Resource Locator

 Property Name:  URL
 Purpose:  This property defines a Uniform Resource Locator (URL)
    associated with the iCalendar object.
 Value Type:  URI
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified once in the "VEVENT",
    "VTODO", "VJOURNAL", or "VFREEBUSY" calendar components.
 Description:  This property may be used in a calendar component to
    convey a location where a more dynamic rendition of the calendar
    information associated with the calendar component can be found.
    This memo does not attempt to standardize the form of the URI, nor
    the format of the resource pointed to by the property value.  If
    the URL property and Content-Location MIME header are both
    specified, they MUST point to the same resource.

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 Format Definition:  This property is defined by the following
    notation:
     url        = "URL" urlparam ":" uri CRLF
     urlparam   = *(";" other-param)
 Example:  The following is an example of this property:
     URL:http://example.com/pub/calendars/jsmith/mytime.ics

3.8.4.7. Unique Identifier

 Property Name:  UID
 Purpose:  This property defines the persistent, globally unique
    identifier for the calendar component.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  The property MUST be specified in the "VEVENT",
    "VTODO", "VJOURNAL", or "VFREEBUSY" calendar components.
 Description:  The "UID" itself MUST be a globally unique identifier.
    The generator of the identifier MUST guarantee that the identifier
    is unique.  There are several algorithms that can be used to
    accomplish this.  A good method to assure uniqueness is to put the
    domain name or a domain literal IP address of the host on which
    the identifier was created on the right-hand side of an "@", and
    on the left-hand side, put a combination of the current calendar
    date and time of day (i.e., formatted in as a DATE-TIME value)
    along with some other currently unique (perhaps sequential)
    identifier available on the system (for example, a process id
    number).  Using a DATE-TIME value on the left-hand side and a
    domain name or domain literal on the right-hand side makes it
    possible to guarantee uniqueness since no two hosts should be
    using the same domain name or IP address at the same time.  Though
    other algorithms will work, it is RECOMMENDED that the right-hand
    side contain some domain identifier (either of the host itself or
    otherwise) such that the generator of the message identifier can
    guarantee the uniqueness of the left-hand side within the scope of
    that domain.
    This is the method for correlating scheduling messages with the
    referenced "VEVENT", "VTODO", or "VJOURNAL" calendar component.

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    The full range of calendar components specified by a recurrence
    set is referenced by referring to just the "UID" property value
    corresponding to the calendar component.  The "RECURRENCE-ID"
    property allows the reference to an individual instance within the
    recurrence set.
    This property is an important method for group-scheduling
    applications to match requests with later replies, modifications,
    or deletion requests.  Calendaring and scheduling applications
    MUST generate this property in "VEVENT", "VTODO", and "VJOURNAL"
    calendar components to assure interoperability with other group-
    scheduling applications.  This identifier is created by the
    calendar system that generates an iCalendar object.
    Implementations MUST be able to receive and persist values of at
    least 255 octets for this property, but they MUST NOT truncate
    values in the middle of a UTF-8 multi-octet sequence.
 Format Definition:  This property is defined by the following
    notation:
     uid        = "UID" uidparam ":" text CRLF
     uidparam   = *(";" other-param)
 Example:  The following is an example of this property:
     UID:19960401T080045Z-4000F192713-0052@example.com

3.8.5. Recurrence Component Properties

 The following properties specify recurrence information in calendar
 components.

3.8.5.1. Exception Date-Times

 Property Name:  EXDATE
 Purpose:  This property defines the list of DATE-TIME exceptions for
    recurring events, to-dos, journal entries, or time zone
    definitions.
 Value Type:  The default value type for this property is DATE-TIME.
    The value type can be set to DATE.
 Property Parameters:  IANA, non-standard, value data type, and time
    zone identifier property parameters can be specified on this
    property.

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 Conformance:  This property can be specified in recurring "VEVENT",
    "VTODO", and "VJOURNAL" calendar components as well as in the
    "STANDARD" and "DAYLIGHT" sub-components of the "VTIMEZONE"
    calendar component.
 Description:  The exception dates, if specified, are used in
    computing the recurrence set.  The recurrence set is the complete
    set of recurrence instances for a calendar component.  The
    recurrence set is generated by considering the initial "DTSTART"
    property along with the "RRULE", "RDATE", and "EXDATE" properties
    contained within the recurring component.  The "DTSTART" property
    defines the first instance in the recurrence set.  The "DTSTART"
    property value SHOULD match the pattern of the recurrence rule, if
    specified.  The recurrence set generated with a "DTSTART" property
    value that doesn't match the pattern of the rule is undefined.
    The final recurrence set is generated by gathering all of the
    start DATE-TIME values generated by any of the specified "RRULE"
    and "RDATE" properties, and then excluding any start DATE-TIME
    values specified by "EXDATE" properties.  This implies that start
    DATE-TIME values specified by "EXDATE" properties take precedence
    over those specified by inclusion properties (i.e., "RDATE" and
    "RRULE").  When duplicate instances are generated by the "RRULE"
    and "RDATE" properties, only one recurrence is considered.
    Duplicate instances are ignored.
    The "EXDATE" property can be used to exclude the value specified
    in "DTSTART".  However, in such cases, the original "DTSTART" date
    MUST still be maintained by the calendaring and scheduling system
    because the original "DTSTART" value has inherent usage
    dependencies by other properties such as the "RECURRENCE-ID".
 Format Definition:  This property is defined by the following
    notation:

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     exdate     = "EXDATE" exdtparam ":" exdtval *("," exdtval) CRLF
     exdtparam  = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                ;
                (";" tzidparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     exdtval    = date-time / date
     ;Value MUST match value type
 Example:  The following is an example of this property:
     EXDATE:19960402T010000Z,19960403T010000Z,19960404T010000Z

3.8.5.2. Recurrence Date-Times

 Property Name:  RDATE
 Purpose:  This property defines the list of DATE-TIME values for
    recurring events, to-dos, journal entries, or time zone
    definitions.
 Value Type:  The default value type for this property is DATE-TIME.
    The value type can be set to DATE or PERIOD.
 Property Parameters:  IANA, non-standard, value data type, and time
    zone identifier property parameters can be specified on this
    property.
 Conformance:  This property can be specified in recurring "VEVENT",
    "VTODO", and "VJOURNAL" calendar components as well as in the
    "STANDARD" and "DAYLIGHT" sub-components of the "VTIMEZONE"
    calendar component.
 Description:  This property can appear along with the "RRULE"
    property to define an aggregate set of repeating occurrences.
    When they both appear in a recurring component, the recurrence

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    instances are defined by the union of occurrences defined by both
    the "RDATE" and "RRULE".
    The recurrence dates, if specified, are used in computing the
    recurrence set.  The recurrence set is the complete set of
    recurrence instances for a calendar component.  The recurrence set
    is generated by considering the initial "DTSTART" property along
    with the "RRULE", "RDATE", and "EXDATE" properties contained
    within the recurring component.  The "DTSTART" property defines
    the first instance in the recurrence set.  The "DTSTART" property
    value SHOULD match the pattern of the recurrence rule, if
    specified.  The recurrence set generated with a "DTSTART" property
    value that doesn't match the pattern of the rule is undefined.
    The final recurrence set is generated by gathering all of the
    start DATE-TIME values generated by any of the specified "RRULE"
    and "RDATE" properties, and then excluding any start DATE-TIME
    values specified by "EXDATE" properties.  This implies that start
    DATE-TIME values specified by "EXDATE" properties take precedence
    over those specified by inclusion properties (i.e., "RDATE" and
    "RRULE").  Where duplicate instances are generated by the "RRULE"
    and "RDATE" properties, only one recurrence is considered.
    Duplicate instances are ignored.
 Format Definition:  This property is defined by the following
    notation:
     rdate      = "RDATE" rdtparam ":" rdtval *("," rdtval) CRLF
     rdtparam   = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" ("DATE-TIME" / "DATE" / "PERIOD")) /
                (";" tzidparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     rdtval     = date-time / date / period
     ;Value MUST match value type

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 Example:  The following are examples of this property:
     RDATE:19970714T123000Z
     RDATE;TZID=America/New_York:19970714T083000
     RDATE;VALUE=PERIOD:19960403T020000Z/19960403T040000Z,
      19960404T010000Z/PT3H
     RDATE;VALUE=DATE:19970101,19970120,19970217,19970421
      19970526,19970704,19970901,19971014,19971128,19971129,19971225

3.8.5.3. Recurrence Rule

 Property Name:  RRULE
 Purpose:  This property defines a rule or repeating pattern for
    recurring events, to-dos, journal entries, or time zone
    definitions.
 Value Type:  RECUR
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in recurring "VEVENT",
    "VTODO", and "VJOURNAL" calendar components as well as in the
    "STANDARD" and "DAYLIGHT" sub-components of the "VTIMEZONE"
    calendar component, but it SHOULD NOT be specified more than once.
    The recurrence set generated with multiple "RRULE" properties is
    undefined.
 Description:  The recurrence rule, if specified, is used in computing
    the recurrence set.  The recurrence set is the complete set of
    recurrence instances for a calendar component.  The recurrence set
    is generated by considering the initial "DTSTART" property along
    with the "RRULE", "RDATE", and "EXDATE" properties contained
    within the recurring component.  The "DTSTART" property defines
    the first instance in the recurrence set.  The "DTSTART" property
    value SHOULD be synchronized with the recurrence rule, if
    specified.  The recurrence set generated with a "DTSTART" property
    value not synchronized with the recurrence rule is undefined.  The
    final recurrence set is generated by gathering all of the start
    DATE-TIME values generated by any of the specified "RRULE" and
    "RDATE" properties, and then excluding any start DATE-TIME values
    specified by "EXDATE" properties.  This implies that start DATE-
    TIME values specified by "EXDATE" properties take precedence over
    those specified by inclusion properties (i.e., "RDATE" and
    "RRULE").  Where duplicate instances are generated by the "RRULE"

