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Obsoletes:
Keywords: character, set, mime, multipurpose, internet, mail, extensions
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.
Abstract
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
characters.
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
text.
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
contexts.
Charset registrations SHOULD include a specification of mapping from
the charset into ISO 10646 if specification of such a mapping is
feasible.
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-
charsets@iana.org" mailing list. (Information about joining this
list is available on the IANA Website, http://www.iana.org.) 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
"ftp://ftp.isi.edu/in-notes/iana/assignments/character-sets" 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 "rfc-editor@isi.edu" (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
To: ietf-charsets@iana.org
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
provided.)
Additional information:
Person & email address to contact for further information:
Intended usage:
(One of COMMON, LIMITED USE or OBSOLETE)
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
[ISO-2022]
International Standard -- Information Processing --
Character Code Structure and Extension Techniques,
ISO/IEC 2022:1994, 4th ed.
[ISO-8859]
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-10646]
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
EMail: ned.freed@innosoft.com
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
English.
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
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Freed & Postel Best Current Practice [Page 11]