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rfc:rfc7595

Internet Engineering Task Force (IETF) D. Thaler, Ed. Request for Comments: 7595 Microsoft Obsoletes: 4395 T. Hansen BCP: 35 AT&T Laboratories Category: Best Current Practice T. Hardie ISSN: 2070-1721 Google

                                                             June 2015
       Guidelines and Registration Procedures for URI Schemes

Abstract

 This document updates the guidelines and recommendations, as well as
 the IANA registration processes, for the definition of Uniform
 Resource Identifier (URI) schemes.  It obsoletes RFC 4395.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7595.

Copyright Notice

 Copyright (c) 2015 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 Simplified BSD License.

Thaler, et al. Best Current Practice [Page 1] RFC 7595 URI Scheme Guidelines June 2015

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.1.  URIs and IRIs . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
 3.  Requirements for Permanent Scheme Definitions . . . . . . . .   4
   3.1.  Demonstrable, New, Long-Lived Utility . . . . . . . . . .   4
   3.2.  Syntactic Compatibility . . . . . . . . . . . . . . . . .   4
   3.3.  Well Defined  . . . . . . . . . . . . . . . . . . . . . .   5
   3.4.  Definition of Operations  . . . . . . . . . . . . . . . .   6
   3.5.  Context of Use  . . . . . . . . . . . . . . . . . . . . .   6
   3.6.  Internationalization and Character Encoding . . . . . . .   7
   3.7.  Clear Security and Privacy Considerations . . . . . . . .   7
   3.8.  Scheme Name Considerations  . . . . . . . . . . . . . . .   8
   3.9.  Interoperability Considerations . . . . . . . . . . . . .   9
 4.  Guidelines for Provisional URI Scheme Registration  . . . . .   9
 5.  Guidelines for Historical URI Scheme Registration . . . . . .  10
 6.  Guidelines for Private URI Scheme Use . . . . . . . . . . . .  10
 7.  URI Scheme Registration Procedure . . . . . . . . . . . . . .  10
   7.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.2.  Registration Procedures . . . . . . . . . . . . . . . . .  11
   7.3.  Change Control  . . . . . . . . . . . . . . . . . . . . .  13
   7.4.  URI Scheme Registration Template  . . . . . . . . . . . .  13
 8.  The "example" URI Scheme  . . . . . . . . . . . . . . . . . .  14
   8.1.  "example" URI Scheme Registration Request . . . . . . . .  15
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
 10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
 11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
   11.2.  Informative References . . . . . . . . . . . . . . . . .  17
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
 Contributor . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1. Introduction

 The Uniform Resource Identifier (URI) protocol element and generic
 syntax is defined by [RFC3986].  Each URI begins with a scheme name,
 as defined by Section 3.1 of RFC 3986, that refers to a specification
 for identifiers within that scheme.  The URI syntax provides a
 federated and extensible naming system, where each scheme's
 specification can further restrict the syntax and define the
 semantics of identifiers using that scheme.
 This document obsoletes [RFC4395], which in turn obsoleted [RFC2717]
 and [RFC2718].  Recent documents have used the term "URI" for all
 resource identifiers, avoiding the term "URL" and reserving the term
 "URN" explicitly for those URIs using the "urn" scheme name

Thaler, et al. Best Current Practice [Page 2] RFC 7595 URI Scheme Guidelines June 2015

 [RFC2141].  URN "namespaces" [RFC3406] are specific to the "urn"
 scheme and are not covered explicitly by this specification.
 This document provides updated guidelines for the definition of new
 schemes, for consideration by those who are defining, registering, or
 evaluating those definitions.  In addition, this document provides an
 updated process and mechanism for registering schemes within the IANA
 URI Schemes registry.  There is a single namespace for registered
 schemes.  The intent of the registry is to:
 o  provide a central point of discovery for established URI scheme
    names and easy location of defining documents for schemes;
 o  discourage multiple separate uses of the same scheme name;
 o  help those proposing new scheme names to discern established
    trends and conventions and to avoid names that might be confused
    with existing ones; and
 o  encourage registration by setting a low barrier for registration.