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    and "RDATE" properties, only one recurrence is considered.
    Duplicate instances are ignored.
    The "DTSTART" property specified within the iCalendar object
    defines the first instance of the recurrence.  In most cases, a
    "DTSTART" property of DATE-TIME value type used with a recurrence
    rule, should be specified as a date with local time and time zone
    reference to make sure all the recurrence instances start at the
    same local time regardless of time zone changes.
    If the duration of the recurring component is specified with the
    "DTEND" or "DUE" property, then the same exact duration will apply
    to all the members of the generated recurrence set.  Else, if the
    duration of the recurring component is specified with the
    "DURATION" property, then the same nominal duration will apply to
    all the members of the generated recurrence set and the exact
    duration of each recurrence instance will depend on its specific
    start time.  For example, recurrence instances of a nominal
    duration of one day will have an exact duration of more or less
    than 24 hours on a day where a time zone shift occurs.  The
    duration of a specific recurrence may be modified in an exception
    component or simply by using an "RDATE" property of PERIOD value
    type.
 Format Definition:  This property is defined by the following
    notation:
     rrule      = "RRULE" rrulparam ":" recur CRLF
     rrulparam  = *(";" other-param)
 Example:  All examples assume the Eastern United States time zone.
    Daily for 10 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=DAILY;COUNT=10
     ==> (1997 9:00 AM EDT) September 2-11
    Daily until December 24, 1997:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=DAILY;UNTIL=19971224T000000Z
     ==> (1997 9:00 AM EDT) September 2-30;October 1-25
         (1997 9:00 AM EST) October 26-31;November 1-30;December 1-23

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    Every other day - forever:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=DAILY;INTERVAL=2
     ==> (1997 9:00 AM EDT) September 2,4,6,8...24,26,28,30;
                            October 2,4,6...20,22,24
         (1997 9:00 AM EST) October 26,28,30;
                            November 1,3,5,7...25,27,29;
                            December 1,3,...
    Every 10 days, 5 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=DAILY;INTERVAL=10;COUNT=5
     ==> (1997 9:00 AM EDT) September 2,12,22;
                            October 2,12
    Every day in January, for 3 years:
     DTSTART;TZID=America/New_York:19980101T090000
     RRULE:FREQ=YEARLY;UNTIL=20000131T140000Z;
      BYMONTH=1;BYDAY=SU,MO,TU,WE,TH,FR,SA
     or
     RRULE:FREQ=DAILY;UNTIL=20000131T140000Z;BYMONTH=1
     ==> (1998 9:00 AM EST)January 1-31
         (1999 9:00 AM EST)January 1-31
         (2000 9:00 AM EST)January 1-31
    Weekly for 10 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=WEEKLY;COUNT=10
     ==> (1997 9:00 AM EDT) September 2,9,16,23,30;October 7,14,21
         (1997 9:00 AM EST) October 28;November 4

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    Weekly until December 24, 1997:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=WEEKLY;UNTIL=19971224T000000Z
     ==> (1997 9:00 AM EDT) September 2,9,16,23,30;
                            October 7,14,21
         (1997 9:00 AM EST) October 28;
                            November 4,11,18,25;
                            December 2,9,16,23
    Every other week - forever:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;WKST=SU
     ==> (1997 9:00 AM EDT) September 2,16,30;
                            October 14
         (1997 9:00 AM EST) October 28;
                            November 11,25;
                            December 9,23
         (1998 9:00 AM EST) January 6,20;
                            February 3, 17
         ...
    Weekly on Tuesday and Thursday for five weeks:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=WEEKLY;UNTIL=19971007T000000Z;WKST=SU;BYDAY=TU,TH
     or
     RRULE:FREQ=WEEKLY;COUNT=10;WKST=SU;BYDAY=TU,TH
     ==> (1997 9:00 AM EDT) September 2,4,9,11,16,18,23,25,30;
                            October 2
    Every other week on Monday, Wednesday, and Friday until December
    24, 1997, starting on Monday, September 1, 1997:
     DTSTART;TZID=America/New_York:19970901T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;UNTIL=19971224T000000Z;WKST=SU;
      BYDAY=MO,WE,FR
     ==> (1997 9:00 AM EDT) September 1,3,5,15,17,19,29;
                            October 1,3,13,15,17
         (1997 9:00 AM EST) October 27,29,31;
                            November 10,12,14,24,26,28;

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                            December 8,10,12,22
    Every other week on Tuesday and Thursday, for 8 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH
     ==> (1997 9:00 AM EDT) September 2,4,16,18,30;
                            October 2,14,16
    Monthly on the first Friday for 10 occurrences:
     DTSTART;TZID=America/New_York:19970905T090000
     RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR
     ==> (1997 9:00 AM EDT) September 5;October 3
         (1997 9:00 AM EST) November 7;December 5
         (1998 9:00 AM EST) January 2;February 6;March 6;April 3
         (1998 9:00 AM EDT) May 1;June 5
    Monthly on the first Friday until December 24, 1997:
     DTSTART;TZID=America/New_York:19970905T090000
     RRULE:FREQ=MONTHLY;UNTIL=19971224T000000Z;BYDAY=1FR
     ==> (1997 9:00 AM EDT) September 5; October 3
         (1997 9:00 AM EST) November 7; December 5
    Every other month on the first and last Sunday of the month for 10
    occurrences:
     DTSTART;TZID=America/New_York:19970907T090000
     RRULE:FREQ=MONTHLY;INTERVAL=2;COUNT=10;BYDAY=1SU,-1SU
     ==> (1997 9:00 AM EDT) September 7,28
         (1997 9:00 AM EST) November 2,30
         (1998 9:00 AM EST) January 4,25;March 1,29
         (1998 9:00 AM EDT) May 3,31
    Monthly on the second-to-last Monday of the month for 6 months:
     DTSTART;TZID=America/New_York:19970922T090000
     RRULE:FREQ=MONTHLY;COUNT=6;BYDAY=-2MO
     ==> (1997 9:00 AM EDT) September 22;October 20
         (1997 9:00 AM EST) November 17;December 22
         (1998 9:00 AM EST) January 19;February 16

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    Monthly on the third-to-the-last day of the month, forever:
     DTSTART;TZID=America/New_York:19970928T090000
     RRULE:FREQ=MONTHLY;BYMONTHDAY=-3
     ==> (1997 9:00 AM EDT) September 28
         (1997 9:00 AM EST) October 29;November 28;December 29
         (1998 9:00 AM EST) January 29;February 26
         ...
    Monthly on the 2nd and 15th of the month for 10 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=2,15
     ==> (1997 9:00 AM EDT) September 2,15;October 2,15
         (1997 9:00 AM EST) November 2,15;December 2,15
         (1998 9:00 AM EST) January 2,15
    Monthly on the first and last day of the month for 10 occurrences:
     DTSTART;TZID=America/New_York:19970930T090000
     RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=1,-1
     ==> (1997 9:00 AM EDT) September 30;October 1
         (1997 9:00 AM EST) October 31;November 1,30;December 1,31
         (1998 9:00 AM EST) January 1,31;February 1
    Every 18 months on the 10th thru 15th of the month for 10
    occurrences:
     DTSTART;TZID=America/New_York:19970910T090000
     RRULE:FREQ=MONTHLY;INTERVAL=18;COUNT=10;BYMONTHDAY=10,11,12,
      13,14,15
     ==> (1997 9:00 AM EDT) September 10,11,12,13,14,15
         (1999 9:00 AM EST) March 10,11,12,13
    Every Tuesday, every other month:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=MONTHLY;INTERVAL=2;BYDAY=TU
     ==> (1997 9:00 AM EDT) September 2,9,16,23,30
         (1997 9:00 AM EST) November 4,11,18,25
         (1998 9:00 AM EST) January 6,13,20,27;March 3,10,17,24,31
         ...

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    Yearly in June and July for 10 occurrences:
     DTSTART;TZID=America/New_York:19970610T090000
     RRULE:FREQ=YEARLY;COUNT=10;BYMONTH=6,7
     ==> (1997 9:00 AM EDT) June 10;July 10
         (1998 9:00 AM EDT) June 10;July 10
         (1999 9:00 AM EDT) June 10;July 10
         (2000 9:00 AM EDT) June 10;July 10
         (2001 9:00 AM EDT) June 10;July 10
       Note: Since none of the BYDAY, BYMONTHDAY, or BYYEARDAY
       components are specified, the day is gotten from "DTSTART".
    Every other year on January, February, and March for 10
    occurrences:
     DTSTART;TZID=America/New_York:19970310T090000
     RRULE:FREQ=YEARLY;INTERVAL=2;COUNT=10;BYMONTH=1,2,3
     ==> (1997 9:00 AM EST) March 10
         (1999 9:00 AM EST) January 10;February 10;March 10
         (2001 9:00 AM EST) January 10;February 10;March 10
         (2003 9:00 AM EST) January 10;February 10;March 10
    Every third year on the 1st, 100th, and 200th day for 10
    occurrences:
     DTSTART;TZID=America/New_York:19970101T090000
     RRULE:FREQ=YEARLY;INTERVAL=3;COUNT=10;BYYEARDAY=1,100,200
     ==> (1997 9:00 AM EST) January 1
         (1997 9:00 AM EDT) April 10;July 19
         (2000 9:00 AM EST) January 1
         (2000 9:00 AM EDT) April 9;July 18
         (2003 9:00 AM EST) January 1
         (2003 9:00 AM EDT) April 10;July 19
         (2006 9:00 AM EST) January 1
    Every 20th Monday of the year, forever:
     DTSTART;TZID=America/New_York:19970519T090000
     RRULE:FREQ=YEARLY;BYDAY=20MO
     ==> (1997 9:00 AM EDT) May 19
         (1998 9:00 AM EDT) May 18
         (1999 9:00 AM EDT) May 17
         ...

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    Monday of week number 20 (where the default start of the week is
    Monday), forever:
     DTSTART;TZID=America/New_York:19970512T090000
     RRULE:FREQ=YEARLY;BYWEEKNO=20;BYDAY=MO
     ==> (1997 9:00 AM EDT) May 12
         (1998 9:00 AM EDT) May 11
         (1999 9:00 AM EDT) May 17
         ...
    Every Thursday in March, forever:
     DTSTART;TZID=America/New_York:19970313T090000
     RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=TH
     ==> (1997 9:00 AM EST) March 13,20,27
         (1998 9:00 AM EST) March 5,12,19,26
         (1999 9:00 AM EST) March 4,11,18,25
         ...
    Every Thursday, but only during June, July, and August, forever:
     DTSTART;TZID=America/New_York:19970605T090000
     RRULE:FREQ=YEARLY;BYDAY=TH;BYMONTH=6,7,8
     ==> (1997 9:00 AM EDT) June 5,12,19,26;July 3,10,17,24,31;
                            August 7,14,21,28
         (1998 9:00 AM EDT) June 4,11,18,25;July 2,9,16,23,30;
                            August 6,13,20,27
         (1999 9:00 AM EDT) June 3,10,17,24;July 1,8,15,22,29;
                            August 5,12,19,26
         ...
    Every Friday the 13th, forever:
     DTSTART;TZID=America/New_York:19970902T090000
     EXDATE;TZID=America/New_York:19970902T090000
     RRULE:FREQ=MONTHLY;BYDAY=FR;BYMONTHDAY=13
     ==> (1998 9:00 AM EST) February 13;March 13;November 13
         (1999 9:00 AM EDT) August 13
         (2000 9:00 AM EDT) October 13
         ...

