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Network Working Group N. Freed Request for Comments: 2978 Innosoft BCP: 19 J. Postel Obsoletes: 2278 ISI Category: Best Current Practice October 2000

                IANA Charset Registration Procedures

Status of this Memo

 This document specifies an Internet Best Current Practices for the
 Internet Community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.


 Multipurpose Internet Mail Extensions (MIME) (RFC-2045, RFC-2046,
 RFC-2047, RFC-2184) and various other Internet protocols are capable
 of using many different charsets.  This in turn means that the
 ability to label different charsets is essential.
 Note: The charset registration procedure exists solely to associate a
 specific name or names with a given charset and to give an indication
 of whether or not a given charset can be used in MIME text objects.
 In particular, the general applicability and appropriateness of a
 given registered charset to a particular application is a protocol
 issue, not a registration issue, and is not dealt with by this
 registration procedure.

1. Definitions and Notation

 The following sections define terms used in this document.

1.1. Requirements Notation

 This document occasionally uses terms that appear in capital letters.
 When the terms "MUST", "SHOULD", "MUST NOT", "SHOULD NOT", and "MAY"
 appear capitalized, they are being used to indicate particular
 requirements of this specification.  A discussion of the meanings of
 these terms appears in [RFC-2119].

Freed & Postel Best Current Practice [Page 1] RFC 2978 IANA Charset Registration Procedures October 2000

1.2. Character

 A member of a set of elements used for the organization, control, or
 representation of data.

1.3. Charset

 The term "charset" (referred to as a "character set" in previous
 versions of this document) is used here to refer to a method of
 converting a sequence of octets into a sequence of characters.  This
 conversion may also optionally produce additional control information
 such as directionality indicators.
 Note that unconditional and unambiguous conversion in the other
 direction is not required, in that not all characters may be
 representable by a given charset and a charset may provide more than
 one sequence of octets to represent a particular sequence of
 This definition is intended to allow charsets to be defined in a
 variety of different ways, from simple single-table mappings such as
 US-ASCII to complex table switching methods such as those that use
 ISO 2022's techniques.  However, the definition associated with a
 charset name must fully specify the mapping to be performed.  In
 particular, use of external profiling information to determine the
 exact mapping is not permitted.
 HISTORICAL NOTE: The term "character set" was originally used in MIME
 to describe such straightforward schemes as US-ASCII and ISO-8859-1
 which consist of a small set of characters and a simple one-to-one
 mapping from single octets to single characters.  Multi-octet
 character encoding schemes and switching techniques make the
 situation much more complex.  As such, the definition of this term
 was revised to emphasize both the conversion aspect of the process,
 and the term itself has been changed to "charset" to emphasize that
 it is not, after all, just a set of characters.  A discussion of
 these issues as well as specification of standard terminology for use
 in the IETF appears in RFC 2130.

1.4. Coded Character Set

 A Coded Character Set (CCS) is a one-to-one mapping from a set of
 abstract characters to a set of integers.  Examples of coded
 character sets are ISO 10646 [ISO-10646], US-ASCII [US-ASCII], and
 the ISO-8859 series [ISO-8859].

Freed & Postel Best Current Practice [Page 2] RFC 2978 IANA Charset Registration Procedures October 2000

1.5. Character Encoding Scheme

 A Character Encoding Scheme (CES) is a mapping from a Coded Character
 Set or several coded character sets to a set of octet sequences.  A
 given CES is sometimes associated with a single CCS; for example,
 UTF-8 applies only to ISO 10646.

2. Charset Registration Requirements

 Registered charsets are expected to conform to a number of
 requirements as described below.

2.1. Required Characteristics

 Registered charsets MUST conform to the definition of a "charset"
 given above.  In addition, charsets intended for use in MIME content
 types under the "text" top-level type MUST conform to the
 restrictions on that type described in RFC 2045.  All registered
 charsets MUST note whether or not they are suitable for use in MIME
 All charsets which are constructed as a composition of one or more
 CCS's and a CES MUST either include the CCS's and CES they are based
 on in their registration or else cite a definition of their CCS's and
 CES that appears elsewhere.
 All registered charsets MUST be specified in a stable, openly
 available specification.  Registration of charsets whose
 specifications aren't stable and openly available is forbidden.