1.1. URIs and IRIs

 As originally defined, URIs only allowed a limited repertoire of
 characters chosen from US-ASCII.  An Internationalized Resource
 Identifier (IRI), as defined by [RFC3987], extends the URI syntax to
 allow characters from a much greater repertoire to accommodate
 resource identifiers from the world's languages.  RFC 3987 [RFC3987]
 also defined a mapping between URIs and IRIs.  IRIs use the same
 scheme names as URIs.  Thus, there is no separate independent
 registry or registration process for IRI schemes: the URI Schemes
 registry is used for both URIs and IRIs.  Those who wish to describe
 resource identifiers that are useful as IRIs should define the
 corresponding URI syntax and note that the IRI usage follows the
 rules and transformations defined in [RFC3987].

2. Terminology

 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 document distinguishes between a "scheme specification", which
 is a document defining the syntax and semantics of a scheme, and a
 "scheme registration request", which is the completed template
 submitted to IANA.  The term "scheme definition" refers generically
 to the syntax and semantics of a scheme and is typically documented
 in a scheme specification.

Thaler, et al. Best Current Practice [Page 3] RFC 7595 URI Scheme Guidelines June 2015

3. Requirements for Permanent Scheme Definitions

 This section gives considerations for new schemes.  Meeting these
 guidelines is REQUIRED for 'permanent' scheme registration.
 'Permanent' status is appropriate for, but not limited to, use in
 standards.  For URI schemes defined or normatively referenced by IETF
 Standards Track documents, 'permanent' registration status is
 REQUIRED.
 [RFC3986] defines the overall syntax for URIs as:
             URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
 A scheme definition cannot override the overall syntax for URIs.  For
 example, this means that fragment identifiers cannot be reused
 outside the generic syntax restrictions and that fragment identifiers
 are not scheme specific.  A scheme definition must specify the scheme
 name and the syntax of the scheme-specific part, which is clarified
 as follows:
               URI = scheme ":" scheme-specific-part [ "#" fragment ]
               scheme-specific-part = hier-part [ "?" query ]

3.1. Demonstrable, New, Long-Lived Utility

 In general, the use and deployment of new schemes in the Internet
 infrastructure can be costly; some parts of URI processing are often
 scheme dependent.  Introducing a new scheme might require additional
 software not only for client software and user agents but also in
 additional parts of the network infrastructure (gateways, proxies,
 caches) [W3CWebArch].  Since scheme names share a single, global
 namespace, it is desirable to avoid contention over use of short,
 mnemonic scheme names.  New schemes ought to have utility to the
 Internet community beyond that available with already registered
 schemes.  The scheme specification SHOULD discuss the utility of the
 scheme being registered.

3.2. Syntactic Compatibility

 [RFC3986] defines the generic syntax for all URI schemes, along with
 the syntax of common URI components that are used by many URI schemes
 to define hierarchical identifiers.  [RFC3987] extended this generic
 syntax to cover IRIs.  All scheme specifications MUST define their
 own URI <scheme-specific-part> syntax.  Care must be taken to ensure

Thaler, et al. Best Current Practice [Page 4] RFC 7595 URI Scheme Guidelines June 2015

 that all strings matching their scheme-specific syntax will also
 match the <absolute-URI> grammar described in [RFC3986].
 New schemes SHOULD reuse the common URI components of [RFC3986] for
 the definition of hierarchical naming schemes.  If there is a strong
 reason for a scheme not to use the hierarchical syntax, then the new
 scheme definition SHOULD follow the syntax of similar previously
 registered schemes.
 Schemes that are not intended for use with relative URIs SHOULD avoid
 use of the forward slash "/" character in order to avoid unintended
 processing, such as resolution of "." and ".." (dot segments).
 Schemes SHOULD avoid improper use of "//".  The use of double slashes
 in the first part of a URI is not a stylistic indicator that what
 follows is a URI: double slashes are intended for use ONLY when the
 syntax of the <scheme-specific-part> contains a hierarchical
 structure.  In URIs from such schemes, the use of double slashes
 indicates that what follows is the top hierarchical element for a
 naming authority (Section 3.2 of RFC 3986 has more details).  Schemes
 that do not contain a conformant hierarchical structure in their
 <scheme-specific-part> SHOULD NOT use double slashes following the
 "<scheme>:" string.
 New schemes SHOULD clearly define the role of reserved characters
 (see Section 2.2 of [RFC3986]) in URIs of the scheme being defined.
 The syntax of the new scheme should be clear about which of the
 "reserved" set of characters are used as delimiters within the URIs
 of the new scheme, and when those characters must be escaped, versus
 when they can be used without escaping.

