From: http://www.ietf.org/internet-drafts/draft-phillips-langtags-04.txt
Title: Tags for Identifying Languages
Reference: IETF Network Working Group, Internet Draft, 'draft-phillips-langtags-04'
Date: June 24, 2004
========================================================================
Network Working Group A. Phillips, Ed.
Internet-Draft webMethods, Inc.
Expires: December 23, 2004 M. Davis
IBM
June 24, 2004
Tags for Identifying Languages
draft-phillips-langtags-04
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on December 23, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes the structure, content, construction, and
semantics of language tags for use in cases where it is desirable to
indicate the language used in an information object. It also
describes how to register values for use in language tags and a
construct for matching such language tags, including user defined
extensions for private interchange. This document replaces RFC 3066
(which replaced RFC 1766).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Language Tag . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Language Subtag Sources and Interpretation . . . . . . . . . 5
2.2.1 Pre-Existing RFC3066 Registrations . . . . . . . . . . . . . 11
2.2.2 Possibilities for Registration . . . . . . . . . . . . . . . 12
2.2.3 Classes of Conformance . . . . . . . . . . . . . . . . . . . 13
2.3 Choice of Language Tag . . . . . . . . . . . . . . . . . . . 14
2.4 Meaning of the Language Tag . . . . . . . . . . . . . . . . 15
2.4.1 Language Range . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.2 Matching Language Tags . . . . . . . . . . . . . . . . . . . 17
2.4.3 Canonicalization of Language Tags . . . . . . . . . . . . . 18
2.5 Considerations for Private Use Subtags . . . . . . . . . . . 19
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . 20
3.1 Stability of IANA Registry Entries . . . . . . . . . . . . . 20
3.2 Format of the IANA Language Subtag Registry . . . . . . . . 22
3.3 Registration Procedure for Subtags . . . . . . . . . . . . . 24
3.4 Extensions and Extensions Namespace . . . . . . . . . . . . 27
4. Security Considerations . . . . . . . . . . . . . . . . . . 29
5. Character Set Considerations . . . . . . . . . . . . . . . . 30
6. Changes from RFC3066 . . . . . . . . . . . . . . . . . . . . 31
References . . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 35
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36
B. Examples of Language Tags (Informative) . . . . . . . . . . 37
C. Conversion of the RFC 3066 Language Tag Registry . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . 41
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1. Introduction
Human beings on our planet have, past and present, used a number of
languages. There are many reasons why one would want to identify the
language used when presenting or requesting information.
Information about a user's language preferences commonly needs to be
identified so that appropriate processing can be applied. For
example, the user's language preferences in a brower can be used to
select web pages appropriately. A choice of language preference can
also be used to select among tools (such as dictionaries) to assist
in the processing or understanding of content in different langauges.
In addition, knowledge about the particular language used by some
piece of information content may be useful or even required by some
types of information processing; for example spell-checking,
computer-synthesized speech, Braille transcription, or high-quality
print renderings.
One means of indicating the language used is by labeling the
information content with a language identifier. These identifiers can
also be used to specify user preferences when selecting information
content, or for labeling additional attributes of content and
associated resources.
These identifiers can also be used to indicate additional attributes
of content that are closely related to the language. In particular,
it is often necessary to indicate specific information about the
dialect, writing system, or orthography used in a document or
resource, as these attributes may be important for the user to obtain
information in a form that they can understand, or important in
selecting appropriate processing resources for the given content.
This document specifies an identifier mechanism, a registration
function for values to be used with that identifier mechanism, and a
construct for matching against those values. It also defines a
mechanism for private use extension and how private use, registered
values, and matching interact.
This document replaces RFC 3066, which replaced RFC 1766. For a list
of changes in this document, see: Section 6.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119] [10].
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2. The Language Tag
2.1 Syntax
The language tag is composed of one or more parts: A primary language
subtag and a (possibly empty) series of subsequent subtags. Subtags
are distinguished by their length, position in the subtag sequence,
and content, so that each type of subtag can be recognized solely by
these features. This makes it possible to construct a parser that can
extract and assign some semantic information to the subtags, even if
specific subtag values are not recognized. Thus a parser need not
have an up-to-date copy of the registered subtag values to perform
most searching and matching operations.