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    The first Saturday that follows the first Sunday of the month,
    forever:
     DTSTART;TZID=America/New_York:19970913T090000
     RRULE:FREQ=MONTHLY;BYDAY=SA;BYMONTHDAY=7,8,9,10,11,12,13
     ==> (1997 9:00 AM EDT) September 13;October 11
         (1997 9:00 AM EST) November 8;December 13
         (1998 9:00 AM EST) January 10;February 7;March 7
         (1998 9:00 AM EDT) April 11;May 9;June 13...
         ...
    Every 4 years, the first Tuesday after a Monday in November,
    forever (U.S. Presidential Election day):
     DTSTART;TZID=America/New_York:19961105T090000
     RRULE:FREQ=YEARLY;INTERVAL=4;BYMONTH=11;BYDAY=TU;
      BYMONTHDAY=2,3,4,5,6,7,8
      ==> (1996 9:00 AM EST) November 5
          (2000 9:00 AM EST) November 7
          (2004 9:00 AM EST) November 2
          ...
    The third instance into the month of one of Tuesday, Wednesday, or
    Thursday, for the next 3 months:
     DTSTART;TZID=America/New_York:19970904T090000
     RRULE:FREQ=MONTHLY;COUNT=3;BYDAY=TU,WE,TH;BYSETPOS=3
     ==> (1997 9:00 AM EDT) September 4;October 7
         (1997 9:00 AM EST) November 6
    The second-to-last weekday of the month:
     DTSTART;TZID=America/New_York:19970929T090000
     RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-2
     ==> (1997 9:00 AM EDT) September 29
         (1997 9:00 AM EST) October 30;November 27;December 30
         (1998 9:00 AM EST) January 29;February 26;March 30
         ...

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    Every 3 hours from 9:00 AM to 5:00 PM on a specific day:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=HOURLY;INTERVAL=3;UNTIL=19970902T170000Z
     ==> (September 2, 1997 EDT) 09:00,12:00,15:00
    Every 15 minutes for 6 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=MINUTELY;INTERVAL=15;COUNT=6
     ==> (September 2, 1997 EDT) 09:00,09:15,09:30,09:45,10:00,10:15
    Every hour and a half for 4 occurrences:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=MINUTELY;INTERVAL=90;COUNT=4
     ==> (September 2, 1997 EDT) 09:00,10:30;12:00;13:30
    Every 20 minutes from 9:00 AM to 4:40 PM every day:
     DTSTART;TZID=America/New_York:19970902T090000
     RRULE:FREQ=DAILY;BYHOUR=9,10,11,12,13,14,15,16;BYMINUTE=0,20,40
     or
     RRULE:FREQ=MINUTELY;INTERVAL=20;BYHOUR=9,10,11,12,13,14,15,16
     ==> (September 2, 1997 EDT) 9:00,9:20,9:40,10:00,10:20,
                                 ... 16:00,16:20,16:40
         (September 3, 1997 EDT) 9:00,9:20,9:40,10:00,10:20,
                                 ...16:00,16:20,16:40
         ...
    An example where the days generated makes a difference because of
    WKST:
     DTSTART;TZID=America/New_York:19970805T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=MO
     ==> (1997 EDT) August 5,10,19,24
    changing only WKST from MO to SU, yields different results...
     DTSTART;TZID=America/New_York:19970805T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=SU
     ==> (1997 EDT) August 5,17,19,31

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    An example where an invalid date (i.e., February 30) is ignored.
     DTSTART;TZID=America/New_York:20070115T090000
     RRULE:FREQ=MONTHLY;BYMONTHDAY=15,30;COUNT=5
     ==> (2007 EST) January 15,30
         (2007 EST) February 15
         (2007 EDT) March 15,30

3.8.6. Alarm Component Properties

 The following properties specify alarm information in calendar
 components.

3.8.6.1. Action

 Property Name:  ACTION
 Purpose:  This property defines the action to be invoked when an
    alarm is triggered.
 Value Type:  TEXT
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property MUST be specified once in a "VALARM"
    calendar component.
 Description:  Each "VALARM" calendar component has a particular type
    of action with which it is associated.  This property specifies
    the type of action.  Applications MUST ignore alarms with x-name
    and iana-token values they don't recognize.
 Format Definition:  This property is defined by the following
    notation:
     action      = "ACTION" actionparam ":" actionvalue CRLF
     actionparam = *(";" other-param)
     actionvalue = "AUDIO" / "DISPLAY" / "EMAIL"
                 / iana-token / x-name
 Example:  The following are examples of this property in a "VALARM"
    calendar component:

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     ACTION:AUDIO
     ACTION:DISPLAY

3.8.6.2. Repeat Count

 Property Name:  REPEAT
 Purpose:  This property defines the number of times the alarm should
    be repeated, after the initial trigger.
 Value Type:  INTEGER
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in a "VALARM" calendar
    component.
 Description:  This property defines the number of times an alarm
    should be repeated after its initial trigger.  If the alarm
    triggers more than once, then this property MUST be specified
    along with the "DURATION" property.
 Format Definition:  This property is defined by the following
    notation:
     repeat  = "REPEAT" repparam ":" integer CRLF
     ;Default is "0", zero.
     repparam   = *(";" other-param)
 Example:  The following is an example of this property for an alarm
    that repeats 4 additional times with a 5-minute delay after the
    initial triggering of the alarm:
     REPEAT:4
     DURATION:PT5M

3.8.6.3. Trigger

 Property Name:  TRIGGER
 Purpose:  This property specifies when an alarm will trigger.
 Value Type:  The default value type is DURATION.  The value type can
    be set to a DATE-TIME value type, in which case the value MUST
    specify a UTC-formatted DATE-TIME value.

Desruisseaux Standards Track [Page 133] RFC 5545 iCalendar September 2009

 Property Parameters:  IANA, non-standard, value data type, time zone
    identifier, or trigger relationship property parameters can be
    specified on this property.  The trigger relationship property
    parameter MUST only be specified when the value type is
    "DURATION".
 Conformance:  This property MUST be specified in the "VALARM"
    calendar component.
 Description:  This property defines when an alarm will trigger.  The
    default value type is DURATION, specifying a relative time for the
    trigger of the alarm.  The default duration is relative to the
    start of an event or to-do with which the alarm is associated.
    The duration can be explicitly set to trigger from either the end
    or the start of the associated event or to-do with the "RELATED"
    parameter.  A value of START will set the alarm to trigger off the
    start of the associated event or to-do.  A value of END will set
    the alarm to trigger off the end of the associated event or to-do.
    Either a positive or negative duration may be specified for the
    "TRIGGER" property.  An alarm with a positive duration is
    triggered after the associated start or end of the event or to-do.
    An alarm with a negative duration is triggered before the
    associated start or end of the event or to-do.
    The "RELATED" property parameter is not valid if the value type of
    the property is set to DATE-TIME (i.e., for an absolute date and
    time alarm trigger).  If a value type of DATE-TIME is specified,
    then the property value MUST be specified in the UTC time format.
    If an absolute trigger is specified on an alarm for a recurring
    event or to-do, then the alarm will only trigger for the specified
    absolute DATE-TIME, along with any specified repeating instances.
    If the trigger is set relative to START, then the "DTSTART"
    property MUST be present in the associated "VEVENT" or "VTODO"
    calendar component.  If an alarm is specified for an event with
    the trigger set relative to the END, then the "DTEND" property or
    the "DTSTART" and "DURATION " properties MUST be present in the
    associated "VEVENT" calendar component.  If the alarm is specified
    for a to-do with a trigger set relative to the END, then either
    the "DUE" property or the "DTSTART" and "DURATION " properties
    MUST be present in the associated "VTODO" calendar component.
    Alarms specified in an event or to-do that is defined in terms of
    a DATE value type will be triggered relative to 00:00:00 of the
    user's configured time zone on the specified date, or relative to
    00:00:00 UTC on the specified date if no configured time zone can
    be found for the user.  For example, if "DTSTART" is a DATE value

Desruisseaux Standards Track [Page 134] RFC 5545 iCalendar September 2009

    set to 19980205 then the duration trigger will be relative to
    19980205T000000 America/New_York for a user configured with the
    America/New_York time zone.
 Format Definition:  This property is defined by the following
    notation:
     trigger    = "TRIGGER" (trigrel / trigabs) CRLF
     trigrel    = *(
                ;
                ; The following are OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" "DURATION") /
                (";" trigrelparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                ) ":"  dur-value
     trigabs    = *(
                ;
                ; The following is REQUIRED,
                ; but MUST NOT occur more than once.
                ;
                (";" "VALUE" "=" "DATE-TIME") /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                ) ":" date-time
 Example:  A trigger set 15 minutes prior to the start of the event or
    to-do.
     TRIGGER:-PT15M
    A trigger set five minutes after the end of an event or the due
    date of a to-do.
     TRIGGER;RELATED=END:PT5M

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    A trigger set to an absolute DATE-TIME.
     TRIGGER;VALUE=DATE-TIME:19980101T050000Z

3.8.7. Change Management Component Properties

 The following properties specify change management information in
 calendar components.