3.3. Well Defined

 While URIs might or might not be defined as locators in practice, a
 scheme definition itself MUST be clear as to how it is expected to
 function.  Schemes that are not intended to be used as locators
 SHOULD describe how the resource identified can be determined or
 accessed by software that obtains a URI of that scheme.
 For schemes that function as locators, it is important that the
 mechanism of resource location be clearly defined.  This might mean
 different things depending on the nature of the scheme.
 In many cases, new schemes are defined as ways to translate between
 other namespaces or protocols and the general framework of URIs.  For
 example, the "ftp" scheme translates into the FTP protocol while the
 "mid" scheme translates into a Message-ID identifier of an email
 message.  For such schemes, the description of the mapping SHOULD be

Thaler, et al. Best Current Practice [Page 5] RFC 7595 URI Scheme Guidelines June 2015

 complete and in sufficient detail so that the mapping in both
 directions is clear: how to map from a URI into an identifier or set
 of protocol actions or name in the target namespace, and how legal
 values in the base namespace, or legal protocol interactions, are
 represented in a valid URI.  See Section 3.6 for guidelines for
 encoding strings or sequences of bytes within valid character
 sequences in a URI.  If not all legal values or protocol interactions
 of the base standard can be represented using the scheme, the
 definition SHOULD be clear about which subset is allowed and why.

3.4. Definition of Operations

 As part of the definition of how a URI identifies a resource, a
 scheme definition SHOULD define the applicable set of operations that
 can be performed on a resource using the URI as its identifier.  A
 model for this is HTTP methods; an HTTP resource can be operated on
 by GET, POST, PUT, and a number of other methods available through
 the HTTP protocol.  The scheme definition SHOULD describe all well-
 defined operations on the resource identifier and what they are
 supposed to do.
 Some schemes don't fit into the "information access" paradigm of
 URIs.  For example, "telnet" provides location information for
 initiating a bidirectional data stream to a remote host; the only
 operation defined is to initiate the connection.  In any case, the
 operations appropriate for a scheme SHOULD be documented.
 Note: It is perfectly valid to say that "no operation apart from GET
 is defined for this URI."  It is also valid to say that "there's only
 one operation defined for this URI, and it's not very GET-like."  The
 important point is that what is defined on this scheme is described.
 Scheme definitions SHOULD define a "default" operation for when a URI
 is invoked (or "dereferenced") by an application.  For example, a
 common "default" operation today is to launch an application
 associated with the scheme name and let it use the other URI
 components as inputs to do something.  The default invocation, or
 dereferencing, of a URI SHOULD be "safe" in the sense described by
 Section 3.4 of [W3CWebArch]; i.e., performing such an invocation
 should not incur any additional obligations by doing so.

3.5. Context of Use

 In general, URIs are used within a broad range of protocols and
 applications.  For example, URIs are commonly used within hypertext
 documents as references to other resources.  In some cases, a scheme
 is intended for use within a different, specific set of protocols or
 applications.  If so, the scheme definition SHOULD describe the

Thaler, et al. Best Current Practice [Page 6] RFC 7595 URI Scheme Guidelines June 2015

 intended use and include references to documentation that define the
 applications and/or protocols cited.  This does not obviate the need
 for documentation on applications and/or protocols to discuss URI
 schemes relevant to them.