2.2. New Charsets

 This registration mechanism is not intended to be a vehicle for the
 design and definition of entirely new charsets.  This is due to the
 fact that the registration process does NOT contain adequate review
 mechanisms for such undertakings.
 As such, only charsets defined by other processes and standards
 bodies, or specific profiles or combinations of such charsets, are
 eligible for registration.

2.3. Naming Requirements

 One or more names MUST be assigned to all registered charsets.
 Multiple names for the same charset are permitted, but if multiple
 names are assigned a single primary name for the charset MUST be

Freed & Postel Best Current Practice [Page 3] RFC 2978 IANA Charset Registration Procedures October 2000

 identified. All other names are considered to be aliases for the
 primary name and use of the primary name is preferred over use of any
 of the aliases.
 Each assigned name MUST uniquely identify a single charset.  All
 charset names MUST be suitable for use as the value of a MIME content
 type charset parameter and hence MUST conform to MIME parameter value
 syntax.  This applies even if the specific charset being registered
 is not suitable for use with the "text" media type.
 All charsets MUST be assigned a name that provides a display string
 for the associated "MIBenum" value defined below.  These "MIBenum"
 values are defined by and used in the Printer MIB [RFC-1759].  Such
 names MUST begin with the letters "cs" and MUST contain no more than
 40 characters (including the "cs" prefix) chosen from from the
 printable subset of US-ASCII.  Only one name beginning with "cs" may
 be assigned to a single charset.  If no name of this form is
 explicitly defined IANA will assign an alias consisting of "cs"
 prepended to the primary charset name.
 Finally, charsets being registered for use with the "text" media type
 MUST have a primary name that conforms to the more restrictive syntax
 of the charset field in MIME encoded-words [RFC-2047, RFC-2184] and
 MIME extended parameter values [RFC-2184].  A combined ABNF
 definition for such names is as follows:
   mime-charset = 1*mime-charset-chars
   mime-charset-chars = ALPHA / DIGIT /
              "!" / "#" / "$" / "%" / "&" /
              "'" / "+" / "-" / "^" / "_" /
              "`" / "{" / "}" / "~"
   ALPHA        = "A".."Z"    ; Case insensitive ASCII Letter
   DIGIT        = "0".."9"    ; Numeric digit

2.4. Functionality Requirement

 Charsets MUST function as actual charsets: Registration of things
 that are better thought of as a transfer encoding, as a media type,
 or as a collection of separate entities of another type, is not
 allowed.  For example, although HTML could theoretically be thought
 of as a charset, it is really better thought of as a media type and
 as such it cannot be registered as a charset.

2.5. Usage and Implementation Requirements

 Use of a large number of charsets in a given protocol may hamper
 interoperability.  However, the use of a large number of undocumented
 and/or unlabeled charsets hampers interoperability even more.

Freed & Postel Best Current Practice [Page 4] RFC 2978 IANA Charset Registration Procedures October 2000

 A charset should therefore be registered ONLY if it adds significant
 functionality that is valuable to a large community, OR if it
 documents existing practice in a large community.  Note that charsets
 registered for the second reason should be explicitly marked as being
 of limited or specialized use and should only be used in Internet
 messages with prior bilateral agreement.

2.6. Publication Requirements

 Charset registrations MAY be published in RFCs, however, RFC
 publication is not required to register a new charset.
 The registration of a charset does not imply endorsement, approval,
 or recommendation by the IANA, IESG, or IETF, or even certification
 that the specification is adequate.  It is expected that
 applicability statements for particular applications will be
 published from time to time that recommend implementation of, and
 support for, charsets that have proven particularly useful in those
 Charset registrations SHOULD include a specification of mapping from
 the charset into ISO 10646 if specification of such a mapping is

2.7. MIBenum Requirements

 Each registered charset MUST also be assigned a unique enumerated
 integer value.  These "MIBenum" values are defined by and used in the
 Printer MIB [RFC-1759].
 A MIBenum value for each charset will be assigned by IANA at the time
 of registration.  MIBenum values are not assigned by the person
 registering the charset.