3.8.7.1. Date-Time Created

 Property Name:  CREATED
 Purpose:  This property specifies the date and time that the calendar
    information was created by the calendar user agent in the calendar
    store.
       Note: This is analogous to the creation date and time for a
       file in the file system.
 Value Type:  DATE-TIME
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  The property can be specified once in "VEVENT",
    "VTODO", or "VJOURNAL" calendar components.  The value MUST be
    specified as a date with UTC time.
 Description:  This property specifies the date and time that the
    calendar information was created by the calendar user agent in the
    calendar store.
 Format Definition:  This property is defined by the following
    notation:
     created    = "CREATED" creaparam ":" date-time CRLF
     creaparam  = *(";" other-param)
 Example:  The following is an example of this property:
     CREATED:19960329T133000Z

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3.8.7.2. Date-Time Stamp

 Property Name:  DTSTAMP
 Purpose:  In the case of an iCalendar object that specifies a
    "METHOD" property, this property specifies the date and time that
    the instance of the iCalendar object was created.  In the case of
    an iCalendar object that doesn't specify a "METHOD" property, this
    property specifies the date and time that the information
    associated with the calendar component was last revised in the
    calendar store.
 Value Type:  DATE-TIME
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property MUST be included in the "VEVENT",
    "VTODO", "VJOURNAL", or "VFREEBUSY" calendar components.
 Description:  The value MUST be specified in the UTC time format.
    This property is also useful to protocols such as [2447bis] that
    have inherent latency issues with the delivery of content.  This
    property will assist in the proper sequencing of messages
    containing iCalendar objects.
    In the case of an iCalendar object that specifies a "METHOD"
    property, this property differs from the "CREATED" and "LAST-
    MODIFIED" properties.  These two properties are used to specify
    when the particular calendar data in the calendar store was
    created and last modified.  This is different than when the
    iCalendar object representation of the calendar service
    information was created or last modified.
    In the case of an iCalendar object that doesn't specify a "METHOD"
    property, this property is equivalent to the "LAST-MODIFIED"
    property.
 Format Definition:  This property is defined by the following
    notation:
     dtstamp    = "DTSTAMP" stmparam ":" date-time CRLF
     stmparam   = *(";" other-param)

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 Example:
     DTSTAMP:19971210T080000Z

3.8.7.3. Last Modified

 Property Name:  LAST-MODIFIED
 Purpose:  This property specifies the date and time that the
    information associated with the calendar component was last
    revised in the calendar store.
       Note: This is analogous to the modification date and time for a
       file in the file system.
 Value Type:  DATE-TIME
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.
 Conformance:  This property can be specified in the "VEVENT",
    "VTODO", "VJOURNAL", or "VTIMEZONE" calendar components.
 Description:  The property value MUST be specified in the UTC time
    format.
 Format Definition:  This property is defined by the following
    notation:
     last-mod   = "LAST-MODIFIED" lstparam ":" date-time CRLF
     lstparam   = *(";" other-param)
 Example:  The following is an example of this property:
     LAST-MODIFIED:19960817T133000Z

3.8.7.4. Sequence Number

 Property Name:  SEQUENCE
 Purpose:  This property defines the revision sequence number of the
    calendar component within a sequence of revisions.
 Value Type:  INTEGER
 Property Parameters:  IANA and non-standard property parameters can
    be specified on this property.

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 Conformance:  The property can be specified in "VEVENT", "VTODO", or
    "VJOURNAL" calendar component.
 Description:  When a calendar component is created, its sequence
    number is 0.  It is monotonically incremented by the "Organizer's"
    CUA each time the "Organizer" makes a significant revision to the
    calendar component.
    The "Organizer" includes this property in an iCalendar object that
    it sends to an "Attendee" to specify the current version of the
    calendar component.
    The "Attendee" includes this property in an iCalendar object that
    it sends to the "Organizer" to specify the version of the calendar
    component to which the "Attendee" is referring.
    A change to the sequence number is not the mechanism that an
    "Organizer" uses to request a response from the "Attendees".  The
    "RSVP" parameter on the "ATTENDEE" property is used by the
    "Organizer" to indicate that a response from the "Attendees" is
    requested.
    Recurrence instances of a recurring component MAY have different
    sequence numbers.
 Format Definition:  This property is defined by the following
    notation:
     seq = "SEQUENCE" seqparam ":" integer CRLF
     ; Default is "0"
     seqparam   = *(";" other-param)
 Example:  The following is an example of this property for a calendar
    component that was just created by the "Organizer":
     SEQUENCE:0
    The following is an example of this property for a calendar
    component that has been revised two different times by the
    "Organizer":
     SEQUENCE:2

3.8.8. Miscellaneous Component Properties

 The following properties specify information about a number of
 miscellaneous features of calendar components.

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3.8.8.1. IANA Properties

 Property Name:  An IANA-registered property name
 Value Type:  The default value type is TEXT.  The value type can be
    set to any value type.
 Property Parameters:  Any parameter can be specified on this
    property.
 Description:  This specification allows other properties registered
    with IANA to be specified in any calendar components.  Compliant
    applications are expected to be able to parse these other IANA-
    registered properties but can ignore them.
 Format Definition:  This property is defined by the following
    notation:
     iana-prop = iana-token *(";" icalparameter) ":" value CRLF
 Example:  The following are examples of properties that might be
    registered to IANA:
     DRESSCODE:CASUAL
     NON-SMOKING;VALUE=BOOLEAN:TRUE

3.8.8.2. Non-Standard Properties

 Property Name:  Any property name with a "X-" prefix
 Purpose:  This class of property provides a framework for defining
    non-standard properties.
 Value Type:  The default value type is TEXT.  The value type can be
    set to any value type.
 Property Parameters:  IANA, non-standard, and language property
    parameters can be specified on this property.
 Conformance:  This property can be specified in any calendar
    component.
 Description:  The MIME Calendaring and Scheduling Content Type
    provides a "standard mechanism for doing non-standard things".
    This extension support is provided for implementers to "push the
    envelope" on the existing version of the memo.  Extension
    properties are specified by property and/or property parameter

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    names that have the prefix text of "X-" (the two-character
    sequence: LATIN CAPITAL LETTER X character followed by the HYPHEN-
    MINUS character).  It is recommended that vendors concatenate onto
    this sentinel another short prefix text to identify the vendor.
    This will facilitate readability of the extensions and minimize
    possible collision of names between different vendors.  User
    agents that support this content type are expected to be able to
    parse the extension properties and property parameters but can
    ignore them.
    At present, there is no registration authority for names of
    extension properties and property parameters.  The value type for
    this property is TEXT.  Optionally, the value type can be any of
    the other valid value types.
 Format Definition:  This property is defined by the following
    notation:
     x-prop = x-name *(";" icalparameter) ":" value CRLF
 Example:  The following might be the ABC vendor's extension for an
    audio-clip form of subject property:
     X-ABC-MMSUBJ;VALUE=URI;FMTTYPE=audio/basic:http://www.example.
      org/mysubj.au

3.8.8.3. Request Status

 Property Name:  REQUEST-STATUS
 Purpose:  This property defines the status code returned for a
    scheduling request.
 Value Type:  TEXT
 Property Parameters:  IANA, non-standard, and language property
    parameters can be specified on this property.
 Conformance:  The property can be specified in the "VEVENT", "VTODO",
    "VJOURNAL", or "VFREEBUSY" calendar component.
 Description:  This property is used to return status code information
    related to the processing of an associated iCalendar object.  The
    value type for this property is TEXT.

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    The value consists of a short return status component, a longer
    return status description component, and optionally a status-
    specific data component.  The components of the value are
    separated by the SEMICOLON character.
    The short return status is a PERIOD character separated pair or
    3-tuple of integers.  For example, "3.1" or "3.1.1".  The
    successive levels of integers provide for a successive level of
    status code granularity.
    The following are initial classes for the return status code.
    Individual iCalendar object methods will define specific return
    status codes for these classes.  In addition, other classes for
    the return status code may be defined using the registration
    process defined later in this memo.
 +--------+----------------------------------------------------------+
 | Short  | Longer Return Status Description                         |
 | Return |                                                          |
 | Status |                                                          |
 | Code   |                                                          |
 +--------+----------------------------------------------------------+
 | 1.xx   | Preliminary success.  This class of status code          |
 |        | indicates that the request has been initially processed  |
 |        | but that completion is pending.                          |
 |        |                                                          |
 | 2.xx   | Successful.  This class of status code indicates that    |
 |        | the request was completed successfully.  However, the    |
 |        | exact status code can indicate that a fallback has been  |
 |        | taken.                                                   |
 |        |                                                          |
 | 3.xx   | Client Error.  This class of status code indicates that  |
 |        | the request was not successful.  The error is the result |
 |        | of either a syntax or a semantic error in the client-    |
 |        | formatted request.  Request should not be retried until  |
 |        | the condition in the request is corrected.               |
 |        |                                                          |
 | 4.xx   | Scheduling Error.  This class of status code indicates   |
 |        | that the request was not successful.  Some sort of error |
 |        | occurred within the calendaring and scheduling service,  |
 |        | not directly related to the request itself.              |
 +--------+----------------------------------------------------------+

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 Format Definition:  This property is defined by the following
    notation:
     rstatus    = "REQUEST-STATUS" rstatparam ":"
                  statcode ";" statdesc [";" extdata]
     rstatparam = *(
                ;
                ; The following is OPTIONAL,
                ; but MUST NOT occur more than once.
                ;
                (";" languageparam) /
                ;
                ; The following is OPTIONAL,
                ; and MAY occur more than once.
                ;
                (";" other-param)
                ;
                )
     statcode   = 1*DIGIT 1*2("." 1*DIGIT)
     ;Hierarchical, numeric return status code
     statdesc   = text
     ;Textual status description
     extdata    = text
     ;Textual exception data.  For example, the offending property
     ;name and value or complete property line.
 Example:  The following are some possible examples of this property.
    The COMMA and SEMICOLON separator characters in the property value
    are BACKSLASH character escaped because they appear in a text
    value.
     REQUEST-STATUS:2.0;Success
     REQUEST-STATUS:3.1;Invalid property value;DTSTART:96-Apr-01
     REQUEST-STATUS:2.8; Success\, repeating event ignored. Scheduled
      as a single event.;RRULE:FREQ=WEEKLY\;INTERVAL=2
     REQUEST-STATUS:4.1;Event conflict.  Date-time is busy.
     REQUEST-STATUS:3.7;Invalid calendar user;ATTENDEE:
      mailto:jsmith@example.com

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4. iCalendar Object Examples