3.6. Internationalization and Character Encoding

 When describing schemes in which (some of) the elements of the URI
 are actually representations of human-readable text, care should be
 taken not to introduce unnecessary variety in the ways in which
 characters are encoded into octets and then into URI characters; see
 [RFC3987] and Section 2.5 (especially the last paragraph) of
 [RFC3986] for guidelines.  If URIs of a scheme contain any text
 fields, the scheme definition MUST describe the ways in which
 characters are encoded and any compatibility issues with IRIs of the
 scheme.
 The scheme specification SHOULD be as restrictive as possible
 regarding what characters are allowed in the URI because some
 characters can create several different security issues (see, for
 example, [RFC4690]).
 Percent-encoded character sequences are automatically included by
 definition for characters given in IRI productions.  This means that
 if you want to restrict the URI percent-encoded forms in some way,
 you must restrict the Unicode forms that would lead to them.  In most
 cases, it is advisable to define the actual characters allowed in an
 IRI production in order to allow the 'pct-encoded' definition from
 Section 2.1 of [RFC3986] at the same places and to add prose that
 limits percent escapes to those that can be created by converting
 valid UTF-8 character sequences to percent-encoding.

3.7. Clear Security and Privacy Considerations

 Definitions of schemes MUST be accompanied by a clear analysis of the
 security and privacy implications for systems that use the scheme;
 this follows the practice of Security Consideration sections within
 IANA registrations [RFC5226].
 In particular, Section 7 of RFC 3986 [RFC3986] describes general
 security considerations for URIs while [RFC3987] gives those for
 IRIs.  The definition of an individual scheme should note which of
 these apply to the specified scheme, in addition to any more scheme-
 specific concerns.  For example, if the scheme-specific part is
 privacy sensitive, then that should be documented.

Thaler, et al. Best Current Practice [Page 7] RFC 7595 URI Scheme Guidelines June 2015

3.8. Scheme Name Considerations

 Section 3.1 of RFC 3986 defines the syntax of a URI scheme name; this
 syntax remains the same for IRIs.  New scheme registrations MUST
 follow this syntax, which only allows a limited repertoire of
 characters (taken from US-ASCII).  Although the syntax for the scheme
 name in URIs is case insensitive, the scheme name itself MUST be
 registered using lowercase letters.
 Scheme names SHOULD be short but also sufficiently descriptive and
 distinguished to avoid problems.
 Schemes SHOULD NOT use names or other symbols that might cause
 problems with rights to use the name in IETF specifications and
 Internet protocols.  For example, be careful with trademark and
 service mark names.  (See Section 3.4 of [RFC5378]).
 Schemes SHOULD NOT use names that are either very general purpose or
 associated in the community with some other application or protocol.
 Schemes also SHOULD NOT use names that are overly general or
 grandiose in scope (e.g., that allude to their "universal" or
 "standard" nature).
 A scheme name is not a "protocol."  However, like a service name as
 defined in Section 5 of [RFC6335], it often identifies a particular
 protocol or application.  If a scheme name has a one-to-one
 correspondence with a service name, then the names SHOULD be the
 same.
 Some organizations desire their own namespace for URI scheme names
 for private use (see Section 6).  In doing so, it is important to
 prevent collisions and to make it possible to identify the owner of a
 private-use scheme.  To accomplish these two goals, such
 organizations SHOULD use a prefix based on their domain name,
 expressed in reverse order.  For example, a URI scheme name of
 com.example.mything might be used by the organization that owns the
 example.com domain name.  Care must be taken, however, if the
 organization later loses the domain name embedded in their scheme
 names since domain name registrations are not permanent.  To
 associate the private-use scheme name with the original organization,
 the private-use scheme can be registered using the registration
 procedure in Section 7.
 Furthermore, to prevent collisions with private-use scheme names, new
 scheme names registered MUST NOT contain a "." unless actually
 constructed from a reversed domain name.

Thaler, et al. Best Current Practice [Page 8] RFC 7595 URI Scheme Guidelines June 2015

3.9. Interoperability Considerations

 If the person or group registering the scheme is aware of any details
 regarding the scheme that might impact interoperability, identify
 them, for example, proprietary or uncommon encoding methods, or
 incompatibility with types or versions of any underlying protocol.

