rfc2978.txt

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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.

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].






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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].






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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





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   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.



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   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-
   [e-mail]" 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




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   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.