 The following examples are provided as an informational source of
 illustrative iCalendar objects consistent with this content type.
 The following example specifies a three-day conference that begins at
 2:30 P.M. UTC, September 18, 1996 and ends at 10:00 P.M. UTC,
 September 20, 1996.
     BEGIN:VCALENDAR
     PRODID:-//xyz Corp//NONSGML PDA Calendar Version 1.0//EN
     VERSION:2.0
     BEGIN:VEVENT
     DTSTAMP:19960704T120000Z
     UID:uid1@example.com
     ORGANIZER:mailto:jsmith@example.com
     DTSTART:19960918T143000Z
     DTEND:19960920T220000Z
     STATUS:CONFIRMED
     CATEGORIES:CONFERENCE
     SUMMARY:Networld+Interop Conference
     DESCRIPTION:Networld+Interop Conference
       and Exhibit\nAtlanta World Congress Center\n
      Atlanta\, Georgia
     END:VEVENT
     END:VCALENDAR
 The following example specifies a group-scheduled meeting that begins
 at 8:30 AM EST on March 12, 1998 and ends at 9:30 AM EST on March 12,
 1998.  The "Organizer" has scheduled the meeting with one or more
 calendar users in a group.  A time zone specification for Eastern
 United States has been specified.
     BEGIN:VCALENDAR
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VTIMEZONE
     TZID:America/New_York
     BEGIN:STANDARD
     DTSTART:19981025T020000
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19990404T020000
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400

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     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE
     BEGIN:VEVENT
     DTSTAMP:19980309T231000Z
     UID:guid-1.example.com
     ORGANIZER:mailto:mrbig@example.com
     ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT;CUTYPE=GROUP:
      mailto:employee-A@example.com
     DESCRIPTION:Project XYZ Review Meeting
     CATEGORIES:MEETING
     CLASS:PUBLIC
     CREATED:19980309T130000Z
     SUMMARY:XYZ Project Review
     DTSTART;TZID=America/New_York:19980312T083000
     DTEND;TZID=America/New_York:19980312T093000
     LOCATION:1CP Conference Room 4350
     END:VEVENT
     END:VCALENDAR
 The following is an example of an iCalendar object passed in a MIME
 message with a single body part consisting of a "text/calendar"
 Content Type.
     TO:jsmith@example.com
     FROM:jdoe@example.com
     MIME-VERSION:1.0
     MESSAGE-ID:<id3@example.com>
     CONTENT-TYPE:text/calendar; method="xyz"; component="VEVENT"
     BEGIN:VCALENDAR
     METHOD:xyz
     VERSION:2.0
     PRODID:-//ABC Corporation//NONSGML My Product//EN
     BEGIN:VEVENT
     DTSTAMP:19970324T120000Z
     SEQUENCE:0
     UID:uid3@example.com
     ORGANIZER:mailto:jdoe@example.com
     ATTENDEE;RSVP=TRUE:mailto:jsmith@example.com
     DTSTART:19970324T123000Z
     DTEND:19970324T210000Z
     CATEGORIES:MEETING,PROJECT
     CLASS:PUBLIC
     SUMMARY:Calendaring Interoperability Planning Meeting
     DESCRIPTION:Discuss how we can test c&s interoperability\n
      using iCalendar and other IETF standards.
     LOCATION:LDB Lobby

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     ATTACH;FMTTYPE=application/postscript:ftp://example.com/pub/
      conf/bkgrnd.ps
     END:VEVENT
     END:VCALENDAR
 The following is an example of a to-do due on April 15, 1998.  An
 audio alarm has been specified to remind the calendar user at noon,
 the day before the to-do is expected to be completed and repeat
 hourly, four additional times.  The to-do definition has been
 modified twice since it was initially created.
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//ABC Corporation//NONSGML My Product//EN
     BEGIN:VTODO
     DTSTAMP:19980130T134500Z
     SEQUENCE:2
     UID:uid4@example.com
     ORGANIZER:mailto:unclesam@example.com
     ATTENDEE;PARTSTAT=ACCEPTED:mailto:jqpublic@example.com
     DUE:19980415T000000
     STATUS:NEEDS-ACTION
     SUMMARY:Submit Income Taxes
     BEGIN:VALARM
     ACTION:AUDIO
     TRIGGER:19980403T120000Z
     ATTACH;FMTTYPE=audio/basic:http://example.com/pub/audio-
      files/ssbanner.aud
     REPEAT:4
     DURATION:PT1H
     END:VALARM
     END:VTODO
     END:VCALENDAR
 The following is an example of a journal entry:
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//ABC Corporation//NONSGML My Product//EN
     BEGIN:VJOURNAL
     DTSTAMP:19970324T120000Z
     UID:uid5@example.com
     ORGANIZER:mailto:jsmith@example.com
     STATUS:DRAFT
     CLASS:PUBLIC
     CATEGORIES:Project Report,XYZ,Weekly Meeting
     DESCRIPTION:Project xyz Review Meeting Minutes\n
      Agenda\n1. Review of project version 1.0 requirements.\n2.

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       Definition
      of project processes.\n3. Review of project schedule.\n
      Participants: John Smith\, Jane Doe\, Jim Dandy\n-It was
       decided that the requirements need to be signed off by
       product marketing.\n-Project processes were accepted.\n
      -Project schedule needs to account for scheduled holidays
       and employee vacation time. Check with HR for specific
       dates.\n-New schedule will be distributed by Friday.\n-
      Next weeks meeting is cancelled. No meeting until 3/23.
     END:VJOURNAL
     END:VCALENDAR
 The following is an example of published busy time information.  The
 iCalendar object might be placed in the network resource
 http://www.example.com/calendar/busytime/jsmith.ifb.
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//RDU Software//NONSGML HandCal//EN
     BEGIN:VFREEBUSY
     ORGANIZER:mailto:jsmith@example.com
     DTSTART:19980313T141711Z
     DTEND:19980410T141711Z
     FREEBUSY:19980314T233000Z/19980315T003000Z
     FREEBUSY:19980316T153000Z/19980316T163000Z
     FREEBUSY:19980318T030000Z/19980318T040000Z
     URL:http://www.example.com/calendar/busytime/jsmith.ifb
     END:VFREEBUSY
     END:VCALENDAR

5. Recommended Practices

 These recommended practices should be followed in order to assure
 consistent handling of the following cases for an iCalendar object.
 1.  Content lines longer than 75 octets SHOULD be folded.
 2.  When the combination of the "RRULE" and "RDATE" properties in a
     recurring component produces multiple instances having the same
     start DATE-TIME value, they should be collapsed to, and
     considered as, a single instance.  If the "RDATE" property is
     specified as a PERIOD value the duration of the recurrence
     instance will be the one specified by the "RDATE" property, and
     not the duration of the recurrence instance defined by the
     "DTSTART" property.
 3.  When a calendar user receives multiple requests for the same
     calendar component (e.g., REQUEST for a "VEVENT" calendar

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     component) as a result of being on multiple mailing lists
     specified by "ATTENDEE" properties in the request, they SHOULD
     respond to only one of the requests.  The calendar user SHOULD
     also specify (using the "MEMBER" parameter of the "ATTENDEE"
     property) of which mailing list they are a member.
 4.  An implementation can truncate a "SUMMARY" property value to 255
     octets, but it MUST NOT truncate the value in the middle of a
     UTF-8 multi-octet sequence.
 5.  If seconds of the minute are not supported by an implementation,
     then a value of "00" SHOULD be specified for the seconds
     component in a time value.
 6.  "TZURL" values SHOULD NOT be specified as a file URI type.  This
     URI form can be useful within an organization, but is problematic
     in the Internet.
 7.  Some possible English values for "CATEGORIES" property include:
     "ANNIVERSARY", "APPOINTMENT", "BUSINESS", "EDUCATION", "HOLIDAY",
     "MEETING", "MISCELLANEOUS", "NON-WORKING HOURS", "NOT IN OFFICE",
     "PERSONAL", "PHONE CALL", "SICK DAY", "SPECIAL OCCASION",
     "TRAVEL", "VACATION".  Categories can be specified in any
     registered language.
 8.  Some possible English values for the "RESOURCES" property
     include: "CATERING", "CHAIRS", "COMPUTER PROJECTOR", "EASEL",
     "OVERHEAD PROJECTOR", "SPEAKER PHONE", "TABLE", "TV", "VCR",
     "VIDEO PHONE", "VEHICLE".  Resources can be specified in any
     registered language.

6. Internationalization Considerations

 Applications MUST generate iCalendar streams in the UTF-8 charset and
 MUST accept an iCalendar stream in the UTF-8 or US-ASCII charset.

7. Security Considerations

 Because calendaring and scheduling information is very privacy-
 sensitive, the protocol used for the transmission of calendaring and
 scheduling information should have capabilities to protect the
 information from possible threats, such as eavesdropping, replay,
 message insertion, deletion, modification, and man-in-the-middle
 attacks.
 As this document only defines the data format and media type of text/
 calendar that is independent of any calendar service or protocol, it
 is up to the actual protocol specifications such as iTIP [2446bis],

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 iMIP [2447bis], and "Calendaring Extensions to WebDAV (CalDAV)"
 [RFC4791] to describe the threats that the above attacks present, as
 well as ways in which to mitigate them.

8. IANA Considerations

8.1. iCalendar Media Type Registration

 The Calendaring and Scheduling Core Object Specification is intended
 for use as a MIME content type.
 To: ietf-types@iana.org
 Subject: Registration of media type text/calendar
 Type name:  text
 Subtype name:  calendar
 Required parameters:  none
 Optional parameters:  charset, method, component, and optinfo
    The "charset" parameter is defined in [RFC2046] for subtypes of
    the "text" media type.  It is used to indicate the charset used in
    the body part.  The charset supported by this revision of
    iCalendar is UTF-8.  The use of any other charset is deprecated by
    this revision of iCalendar; however, note that this revision
    requires that compliant applications MUST accept iCalendar streams
    using either the UTF-8 or US-ASCII charset.
    The "method" parameter is used to convey the iCalendar object
    method or transaction semantics for the calendaring and scheduling
    information.  It also is an identifier for the restricted set of
    properties and values of which the iCalendar object consists.  The
    parameter is to be used as a guide for applications interpreting
    the information contained within the body part.  It SHOULD NOT be
    used to exclude or require particular pieces of information unless
    the identified method definition specifically calls for this
    behavior.  Unless specifically forbidden by a particular method
    definition, a text/calendar content type can contain any set of
    properties permitted by the Calendaring and Scheduling Core Object
    Specification.  The "method" parameter MUST be specified and MUST
    be set to the same value as the "METHOD" component property of the
    iCalendar objects of the iCalendar stream if and only if the
    iCalendar objects in the iCalendar stream all have a "METHOD"
    component property set to the same value.