4. Guidelines for Provisional URI Scheme Registration

 'Provisional' registration can be used for schemes that are not part
 of any standard but that are intended for use (or observed to be in
 use) that is not limited to a private environment within a single
 organization.  'Provisional' registration can also be used as an
 intermediate step on the way to 'permanent' registration, e.g.,
 before the scheme specification is finalized as a standard.
 For a 'provisional' registration, the following apply:
 o  The scheme name must meet the syntactic requirements of
    Section 3.8.
 o  There must not already be an entry with the same scheme name.  In
    the unfortunate case that there are multiple, different uses of
    the same scheme name, the Designated Expert can approve a request
    to modify an existing entry to note the separate use.
 o  Contact information identifying the person supplying the
    registration must be included.  Previously unregistered schemes
    discovered in use can be registered by third parties (even if not
    on behalf of those who created the scheme).  In this case, both
    the registering party and the scheme creator SHOULD be identified.
 o  If no permanent, citable specification for the scheme definition
    is included, credible reasons for not providing it SHOULD be
    given.
 o  The scheme definition SHOULD include clear security considerations
    (Section 3.7) or explain why a full security analysis is not
    available (e.g., in a third-party scheme registration).
 o  If the scheme definition does not meet the guidelines laid out in
    Section 3, the differences and reasons SHOULD be noted.

Thaler, et al. Best Current Practice [Page 9] RFC 7595 URI Scheme Guidelines June 2015

5. Guidelines for Historical URI Scheme Registration

 In some circumstances, it is appropriate to note a scheme that was
 once in use or registered but for whatever reason is no longer in
 common use or whose use is not recommended.  In this case, it is
 possible for an individual to request that the URI scheme be
 registered (newly, or as an update to an existing registration) as
 'historical'.  Any scheme that is no longer in common use MAY be
 designated as 'historical'; the registration SHOULD contain some
 indication as to where the scheme was previously defined or
 documented.

6. Guidelines for Private URI Scheme Use

 Unregistered schemes can cause problems if use is not limited to a
 private environment within a single organization since the use could
 leak out beyond the closed environment.  Even within a closed
 environment, other colliding uses of the same scheme name could
 occur.  As such, a unique namespace MUST be used and 'provisional'
 registration is strongly encouraged (unless the scheme name is
 constructed from a domain name), as discussed in Section 3.8.

7. URI Scheme Registration Procedure

7.1. General

 The IANA policy (using terms defined in [RFC5226]) for 'provisional'
 registration was formerly Expert Review; this document changes the
 policy to First Come First Served.  The policy for 'permanent' and
 'historical' registration continues to be Expert Review.
 The registration procedure is intended to be very lightweight for
 noncontentious registrations.  For the most part, we expect the good
 sense of submitters and reviewers, guided by these procedures, to
 achieve an acceptable and useful consensus for the community.
 In exceptional cases, where the negotiating parties cannot form a
 consensus, the final arbiter of any contested registration shall be
 the IESG.
 If standardization is anticipated, the working group or individuals
 concerned are advised to submit an early 'permanent' registration
 request rather than waiting until the standardization process has run
 its course.  IANA will pass this to the Designated Expert who may
 recommend 'provisional' registration until the specification is
 approved as a standard.  This will provide an opportunity for
 feedback while specification development and review is still active,
 and while the submitter(s) are still in a position to respond to any

Thaler, et al. Best Current Practice [Page 10] RFC 7595 URI Scheme Guidelines June 2015

 issues that might be raised.  If and when the specification is
 approved as a standard, the submitters should submit a request to
 change the registration status to 'permanent'.
 The role of the Designated Expert in the procedure for 'permanent'
 registrations described here is to ensure that the normal open review
 process has been properly followed and to raise possible concerns
 about wider implications of proposals for the use and deployment of
 URIs.  Nothing in the procedure empowers the Designated Expert to
 override properly arrived-at IETF or working group consensus.

