Network Working Group Ned Freed, Innosoft
Internet Draft Jon Postel, ISI
Obsoletes: 2278 <draft-freed-charset-regist-02.txt>
IANA Charset
Registration Procedures
May 2000
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC 2026.
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Copyright Notice
Copyright (C) The Internet Society (2000). All Rights
Reserved.
1. Abstract
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.
Internet Draft Charset Registration May 2000
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.
2. Definitions and Notation
The following sections define terms used in this document.
2.1. 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].
2.2. Character
A member of a set of elements used for the organisation,
control, or representation of data.
2.3. 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.
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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, to be used as charsets.
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.
2.4. 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].
2.5. 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 typically associated with a
single CCS; for example, UTF-8 applies only to ISO 10646.
3. Charset Registration Requirements
Registered charsets are expected to conform to a number of
requirements as described below.
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3.1. 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 a CCS
and a CES MUST either include the CCS and CES they are based
on in their registration or else cite a definition of their
CCS 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.
3.2. 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 mechanisims 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.
3.3. 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 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
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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
3.4. 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.
3.5. 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 unlabelled charsets hampers
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interoperability even more.
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.
3.6. 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.
3.7. 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.
4. 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
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intended to allow community comment and sanity checking
without excessive time delay.
4.1. 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 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 intent of the public posting is to solicit comments and
feedback on the definition of the charset and the name chosen
for it over a two week period.
4.2. 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.
Decisions made by the reviewer must be posted to the ietf-
charsets mailing list within 14 days. Decisions made by the
reviewer may be appealed to the IESG.
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4.3. 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.
5. 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]).
6. 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 a CCS and a CES then these defintions
MUST either be included or referenced.)
ISO 10646 equivalency table:
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(A URL 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)
7. 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.
8. 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.
9. IANA Actions
(THIS SECTION SHOULD BE REMOVED BEFORE PUBLICATION.) The IANA
Web site needs to be updated with information about the ietf-
charsets mailing list. In particular, it needs to specify the
list address (ietf-charsets@iana.org), the subscription
address (ietf-charsets-request@iana.org), the subscription
methodology (send a message with one line in the body saying
"SUBSCRIBE IETF-CHARSETS"), and the location of the list
archives (currently ftp://ftp.innosoft.com/ietf-charsets, but
likely to change in the near future).
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10. 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 8859-1:1987, 1st ed.
- Part 2: Latin Alphabet No. 2, ISO 8859-2:1987, 1st ed.
- Part 3: Latin Alphabet No. 3, ISO 8859-3:1988, 1st ed.
- Part 4: Latin Alphabet No. 4, ISO 8859-4:1988, 1st ed.
- Part 5: Latin/Cyrillic Alphabet, ISO 8859-5:1988, 1st
ed.
- Part 6: Latin/Arabic Alphabet, ISO 8859-6:1987, 1st ed.
- Part 7: Latin/Greek Alphabet, ISO 8859-7:1987, 1st ed.
- Part 8: Latin/Hebrew Alphabet, ISO 8859-8:1988, 1st ed.
- Part 9: Latin Alphabet No. 5, ISO/IEC 8859-9:1989, 1st
ed.
International Standard -- Information Technology -- 8-bit
Single-Byte Coded Graphic Character Sets
- Part 10: Latin Alphabet No. 6, ISO/IEC 8859-10:1992,
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.
[RFC-1590]
Postel, J., "Media Type Registration Procedure", RFC
1590, USC/Information Sciences Institute, March 1994.
[RFC-1700]
Reynolds, J. and Postel, J., "Assigned Numbers", STD 2,
RFC 1700, USC/Information Sciences Institute, October
1994.
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[RFC-1759]
Smith, R., Wright, F., Hastings, T., Zilles, S.,
Gyllenskog, J., "Printer MIB", RFC 1759, March 1995.
[RFC-2045]
Freed, N. and Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, Bellcore, Innosoft, November 1996.
[RFC-2046]
Freed, N. and Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
Bellcore, Innosoft, November 1996.
[RFC-2047]
Moore, K., "Multipurpose Internet Mail Extensions (MIME)
Part Three: Representation of Non-Ascii Text in Internet
Message Headers", RFC 2047, University of Tennessee,
November 1996.
[RFC-2119]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC-2130]
Weider, C., Preston, C., Simonsen, K., Alvestrand, H.,
Atkinson, R., Crispin, M., Svanberg, P., "Report from the
IAB Character Set Workshop", RFC 2130, April 1997.
[RFC-2184]
Freed, N., Moore, K., "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., Postel, J., "IANA Charset Registration
Procedures", RFC 2278, January 1998.
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[US-ASCII]
Coded Character Set -- 7-Bit American Standard Code for
Information Interchange, ANSI X3.4-1986.
11. Authors' Addresses
Ned Freed
Innosoft International, Inc. 1050 Lakes Drive West Covina, CA
91790 USA
tel: +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.
12. 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.
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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.
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