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    The value for the "method" parameter is defined as follows:
     method  = 1*(ALPHA / DIGIT / "-")
     ; IANA-registered iCalendar object method
    The "component" parameter conveys the type of iCalendar calendar
    component within the body part.  If the iCalendar object contains
    more than one calendar component type, then multiple component
    parameters MUST be specified.
    The value for the "component" parameter is defined as follows:
     component = "VEVENT"
               / "VTODO"
               / "VJOURNAL"
               / "VFREEBUSY"
               / "VTIMEZONE"
               / iana-token
               / x-name
    The "optinfo" parameter conveys optional information about the
    iCalendar object within the body part.  This parameter can only
    specify semantics already specified by the iCalendar object and
    that can be otherwise determined by parsing the body part.  In
    addition, the optional information specified by this parameter
    MUST be consistent with that information specified by the
    iCalendar object.  For example, it can be used to convey the
    "Attendee" response status to a meeting request.  The parameter
    value consists of a string value.
    The parameter can be specified multiple times.
    The value for the "optinfo" parameter is defined as follows:
     optinfo    = infovalue / qinfovalue
     infovalue  = iana-token / x-name
     qinfovalue = DQUOTE (infovalue) DQUOTE
 Encoding considerations:  This media type can contain 8bit
    characters, so the use of quoted-printable or base64 MIME Content-
    Transfer-Encodings might be necessary when iCalendar objects are
    transferred across protocols restricted to the 7bit repertoire.
    Note that a text valued property in the content entity can also
    have content encoding of special characters using a BACKSLASH
    character escapement technique.  This means that content values
    can end up being encoded twice.

Desruisseaux Standards Track [Page 150] RFC 5545 iCalendar September 2009

 Security considerations:  See Section 7.
 Interoperability considerations:  This media type is intended to
    define a common format for conveying calendaring and scheduling
    information between different systems.  It is heavily based on the
    earlier [VCAL] industry specification.
 Published specification:  This specification.
 Applications that use this media type:  This media type is designed
    for widespread use by Internet calendaring and scheduling
    applications.  In addition, applications in the workflow and
    document management area might find this content-type applicable.
    The iTIP [2446bis], iMIP [2447bis], and CalDAV [RFC4791] Internet
    protocols directly use this media type also.
 Additional information:
    Magic number(s):  None.
    File extension(s):  The file extension of "ics" is to be used to
       designate a file containing (an arbitrary set of) calendaring
       and scheduling information consistent with this MIME content
       type.
       The file extension of "ifb" is to be used to designate a file
       containing free or busy time information consistent with this
       MIME content type.
    Macintosh file type code(s):  The file type code of "iCal" is to
       be used in Apple MacIntosh operating system environments to
       designate a file containing calendaring and scheduling
       information consistent with this MIME media type.
       The file type code of "iFBf" is to be used in Apple MacIntosh
       operating system environments to designate a file containing
       free or busy time information consistent with this MIME media
       type.
 Person & email address to contact for further information:  See the
    "Author's Address" section of this document.
 Intended usage:  COMMON
 Restrictions on usage:  There are no restrictions on where this media
    type can be used.
 Author:  See the "Author's Address" section of this document.

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 Change controller:  IETF

8.2. New iCalendar Elements Registration

 This section defines the process to register new or modified
 iCalendar elements, that is, components, properties, parameters,
 value data types, and values, with IANA.

8.2.1. iCalendar Elements Registration Procedure

 The IETF will create a mailing list, icalendar@ietf.org, which can be
 used for public discussion of iCalendar elements proposals prior to
 registration.  Use of the mailing list is strongly encouraged.  The
 IESG will appoint a designated expert who will monitor the
 icalendar@ietf.org mailing list and review registrations.
 Registration of new iCalendar elements MUST be reviewed by the
 designated expert and published in an RFC.  A Standards Track RFC is
 REQUIRED for the registration of new value data types that modify
 existing properties, as well as for the registration of participation
 status values to be used in "VEVENT" calendar components.  A
 Standards Track RFC is also REQUIRED for registration of iCalendar
 elements that modify iCalendar elements previously documented in a
 Standards Track RFC.
 The registration procedure begins when a completed registration
 template, defined in the sections below, is sent to
 icalendar@ietf.org and iana@iana.org.  The designated expert is
 expected to tell IANA and the submitter of the registration within
 two weeks whether the registration is approved, approved with minor
 changes, or rejected with cause.  When a registration is rejected
 with cause, it can be re-submitted if the concerns listed in the
 cause are addressed.  Decisions made by the designated expert can be
 appealed to the IESG Applications Area Director, then to the IESG.
 They follow the normal appeals procedure for IESG decisions.

8.2.2. Registration Template for Components

 A component is defined by completing the following template.
 Component name:  The name of the component.
 Purpose:  The purpose of the component.  Give a short but clear
    description.
 Format definition:  The ABNF for the component definition needs to be
    specified.

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 Description:  Any special notes about the component, how it is to be
    used, etc.
 Example(s):  One or more examples of instances of the component need
    to be specified.

8.2.3. Registration Template for Properties

 A property is defined by completing the following template.
 Property name:  The name of the property.
 Purpose:  The purpose of the property.  Give a short but clear
    description.
 Value type:  Any of the valid value types for the property value need
    to be specified.  The default value type also needs to be
    specified.
 Property parameters:  Any of the valid property parameters for the
    property MUST be specified.
 Conformance:  The calendar components in which the property can
    appear MUST be specified.
 Description:  Any special notes about the property, how it is to be
    used, etc.
 Format definition:  The ABNF for the property definition needs to be
    specified.
 Example(s):  One or more examples of instances of the property need
    to be specified.

8.2.4. Registration Template for Parameters

 A parameter is defined by completing the following template.
 Parameter name:  The name of the parameter.
 Purpose:  The purpose of the parameter.  Give a short but clear
    description.
 Format definition:  The ABNF for the parameter definition needs to be
    specified.
 Description:  Any special notes about the parameter, how it is to be
    used, etc.

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 Example(s):  One or more examples of instances of the parameter need
    to be specified.

8.2.5. Registration Template for Value Data Types

 A value data type is defined by completing the following template.
 Value name:  The name of the value type.
 Purpose:  The purpose of the value type.  Give a short but clear
    description.
 Format definition:  The ABNF for the value type definition needs to
    be specified.
 Description:  Any special notes about the value type, how it is to be
    used, etc.
 Example(s):  One or more examples of instances of the value type need
    to be specified.

8.2.6. Registration Template for Values

 A value is defined by completing the following template.
 Value:  The value literal.
 Purpose:  The purpose of the value.  Give a short but clear
    description.
 Conformance:  The calendar properties and/or parameters that can take
    this value need to be specified.
 Example(s):  One or more examples of instances of the value need to
    be specified.
 The following is a fictitious example of a registration of an
 iCalendar value:
 Value:  TOP-SECRET
 Purpose:  This value is used to specify the access classification of
    top-secret calendar components.
 Conformance:  This value can be used with the "CLASS" property.

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 Example(s):  The following is an example of this value used with the
    "CLASS" property:
   CLASS:TOP-SECRET

8.3. Initial iCalendar Elements Registries

 The IANA created and maintains the following registries for iCalendar
 elements with pointers to appropriate reference documents.

8.3.1. Components Registry

 The following table has been used to initialize the components
 registry.
           +-----------+---------+-------------------------+
           | Component | Status  | Reference               |
           +-----------+---------+-------------------------+
           | VCALENDAR | Current | RFC 5545, Section 3.4   |
           |           |         |                         |
           | VEVENT    | Current | RFC 5545, Section 3.6.1 |
           |           |         |                         |
           | VTODO     | Current | RFC 5545, Section 3.6.2 |
           |           |         |                         |
           | VJOURNAL  | Current | RFC 5545, Section 3.6.3 |
           |           |         |                         |
           | VFREEBUSY | Current | RFC 5545, Section 3.6.4 |
           |           |         |                         |
           | VTIMEZONE | Current | RFC 5545, Section 3.6.5 |
           |           |         |                         |
           | VALARM    | Current | RFC 5545, Section 3.6.6 |
           |           |         |                         |
           | STANDARD  | Current | RFC 5545, Section 3.6.5 |
           |           |         |                         |
           | DAYLIGHT  | Current | RFC 5545, Section 3.6.5 |
           +-----------+---------+-------------------------+

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8.3.2. Properties Registry

 The following table is has been used to initialize the properties
 registry.
    +------------------+------------+----------------------------+
    | Property         | Status     | Reference                  |
    +------------------+------------+----------------------------+
    | CALSCALE         | Current    | RFC 5545, Section 3.7.1    |
    | METHOD           | Current    | RFC 5545, Section 3.7.2    |
    |                  |            |                            |
    | PRODID           | Current    | RFC 5545, Section 3.7.3    |
    |                  |            |                            |
    | VERSION          | Current    | RFC 5545, Section 3.7.4    |
    |                  |            |                            |
    | ATTACH           | Current    | RFC 5545, Section 3.8.1.1  |
    |                  |            |                            |
    | CATEGORIES       | Current    | RFC 5545, Section 3.8.1.2  |
    |                  |            |                            |
    | CLASS            | Current    | RFC 5545, Section 3.8.1.3  |
    |                  |            |                            |
    | COMMENT          | Current    | RFC 5545, Section 3.8.1.4  |
    |                  |            |                            |
    | DESCRIPTION      | Current    | RFC 5545, Section 3.8.1.5  |
    |                  |            |                            |
    | GEO              | Current    | RFC 5545, Section 3.8.1.6  |
    |                  |            |                            |
    | LOCATION         | Current    | RFC 5545, Section 3.8.1.7  |
    |                  |            |                            |
    | PERCENT-COMPLETE | Current    | RFC 5545, Section 3.8.1.8  |
    |                  |            |                            |
    | PRIORITY         | Current    | RFC 5545, Section 3.8.1.9  |
    |                  |            |                            |
    | RESOURCES        | Current    | RFC 5545, Section 3.8.1.10 |
    |                  |            |                            |
    | STATUS           | Current    | RFC 5545, Section 3.8.1.11 |
    |                  |            |                            |
    | SUMMARY          | Current    | RFC 5545, Section 3.8.1.12 |
    |                  |            |                            |
    | COMPLETED        | Current    | RFC 5545, Section 3.8.2.1  |
    |                  |            |                            |
    | DTEND            | Current    | RFC 5545, Section 3.8.2.2  |
    |                  |            |                            |
    | DUE              | Current    | RFC 5545, Section 3.8.2.3  |
    |                  |            |                            |
    | DTSTART          | Current    | RFC 5545, Section 3.8.2.4  |
    |                  |            |                            |
    | DURATION         | Current    | RFC 5545, Section 3.8.2.5  |