3. Charset Registration Procedure

 The following procedure has been implemented by the IANA for review
 and approval of new charsets.  This is not a formal standards
 process, but rather an administrative procedure intended to allow
 community comment and sanity checking without excessive time delay.

3.1. Present the Charset to the Community

 Send the proposed charset registration to the "ietf-" mailing list.  (Information about joining this
 list is available on the IANA Website,  This
 mailing list has been established for the sole purpose of reviewing

Freed & Postel Best Current Practice [Page 5] RFC 2978 IANA Charset Registration Procedures October 2000

 proposed charset registrations. Proposed charsets are not formally
 registered and must not be used; the "x-" prefix specified in RFC
 2045 can be used until registration is complete.
 The posting of a charset to the list initiates a two week public
 review process.
 The intent of the public posting is to solicit comments and feedback
 on the definition of the charset and the name chosen for it.

3.2. Charset Reviewer

 When the two week period has passed and the registration proposer is
 convinced that consensus has been achieved, the registration
 application should be submitted to IANA and the charset reviewer.
 The charset reviewer, who is appointed by the IETF Applications Area
 Director(s), either approves the request for registration or rejects
 it.  Rejection may occur because of significant objections raised on
 the list or objections raised externally.  If the charset reviewer
 considers the registration sufficiently important and controversial,
 a last call for comments may be issued to the full IETF.  The charset
 reviewer may also recommend standards track processing (before or
 after registration) when that appears appropriate and the level of
 specification of the charset is adequate.
 The charset reviewer must reach a decision and post it to the ietf-
 charsets mailing list within two weeks.  Decisions made by the
 reviewer may be appealed to the IESG.

3.3. IANA Registration

 Provided that the charset registration has either passed review or
 has been successfully appealed to the IESG, the IANA will register
 the charset, assign a MIBenum value, and make its registration
 available to the community.

4. Location of Registered Charset List

 Charset registrations will be posted in the anonymous FTP file
 "" and all
 registered charsets will be listed in the periodically issued
 "Assigned Numbers" RFC [currently RFC-1700].  The description of the
 charset MAY also be published as an Informational RFC by sending it
 to "" (please follow the instructions to RFC
 authors [RFC-1543]).

Freed & Postel Best Current Practice [Page 6] RFC 2978 IANA Charset Registration Procedures October 2000

5. Charset Registration Template

   Subject: Registration of new charset [names]
   Charset name:
   (All names must be suitable for use as the value of a
   MIME content-type parameter.)
   Charset aliases:
   (All aliases must also be suitable for use as the value of
   a MIME content-type parameter.)
   Suitability for use in MIME text:
   Published specification(s):
   (A specification for the charset MUST be
   openly available that accurately describes what
   is being registered. If a charset is defined as
   a composition of one or more CCS's and a CES then these
   definitions MUST either be included or referenced.)
   ISO 10646 equivalency table:
   (A URI to a specification of how to translate from
   this charset to ISO 10646 and vice versa SHOULD be
   Additional information:
   Person & email address to contact for further information:
   Intended usage:

6. Security Considerations

 This registration procedure is not known to raise any sort of
 security considerations that are appreciably different from those
 already existing in the protocols that employ registered charsets.

Freed & Postel Best Current Practice [Page 7] RFC 2978 IANA Charset Registration Procedures October 2000

7. Changes made since RFC 2278

 Inclusion of a mapping to ISO 10646 is now recommended for all
 registered charsets.  The registration template has been updated to
 include this as well as a place to indicate whether or not the
 charset is suitable for use in MIME text.