7.2. Registration Procedures

 Someone wishing to register a new scheme MUST:
 1.  Check the IANA "Uniform Resource Identifier (URI) Schemes"
     registry to see whether there is already an entry for the desired
     name.  If there is already an entry under the name, choose a
     different scheme name or update the existing scheme
     specification.
 2.  Prepare a scheme registration request using the template
     specified in Section 7.4.  The scheme registration request can be
     contained in an Internet-Draft, submitted alone, or as part of
     some other permanently available, stable, protocol specification.
     The scheme registration request can also be submitted in some
     other form (as part of another document or as a stand-alone
     document), but the scheme registration request will be treated as
     an "IETF Contribution" under the guidelines of [RFC5378].
 3.  If the registration request is for a 'permanent' registration
     (or, optionally, for any other registration if desired):
     1.  Review the requirements in Section 3.
     2.  Send a copy of the scheme registration request or a pointer
         to the document containing the request (with specific
         reference to the section that requests the scheme
         registration) to the mailing list uri-review@ietf.org,
         requesting review.  In addition, request review on other
         relevant mailing lists as appropriate.  For example, general
         discussion of URI syntactical issues can be discussed on
         uri@w3.org; schemes for a network protocol can be discussed
         on a mailing list for that protocol.  Allow a reasonable time
         for discussion and comments.  Four weeks is reasonable for a
         'permanent' registration request.

Thaler, et al. Best Current Practice [Page 11] RFC 7595 URI Scheme Guidelines June 2015

     3.  Respond to review comments and make revisions to the proposed
         registration as needed to bring it into line with the
         guidelines given in this document.
 4.  Submit the (possibly updated) scheme registration request (or
     pointer to document containing it) to IANA at iana@iana.org.
 Upon receipt of a scheme registration request, the following steps
 MUST be followed:
 1.  IANA checks the submission for completeness; if required sections
     of the scheme registration request are missing or any citations
     are not correct, IANA will reject the registration request.  A
     registrant can resubmit a corrected request if desired.
 2.  If the request is for 'provisional' registration and no entry
     already exists in the current registry for the same name, IANA
     adds the registration to the registry under the First Come First
     Served policy.
 3.  Otherwise, IANA enters the registration request in the IANA
     registry with the status marked as "Pending Review", and the
     remainder of this section applies.
 4.  IANA requests Expert Review of the registration request against
     the corresponding guidelines from this document.
 5.  The Designated Expert will evaluate the request against the
     criteria of the requested status.
 6.  In the case of a 'permanent' registration request, the Designated
     Expert may:
  • Accept the specification of the scheme for 'permanent'

registration.

  • Suggest 'provisional' registration instead.
  • Request IETF review and IESG approval; in the meanwhile,

suggest 'provisional' registration.

  • Request additional review or discussion as necessary.
 7.  If an entry already exists for the same name, the Designated
     Expert will determine whether the request should be rejected or
     whether the existing entry should be modified to note the
     separate use.  This conflict process applies regardless of the
     requested status or the status of the existing entry.

Thaler, et al. Best Current Practice [Page 12] RFC 7595 URI Scheme Guidelines June 2015

 8.  Once the Designated Expert approves registration for a given
     status, IANA updates the registration to indicate the approved
     status.  If the Designated Expert instead rejects the
     registration, the "Pending Review" request is removed from the
     registry.
 Either based on an explicit request or independently initiated, the
 Designated Expert or the IESG can request the upgrade of a
 'provisional' registration to a 'permanent' one.  In such cases, IANA
 will update the status of the corresponding entry.  Typically, this
 would only occur if the use is considered a standard (not necessarily
 an IETF standard).

7.3. Change Control

 Registrations can be updated in the registry by the same mechanism as
 required for an initial registration.  In cases where the original
 definition of the scheme is contained in an IESG-approved document,
 update of the specification also requires IESG approval.
 'Provisional' registrations can be updated by the original registrant
 or anyone designated by the original registrant.  In addition, the
 IESG can reassign responsibility for a 'provisional' registration
 scheme or can request specific changes to a scheme registration.
 This will enable changes to be made to schemes where the original
 registrant is out of contact or unwilling or unable to make changes.
 Transition from 'provisional' to 'permanent' status can be requested
 and approved in the same manner as a new 'permanent' registration.
 Transition from 'permanent' to 'historical' status requires IESG
 approval.  Transition from 'provisional' to 'historical' can be
 requested by anyone authorized to update the 'provisional'
 registration.