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    |                  |            |                            |
    | FREEBUSY         | Current    | RFC 5545, Section 3.8.2.6  |
    |                  |            |                            |
    | TRANSP           | Current    | RFC 5545, Section 3.8.2.7  |
    |                  |            |                            |
    | TZID             | Current    | RFC 5545, Section 3.8.3.1  |
    |                  |            |                            |
    | TZNAME           | Current    | RFC 5545, Section 3.8.3.2  |
    |                  |            |                            |
    | TZOFFSETFROM     | Current    | RFC 5545, Section 3.8.3.3  |
    |                  |            |                            |
    | TZOFFSETTO       | Current    | RFC 5545, Section 3.8.3.4  |
    |                  |            |                            |
    | TZURL            | Current    | RFC 5545, Section 3.8.3.5  |
    |                  |            |                            |
    | ATTENDEE         | Current    | RFC 5545, Section 3.8.4.1  |
    |                  |            |                            |
    | CONTACT          | Current    | RFC 5545, Section 3.8.4.2  |
    |                  |            |                            |
    | ORGANIZER        | Current    | RFC 5545, Section 3.8.4.3  |
    |                  |            |                            |
    | RECURRENCE-ID    | Current    | RFC 5545, Section 3.8.4.4  |
    |                  |            |                            |
    | RELATED-TO       | Current    | RFC 5545, Section 3.8.4.5  |
    |                  |            |                            |
    | URL              | Current    | RFC 5545, Section 3.8.4.6  |
    |                  |            |                            |
    | UID              | Current    | RFC 5545, Section 3.8.4.7  |
    |                  |            |                            |
    | EXDATE           | Current    | RFC 5545, Section 3.8.5.1  |
    |                  |            |                            |
    | EXRULE           | Deprecated | [RFC2445], Section 4.8.5.2 |
    |                  |            |                            |
    | RDATE            | Current    | RFC 5545, Section 3.8.5.2  |
    |                  |            |                            |
    | RRULE            | Current    | RFC 5545, Section 3.8.5.3  |
    |                  |            |                            |
    | ACTION           | Current    | RFC 5545, Section 3.8.6.1  |
    |                  |            |                            |
    | REPEAT           | Current    | RFC 5545, Section 3.8.6.2  |
    |                  |            |                            |
    | TRIGGER          | Current    | RFC 5545, Section 3.8.6.3  |
    |                  |            |                            |
    | CREATED          | Current    | RFC 5545, Section 3.8.7.1  |
    |                  |            |                            |
    | DTSTAMP          | Current    | RFC 5545, Section 3.8.7.2  |
    |                  |            |                            |
    | LAST-MODIFIED    | Current    | RFC 5545, Section 3.8.7.3  |

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    |                  |            |                            |
    | SEQUENCE         | Current    | RFC 5545, Section 3.8.7.4  |
    |                  |            |                            |
    | REQUEST-STATUS   | Current    | RFC 5545, Section 3.8.8.3  |
    +------------------+------------+----------------------------+

8.3.3. Parameters Registry

 The following table has been used to initialize the parameters
 registry.
        +----------------+---------+--------------------------+
        | Parameter      | Status  | Reference                |
        +----------------+---------+--------------------------+
        | ALTREP         | Current | RFC 5545, Section 3.2.1  |
        |                |         |                          |
        | CN             | Current | RFC 5545, Section 3.2.2  |
        |                |         |                          |
        | CUTYPE         | Current | RFC 5545, Section 3.2.3  |
        |                |         |                          |
        | DELEGATED-FROM | Current | RFC 5545, Section 3.2.4  |
        |                |         |                          |
        | DELEGATED-TO   | Current | RFC 5545, Section 3.2.5  |
        |                |         |                          |
        | DIR            | Current | RFC 5545, Section 3.2.6  |
        |                |         |                          |
        | ENCODING       | Current | RFC 5545, Section 3.2.7  |
        |                |         |                          |
        | FMTTYPE        | Current | RFC 5545, Section 3.2.8  |
        |                |         |                          |
        | FBTYPE         | Current | RFC 5545, Section 3.2.9  |
        |                |         |                          |
        | LANGUAGE       | Current | RFC 5545, Section 3.2.10 |
        |                |         |                          |
        | MEMBER         | Current | RFC 5545, Section 3.2.11 |
        |                |         |                          |
        | PARTSTAT       | Current | RFC 5545, Section 3.2.12 |
        |                |         |                          |
        | RANGE          | Current | RFC 5545, Section 3.2.13 |
        |                |         |                          |
        | RELATED        | Current | RFC 5545, Section 3.2.14 |
        |                |         |                          |
        | RELTYPE        | Current | RFC 5545, Section 3.2.15 |
        |                |         |                          |
        | ROLE           | Current | RFC 5545, Section 3.2.16 |
        |                |         |                          |
        | RSVP           | Current | RFC 5545, Section 3.2.17 |
        |                |         |                          |

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        | SENT-BY        | Current | RFC 5545, Section 3.2.18 |
        |                |         |                          |
        | TZID           | Current | RFC 5545, Section 3.2.19 |
        |                |         |                          |
        | VALUE          | Current | RFC 5545, Section 3.2.20 |
        +----------------+---------+--------------------------+

8.3.4. Value Data Types Registry

 The following table has been used to initialize the value data types
 registry.
       +-----------------+---------+--------------------------+
       | Value Data Type | Status  | Reference                |
       +-----------------+---------+--------------------------+
       | BINARY          | Current | RFC 5545, Section 3.3.1  |
       |                 |         |                          |
       | BOOLEAN         | Current | RFC 5545, Section 3.3.2  |
       |                 |         |                          |
       | CAL-ADDRESS     | Current | RFC 5545, Section 3.3.3  |
       |                 |         |                          |
       | DATE            | Current | RFC 5545, Section 3.3.4  |
       |                 |         |                          |
       | DATE-TIME       | Current | RFC 5545, Section 3.3.5  |
       |                 |         |                          |
       | DURATION        | Current | RFC 5545, Section 3.3.6  |
       |                 |         |                          |
       | FLOAT           | Current | RFC 5545, Section 3.3.7  |
       |                 |         |                          |
       | INTEGER         | Current | RFC 5545, Section 3.3.8  |
       |                 |         |                          |
       | PERIOD          | Current | RFC 5545, Section 3.3.9  |
       |                 |         |                          |
       | RECUR           | Current | RFC 5545, Section 3.3.10 |
       |                 |         |                          |
       | TEXT            | Current | RFC 5545, Section 3.3.11 |
       |                 |         |                          |
       | TIME            | Current | RFC 5545, Section 3.3.12 |
       |                 |         |                          |
       | URI             | Current | RFC 5545, Section 3.3.13 |
       |                 |         |                          |
       | UTC-OFFSET      | Current | RFC 5545, Section 3.3.14 |
       +-----------------+---------+--------------------------+

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8.3.5. Calendar User Types Registry

 The following table has been used to initialize the calendar user
 types registry.
      +--------------------+---------+-------------------------+
      | Calendar User Type | Status  | Reference               |
      +--------------------+---------+-------------------------+
      | INDIVIDUAL         | Current | RFC 5545, Section 3.2.3 |
      |                    |         |                         |
      | GROUP              | Current | RFC 5545, Section 3.2.3 |
      |                    |         |                         |
      | RESOURCE           | Current | RFC 5545, Section 3.2.3 |
      |                    |         |                         |
      | ROOM               | Current | RFC 5545, Section 3.2.3 |
      |                    |         |                         |
      | UNKNOWN            | Current | RFC 5545, Section 3.2.3 |
      +--------------------+---------+-------------------------+

8.3.6. Free/Busy Time Types Registry

 The following table has been used to initialize the free/busy time
 types registry.
      +---------------------+---------+-------------------------+
      | Free/Busy Time Type | Status  | Reference               |
      +---------------------+---------+-------------------------+
      | FREE                | Current | RFC 5545, Section 3.2.9 |
      |                     |         |                         |
      | BUSY                | Current | RFC 5545, Section 3.2.9 |
      |                     |         |                         |
      | BUSY-UNAVAILABLE    | Current | RFC 5545, Section 3.2.9 |
      |                     |         |                         |
      | BUSY-TENTATIVE      | Current | RFC 5545, Section 3.2.9 |
      +---------------------+---------+-------------------------+

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8.3.7. Participation Statuses Registry

 The following table has been used to initialize the participation
 statuses registry.
      +--------------------+---------+--------------------------+
      | Participant Status | Status  | Reference                |
      +--------------------+---------+--------------------------+
      | NEEDS-ACTION       | Current | RFC 5545, Section 3.2.12 |
      |                    |         |                          |
      | ACCEPTED           | Current | RFC 5545, Section 3.2.12 |
      |                    |         |                          |
      | DECLINED           | Current | RFC 5545, Section 3.2.12 |
      |                    |         |                          |
      | TENTATIVE          | Current | RFC 5545, Section 3.2.12 |
      |                    |         |                          |
      | DELEGATED          | Current | RFC 5545, Section 3.2.12 |
      |                    |         |                          |
      | COMPLETED          | Current | RFC 5545, Section 3.2.12 |
      |                    |         |                          |
      | IN-PROCESS         | Current | RFC 5545, Section 3.2.12 |
      +--------------------+---------+--------------------------+

8.3.8. Relationship Types Registry

 The following table has been used to initialize the relationship
 types registry.
      +-------------------+---------+--------------------------+
      | Relationship Type | Status  | Reference                |
      +-------------------+---------+--------------------------+
      | CHILD             | Current | RFC 5545, Section 3.2.15 |
      |                   |         |                          |
      | PARENT            | Current | RFC 5545, Section 3.2.15 |
      |                   |         |                          |
      | SIBLING           | Current | RFC 5545, Section 3.2.15 |
      +-------------------+---------+--------------------------+

Desruisseaux Standards Track [Page 161] RFC 5545 iCalendar September 2009

8.3.9. Participation Roles Registry

 The following table has been used to initialize the participation
 roles registry.
       +-----------------+---------+--------------------------+
       | Role Type       | Status  | Reference                |
       +-----------------+---------+--------------------------+
       | CHAIR           | Current | RFC 5545, Section 3.2.16 |
       |                 |         |                          |
       | REQ-PARTICIPANT | Current | RFC 5545, Section 3.2.16 |
       |                 |         |                          |
       | OPT-PARTICIPANT | Current | RFC 5545, Section 3.2.16 |
       |                 |         |                          |
       | NON-PARTICIPANT | Current | RFC 5545, Section 3.2.16 |
       +-----------------+---------+--------------------------+

8.3.10. Actions Registry

 The following table has been used to initialize the actions registry.
        +-----------+------------+----------------------------+
        | Action    | Status     | Reference                  |
        +-----------+------------+----------------------------+
        | AUDIO     | Current    | RFC 5545, Section 3.8.6.1  |
        |           |            |                            |
        | DISPLAY   | Current    | RFC 5545, Section 3.8.6.1  |
        |           |            |                            |
        | EMAIL     | Current    | RFC 5545, Section 3.8.6.1  |
        |           |            |                            |
        | PROCEDURE | Deprecated | [RFC2445], Section 4.8.6.1 |
        +-----------+------------+----------------------------+

8.3.11. Classifications Registry

 The following table has been used to initialize the classifications
 registry.
       +----------------+---------+---------------------------+
       | Classification | Status  | Reference                 |
       +----------------+---------+---------------------------+
       | PUBLIC         | Current | RFC 5545, Section 3.8.1.3 |
       |                |         |                           |
       | PRIVATE        | Current | RFC 5545, Section 3.8.1.3 |
       |                |         |                           |
       | CONFIDENTIAL   | Current | RFC 5545, Section 3.8.1.3 |
       +----------------+---------+---------------------------+

Desruisseaux Standards Track [Page 162] RFC 5545 iCalendar September 2009

8.3.12. Methods Registry

 No values are defined in this document for the "METHOD" property.

