rfc2278.txt

来自「RFC 的详细文档！」· 文本 代码 · 共 564 行 · 第 1/2 页

Network Working Group                                           N. Freed
Request for Comments: 2278                                      Innosoft
BCP: 19                                                        J. Postel
Category: Best Current Practice                                      ISI
                                                            January 1998

                              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 (1998).  All Rights Reserved.

1.  Abstract

   MIME [RFC-2045, RFC-2046, RFC-2047, RFC-2184] and various other
   modern Internet protocols are capable of using many different
   charsets. This in turn means that the ability to label different
   charsets is essential. This 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 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 various 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].








Freed & Postel           Best Current Practice                  [Page 1]

RFC 2278                  Charset Registration              January 1998


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" (see historical note below) 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, 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 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 2278                  Charset Registration              January 1998


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 octets. A given CES
   is typically associated with a single CCS; for example, UTF-8 applies
   only to ISO 10646.

3.  Registration Requirements

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

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.

   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
   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 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.



Freed & Postel           Best Current Practice                  [Page 3]

RFC 2278                  Charset Registration              January 1998


   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.

   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*<Any CHAR except SPACE, CTLs, and cspecials>

   cspecials    = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "
                  <"> / "/" / "[" / "]" / "?" / "." / "=" / "*"

   CHAR         =  <any ASCII character>        ; (  0-177,  0.-127.)
   SPACE        =  <ASCII SP, space>            ; (     40,      32.)
   CTL          =  <any ASCII control           ; (  0- 37,  0.- 31.)
                    character and DEL>          ; (    177,     127.)

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 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 can be published in RFCs, however, RFC
   publication is not required to register a new charset.



Freed & Postel           Best Current Practice                  [Page 4]

RFC 2278                  Charset Registration              January 1998


   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.

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.

4.  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.

4.1.  Present the Charset to the Community

   Send the proposed charset registration to the "ietf-
   [e-mail]" mailing list.  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




Freed & Postel           Best Current Practice                  [Page 5]