7.4. URI Scheme Registration Template

 This template describes the fields that MUST be supplied in a scheme
 registration request suitable for adding to the registry:
 Scheme name:
   See Section 3.8 for guidelines.
 Status:
   This reflects the status requested and must be one of 'Permanent',
   'Provisional', or 'Historical'.
 Applications/protocols that use this scheme name:
   See Section 3.5.

Thaler, et al. Best Current Practice [Page 13] RFC 7595 URI Scheme Guidelines June 2015

 Contact:
   Person (including contact information) to contact for further
   information.
 Change controller:
   Organization or person (often the author), including contact
   information, authorized to change this.
 References:
   Include full citations for all referenced documents.  Scheme
   registration requests for 'provisional' registration can be
   included in an Internet-Draft; when the documents expire or are
   approved for publication as an RFC, the registration will be
   updated.  A scheme specification is only required for 'permanent'
   registration.
 The previous version of this specification required the following
 additional fields in a scheme registration request.  These fields are
 no longer part of the template.  The answers instead belong in the
 scheme specification.
 Scheme syntax:
   See Section 3.2 for guidelines.
 Scheme semantics:
   See Section 3.3 and Section 3.4 for guidelines.
 Encoding considerations:
   See Section 3.3 and Section 3.6 for guidelines.
 Interoperability considerations:
   See Section 3.9 for guidelines.
 Security considerations:
   See Section 3.7 for guidelines.

8. The "example" URI Scheme

 There is a need for a scheme name that can be used for examples in
 documentation without fear of conflicts with current or future actual
 schemes.  The scheme "example" is hereby registered as a 'permanent'
 scheme for that purpose.

Thaler, et al. Best Current Practice [Page 14] RFC 7595 URI Scheme Guidelines June 2015

 The "example" scheme is specified as follows:
 Scheme syntax:  The entire range of allowable syntax specified in
   [RFC3986] is allowed for "example" URIs.  Similarly, the entire
   range of allowable syntax specified in [RFC3987] is allowed for
   "example" IRIs.  For example, <example:foo>, <example:/foo>, and
   <example://foo> are all valid.
 Scheme semantics:  URIs in the "example" scheme are to be used for
   documentation purposes only.  The use of "example" URIs must not be
   used as locators, identify any resources, or specify any particular
   set of operations.
 Encoding considerations:  See Section 2.5 of [RFC3986] for
   guidelines.
 Interoperability considerations:  None.
 Security considerations:  None.

8.1. "example" URI Scheme Registration Request

 Scheme name:  example
 Status:  permanent
 Applications/protocols that use this scheme name:  An "example" URI
   is to be used for documentation purposes only.  It MUST NOT be used
   for any protocol.
 Contact:  N/A
 Change controller:  IETF
 References:  Section 8 of this document (RFC 7595).

9. IANA Considerations

 Previously, the former "URL Scheme" registry was replaced by the
 "Uniform Resource Identifier (URI) Schemes" registry.  The process
 was based on "Expert Review" [RFC5226] with an initial (optional)
 mailing list review.
 The updated template has an additional field for the status of the
 scheme, and the procedures for entering new name schemes have been
 augmented.  Section 7 establishes the process for new scheme
 registration.

Thaler, et al. Best Current Practice [Page 15] RFC 7595 URI Scheme Guidelines June 2015

 IANA has done the following:
 o  Updated the URI Schemes registry to point to this document.
 o  Combined the "Permanent URI Schemes", "Provisional URI Schemes",
    and "Historical URI Schemes" subregistries into a single common
    registry with an additional "Status" column containing the status
    ('Permanent', 'Provisional', 'Historical', or 'Pending Review'),
    and an additional "Notes" column that is normally empty but may
    contain notes approved by the Designated Expert.
 o  Added the "example" URI scheme to the registry (see the template
    in Section 8.1 for registration).

10. Security Considerations

 All registered values are expected to contain clear security
 considerations as discussed in Section 3.7.  However, information
 concerning possible security vulnerabilities of a protocol might
 change over time.  Consequently, claims as to the security properties
 of a registered scheme might change as well.  As new vulnerabilities
 are discovered, information about such vulnerabilities might need to
 be attached to existing documentation, so that users are not misled
 as to the true security properties of a registered scheme.