9. Acknowledgments

 The editor of this document wishes to thank Frank Dawson and Derik
 Stenerson, the original authors of RFC 2445, as well as the following
 individuals who have participated in the drafting, review, and
 discussion of this memo:
 Joe Abley, Hervey Allen, Steve Allen, Jay Batson, Oliver Block,
 Stephane Bortzmeyer, Chris Bryant, Tantek Celik, Mark Crispin, Cyrus
 Daboo, Mike Douglass, Andrew N. Dowden, Lisa Dusseault, Lars Eggert,
 Gren Eliot, Pasi Eronen, Ben Fortuna, Ned Freed, Neal Gafter, Ted
 Hardie, Tim Hare, Jeffrey Harris, Helge Hess, Paul B. Hill, Thomas
 Hnetila, Russ Housley, Leif Johansson, Ciny Joy, Bruce Kahn, Reinhold
 Kainhofer, Martin Kiff, Patrice Lapierre, Michiel van Leeuwen,
 Jonathan Lennox, Jeff McCullough, Bill McQuillan, Alexey Melnikov,
 John W. Noerenberg II, Chuck Norris, Mark Paterson, Simon Pilette,
 Arnaud Quillaud, Robert Ransdell, Julian F. Reschke, Caleb
 Richardson, Sam Roberts, Dan Romascanu, Mike Samuel, George Sexton,
 Nigel Swinson, Clint Talbert, Simon Vaillancourt, Magnus Westerlund,
 and Sandy Wills.
 A special thanks to the working group chairs Aki Niemi and Eliot Lear
 for their support and guidance.
 The editor would also like to thank the Calendaring and Scheduling
 Consortium for advice with this specification, and for organizing
 interoperability testing events to help refine it.

Desruisseaux Standards Track [Page 163] RFC 5545 iCalendar September 2009

10. References

10.1. Normative References

 [ISO.8601.2004]        International Organization for
                        Standardization, "Data elements and
                        interchange formats -- Information interchange
                        -- Representation of dates and times", 2004.
 [ISO.9070.1991]        International Organization for
                        Standardization, "Information Technology_SGML
                        Support Facilities -- Registration Procedures
                        for Public Text Owner Identifiers, Second
                        Edition", April 1991.
 [RFC2045]              Freed, N. and N. Borenstein, "Multipurpose
                        Internet Mail Extensions (MIME) Part One:
                        Format of Internet Message Bodies", RFC 2045,
                        November 1996.
 [RFC2046]              Freed, N. and N. Borenstein, "Multipurpose
                        Internet Mail Extensions (MIME) Part Two:
                        Media Types", RFC 2046, November 1996.
 [RFC2119]              Bradner, S., "Key words for use in RFCs to
                        Indicate Requirement Levels", BCP 14,
                        RFC 2119, March 1997.
 [RFC2368]              Hoffman, P., Masinter, L., and J. Zawinski,
                        "The mailto URL scheme", RFC 2368, July 1998.
 [RFC3629]              Yergeau, F., "UTF-8, a transformation format
                        of ISO 10646", STD 63, RFC 3629,
                        November 2003.
 [RFC3986]              Berners-Lee, T., Fielding, R., and L.
                        Masinter, "Uniform Resource Identifier (URI):
                        Generic Syntax", STD 66, RFC 3986,
                        January 2005.
 [RFC4288]              Freed, N. and J. Klensin, "Media Type
                        Specifications and Registration Procedures",
                        BCP 13, RFC 4288, December 2005.
 [RFC4648]              Josefsson, S., "The Base16, Base32, and Base64
                        Data Encodings", RFC 4648, October 2006.

Desruisseaux Standards Track [Page 164] RFC 5545 iCalendar September 2009

 [RFC5234]              Crocker, D. and P. Overell, "Augmented BNF for
                        Syntax Specifications: ABNF", STD 68,
                        RFC 5234, January 2008.
 [RFC5646]              Phillips, A., Ed., and M. Davis, Ed., "Tags
                        for Identifying Languages", BCP 47, RFC 5646,
                        September 2009.
 [US-ASCII]             American National Standards Institute, "Coded
                        Character Set - 7-bit American Standard Code
                        for Information Interchange", ANSI X3.4, 1986.

10.2. Informative References

 [2446bis]              Daboo, C., "iCalendar Transport-Independent
                        Interoperability Protocol (iTIP)", Work
                        in Progress, April 2009.
 [2447bis]              Melnikov, A., "iCalendar Message-Based
                        Interoperability Protocol (iMIP)", Work
                        in Progress, June 2008.
 [ANSI INCITS 61-1986]  International Committee for Information
                        Technology, "Representation of Geographic
                        Point Locations for Information Interchange
                        (formerly ANSI X3.61-1986 (R1997))", ANSI
                        INCITS 61-1986 (R2007), 2007.
 [RFC1738]              Berners-Lee, T., Masinter, L., and M.
                        McCahill, "Uniform Resource Locators (URL)",
                        RFC 1738, December 1994.
 [RFC2392]              Levinson, E., "Content-ID and Message-ID
                        Uniform Resource Locators", RFC 2392,
                        August 1998.
 [RFC2397]              Masinter, L., "The "data" URL scheme",
                        RFC 2397, August 1998.
 [RFC2425]              Howes, T., Smith, M., and F. Dawson, "A MIME
                        Content-Type for Directory Information",
                        RFC 2425, September 1998.
 [RFC2426]              Dawson, F. and T. Howes, "vCard MIME Directory
                        Profile", RFC 2426, September 1998.

Desruisseaux Standards Track [Page 165] RFC 5545 iCalendar September 2009

 [RFC2445]              Dawson, F. and Stenerson, D., "Internet
                        Calendaring and Scheduling Core Object
                        Specification (iCalendar)", RFC 2445,
                        November 1998.
 [RFC2616]              Fielding, R., Gettys, J., Mogul, J., Frystyk,
                        H., Masinter, L., Leach, P., and T. Berners-
                        Lee, "Hypertext Transfer Protocol --
                        HTTP/1.1", RFC 2616, June 1999.
 [RFC2818]              Rescorla, E., "HTTP Over TLS", RFC 2818,
                        May 2000.
 [RFC4516]              Smith, M. and T. Howes, "Lightweight Directory
                        Access Protocol (LDAP): Uniform Resource
                        Locator", RFC 4516, June 2006.
 [RFC4791]              Daboo, C., Desruisseaux, B., and L. Dusseault,
                        "Calendaring Extensions to WebDAV (CalDAV)",
                        RFC 4791, March 2007.
 [TZDB]                 Eggert, P. and A.D. Olson, "Sources for Time
                        Zone and Daylight Saving Time Data",
                        July 2009,
                        <http://www.twinsun.com/tz/tz-link.htm>.
 [VCAL]                 Internet Mail Consortium, "vCalendar: The
                        Electronic Calendaring and Scheduling Exchange
                        Format", September 1996,
                        <http://www.imc.org/pdi/vcal-10.txt>.

Desruisseaux Standards Track [Page 166] RFC 5545 iCalendar September 2009

Appendix A. Differences from RFC 2445

 This appendix contains a list of changes that have been made in the
 Internet Calendaring and Scheduling Core Object Specification from
 RFC 2445.

A.1. New Restrictions

 1.  The "DTSTART" property SHOULD be synchronized with the recurrence
     rule, if specified.
 2.  The "RRULE" property SHOULD NOT occur more than once in a
     component.
 3.  The BYHOUR, BYMINUTE, and BYSECOND rule parts MUST NOT be
     specified in the "RRULE" property when the "DTSTART" property is
     specified as a DATE value.
 4.  The value type of the "DTEND" or "DUE" properties MUST match the
     value type of "DTSTART" property.
 5.  The "DURATION" property can no longer appear in "VFREEBUSY"
     components.

A.2. Restrictions Removed

 1.  The "DTSTART" and "DTEND" properties are no longer required to be
     specified as date with local time and time zone reference when
     used with a recurrence rule.

A.3. Deprecated Features

 1.  The "EXRULE" property can no longer be specified in a component.
 2.  The "THISANDPRIOR" value can no longer be used with the "RANGE"
     parameter.
 3.  The "PROCEDURE" value can no longer be used with the "ACTION"
     property.
 4.  The value type RECUR no longer allows multiple values to be
     specified by a COMMA-separated list of values.
 5.  x-name rule parts can no longer be specified in properties of
     RECUR value type (e.g., "RRULE"). x-param can be used on RECUR
     value type properties instead.

Desruisseaux Standards Track [Page 167] RFC 5545 iCalendar September 2009

Author's Address

 Bernard Desruisseaux (editor)
 Oracle Corporation
 600 blvd. de Maisonneuve West
 Suite 1900
 Montreal, QC  H3A 3J2
 CANADA
 EMail: bernard.desruisseaux@oracle.com
 URI:   http://www.oracle.com/

Desruisseaux Standards Track [Page 168]

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