8. References

       International Standard -- Information Processing --
       Character Code Structure and Extension Techniques,
       ISO/IEC 2022:1994, 4th ed.
       International Standard -- Information Processing -- 8-bit
       Single-Byte Coded Graphic Character Sets
       - Part 1: Latin Alphabet No. 1, ISO 8859-1:1998, 1st ed.
       - Part 2: Latin Alphabet No. 2, ISO 8859-2:1999, 1st ed.
       - Part 3: Latin Alphabet No. 3, ISO 8859-3:1999, 1st ed.
       - Part 4: Latin Alphabet No. 4, ISO 8859-4:1998, 1st ed.
       - Part 5: Latin/Cyrillic Alphabet, ISO 8859-5:1999, 2nd ed.
       - Part 6: Latin/Arabic Alphabet, ISO 8859-6:1999, 1st ed.
       - Part 7: Latin/Greek Alphabet, ISO 8859-7:1987, 1st ed.
       - Part 8: Latin/Hebrew Alphabet, ISO 8859-8:1999, 1st ed.
       - Part 9: Latin Alphabet No. 5, ISO/IEC 8859-9:1999, 2nd ed.
       International Standard -- Information Technology -- 8-bit
       Single-Byte Coded Graphic Character Sets
       - Part 10: Latin Alphabet No. 6, ISO/IEC 8859-10:1998, 2nd ed.
       International Standard -- Information Technology -- 8-bit
       Single-Byte Coded Graphic Character Sets
       - Part 13: Latin Alphabet No. 7, ISO/IEC 8859-10:1998, 1st ed.
       International Standard -- Information Technology -- 8-bit
       Single-Byte Coded Graphic Character Sets
       - Part 14: Latin Alphabet No. 8 (Celtic), ISO/IEC
       8859-10:1998, 1st ed.
       International Standard -- Information Technology -- 8-bit
       Single-Byte Coded Graphic Character Sets
       - Part 15: Latin Alphabet No. 9, ISO/IEC 8859-10:1999,
       1st ed.
       ISO/IEC 10646-1:1993(E),  "Information technology --
       Universal Multiple-Octet Coded Character Set (UCS) --
       Part 1: Architecture and Basic Multilingual Plane",
       JTC1/SC2, 1993.

Freed & Postel Best Current Practice [Page 8] RFC 2978 IANA Charset Registration Procedures October 2000

 [RFC-1590] Postel, J., "Media Type Registration Procedure", RFC
            1590,March 1994.
 [RFC-1700] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC
            1700, October 1994.
 [RFC-1759] Smith, R., Wright, F., Hastings, T., Zilles, S. and J.
            Gyllenskog, "Printer MIB", RFC 1759, March 1995.
 [RFC-2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part One: Format of Internet Message
            Bodies", RFC 2045, November 1996.
 [RFC-2046] Freed, N. and  N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part Two: Media Types", RFC 2046,
            November 1996.
 [RFC-2047] Moore, K., "Multipurpose Internet Mail Extensions (MIME)
            Part Three: Representation of Non-Ascii Text in Internet
            Message Headers", RFC 2047, November 1996.
 [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC-2130] Weider, C., Preston, C., Simonsen, K., Alvestrand, H.,
            Atkinson, R., Crispin, M. and P. Svanberg, "Report from
            the IAB Character Set Workshop", RFC 2130, April 1997.
 [RFC-2184] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
            Word Extensions: Character Sets, Languages, and
            Continuations", RFC 2184, August 1997.
 [RFC-2468] Cerf, V., "I Remember IANA", RFC 2468, October 1998.
 [RFC-2278] Freed, N. and J. Postel, "IANA Charset Registration
            Procedures", BCP 19, RFC 2278, January 1998.
 [US-ASCII] Coded Character Set -- 7-Bit American Standard Code for
            Information Interchange, ANSI X3.4-1986.

Freed & Postel Best Current Practice [Page 9] RFC 2978 IANA Charset Registration Procedures October 2000

10. Authors' Addresses

 Ned Freed
 Innosoft International, Inc.
 1050 Lakes Drive
 West Covina, CA 91790 USA
 Phone: +1 626 919 3600
 Fax: +1 626 919 3614
 Jon Postel
 Sadly, Jon Postel, the co-author of this document, passed away on
 October 16, 1998 [RFC-2468].  Any omissions or errors are solely the
 responsibility of the remaining co-author.

Freed & Postel Best Current Practice [Page 10] RFC 2978 IANA Charset Registration Procedures October 2000

11. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an


 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Freed & Postel Best Current Practice [Page 11]

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