11. References

11.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2141]  Moats, R., "URN Syntax", RFC 2141, DOI 10.17487/RFC2141,
            May 1997, <http://www.rfc-editor.org/info/rfc2141>.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66,
            RFC 3986, DOI 10.17487/RFC3986, January 2005,
            <http://www.rfc-editor.org/info/rfc3986>.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.

Thaler, et al. Best Current Practice [Page 16] RFC 7595 URI Scheme Guidelines June 2015

 [RFC5378]  Bradner, S., Ed. and J. Contreras, Ed., "Rights
            Contributors Provide to the IETF Trust", BCP 78, RFC 5378,
            DOI 10.17487/RFC5378, November 2008,
            <http://www.rfc-editor.org/info/rfc5378>.
 [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
            Cheshire, "Internet Assigned Numbers Authority (IANA)
            Procedures for the Management of the Service Name and
            Transport Protocol Port Number Registry", BCP 165,
            RFC 6335, DOI 10.17487/RFC6335, August 2011,
            <http://www.rfc-editor.org/info/rfc6335>.

11.2. Informative References

 [RFC2717]  Petke, R. and I. King, "Registration Procedures for URL
            Scheme Names", RFC 2717, DOI 10.17487/RFC2717, November
            1999, <http://www.rfc-editor.org/info/rfc2717>.
 [RFC2718]  Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
            "Guidelines for new URL Schemes", RFC 2718,
            DOI 10.17487/RFC2718, November 1999,
            <http://www.rfc-editor.org/info/rfc2718>.
 [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
            "Uniform Resource Names (URN) Namespace Definition
            Mechanisms", BCP 66, RFC 3406, DOI 10.17487/RFC3406,
            October 2002, <http://www.rfc-editor.org/info/rfc3406>.
 [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
            Procedures for Message Header Fields", BCP 90, RFC 3864,
            DOI 10.17487/RFC3864, September 2004,
            <http://www.rfc-editor.org/info/rfc3864>.
 [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
            Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
            January 2005, <http://www.rfc-editor.org/info/rfc3987>.
 [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
            Registration Procedures for New URI Schemes", RFC 4395,
            DOI 10.17487/RFC4395, February 2006,
            <http://www.rfc-editor.org/info/rfc4395>.
 [RFC4690]  Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
            Recommendations for Internationalized Domain Names
            (IDNs)", RFC 4690, DOI 10.17487/RFC4690, September 2006,
            <http://www.rfc-editor.org/info/rfc4690>.

Thaler, et al. Best Current Practice [Page 17] RFC 7595 URI Scheme Guidelines June 2015

 [W3CWebArch]
            W3C Technical Architecture Group, "Architecture of the
            World Wide Web, Volume One", W3C Recommendation, December
            2004, <http://www.w3.org/TR/webarch/>.

Acknowledgements

 Thanks to Mark Nottingham and Graham Klyne and other members of the
 apps-discuss@ietf.org mailing list for their comments on this
 document.
 Many thanks to Patrik Faltstrom, Paul Hoffmann, Ira McDonald, Roy
 Fielding, Stu Weibel, Tony Hammond, Charles Lindsey, Mark Baker, and
 other members of the uri@w3.org mailing list for their comments on
 earlier draft versions of this document.
 Parts of this document are based on [RFC2717], [RFC2718] and
 [RFC3864].  Some of the ideas about use of URIs were taken from the
 "Architecture of the World Wide Web" [W3CWebArch].

Contributor

 Larry Masinter was an author of the document from which this work is
 derived, and he continued as author of this version through the
 working group and IESG evaluation period.  His many contributions are
 gratefully acknowledged.

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Authors' Addresses

 Dave Thaler (editor)
 Microsoft
 One Microsoft Way
 Redmond, WA  98052
 United States
 Phone: +1 425 703 8835
 EMail: dthaler@microsoft.com
 Tony Hansen
 AT&T Laboratories
 200 Laurel Ave.
 Middletown, NJ  07748
 United States
 EMail: tony+urireg@maillennium.att.com
 Ted Hardie
 Google
 Phone: +1 408 628 5864
 EMail: ted.ietf@gmail.com

Thaler, et al. Best Current Practice [Page 19]

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