The syntax of this tag in ABNF [RFC 2234] [11] is:
= lang *("-" extlang) ["-" script] ["-" region] *("-" variant) *("-" extension) ["-" privateuse]
/ privateuse ; private-use tag
/ grandfathered ; grandfathered registrations
lang = 2*3ALPHA ; shortest ISO 639 code
/ registered-lang
extlang = 3ALPHA ; reserved for future use
script = 4ALPHA ; ISO 15924 code
region = 2ALPHA ; ISO 3166 code
/ 3DIGIT ; UN country number
variant = 5*15alphanum ; registered or private use variants
extension = singleton 1*("-" (2*15alphanum)) ; extension subtag(s)
privateuse = "x" 1*("-" (1*15alphanum)) ; private use subtag(s)
singleton = 1ALPHA ; single letters (except x, which has special meaning)
registered-lang = 4*15ALPHA ; registered language subtag
grandfathered = ALPHA *(alphanum / "-") ; grandfathered registration
alphanum = (ALPHA / DIGIT) ; letters and numbers
Figure 1: Language Tag ABNF
The character "-" is HYPHEN-MINUS (ABNF: %x2D). Whitespace in the
ABNF should be disregarded. For examples of language tags, see
Appendix B. Note that although [RFC 2234] [11] refers to octets, the
language tags described in this document are US-ASCII character
sequences and may be used in documents (such as XML files) that might
use an alternate encodings (such as Unicode UTF-16LE, for example).
The tags and their subtags, including private-use and extensions, are
to be treated as case insensitive: there exist conventions for the
capitalization of some of them, but these should not be taken to
carry meaning. For instance, [ISO 3166] [4] recommends that country
codes be capitalized (MN Mongolia), while [ISO 639] [3] recommends
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that language codes be written in lower case (mn Mongolian). In the
language tags defined by this document, however, the tag 'mn-MN' is
not distinct from 'MN-mn' or 'mN-Mn' (or any other combination) and
each of these variations conveys the same meaning: Mongolian for
Mongolia.
For informative examples of language tags, see Appendix B at the end
of this document.
2.2 Language Subtag Sources and Interpretation
The namespace of language tags and their subtags is administered by
the Internet Assigned Numbers Authority (IANA) [15] according to the
rules in Section 3 of this document.
Terminology in this section:
o Tag or tags refers to a complete language tag, such as
'fr-Latn-CA'
o Subtag refers to a specific section of a tag, separated by hyphen,
such as the subtag 'Latn' in 'fr-Latn-CA'
o Code or codes refers to tags defined in external standards (and
which are used as subtags in this document). For example, 'Latn'
is an ISO 15924 [2] script code (which can be used as a script
subtag in a language tag)
The definitions in this section apply to the various subtags within
the language tags defined by this document, excepting those
"grandfathered" tags defined in Section 2.2.1.
Note that registered subtags can only appear in specific positions in
a tag. Specifically, they can only occur as primary language subtags
or as variant subtags. In addition, sequences of private-use and
extension subtags MUST only occur at the end of the sequence of
subtags and MUST NOT be interspersed with subtags defined elsewhere
in this document.
Each subtag type has unique length and content restrictions that make
identification of the subtag's type possible, even if the content of
the subtag itself is unrecognized. This allows tags to be parsed and
processed without reference to the latest version of the underlying
standards or the IANA registry and makes the associated exception
handling when parsing tags simpler.
Single letter and digit subtags are reserved for current or future
use. These include the following current uses:
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o The single letter subtag "i" is reserved for grandfathered,
IANA-registered primary language subtags, such as "i-enochian".
o The single letter subtag "x" is reserved to introduce a sequence
of private-use subtags. The interpretation of any private-use
subtags is defined solely by private agreement and is not defined
by the rules in this section or in any standard or registry
defined in this document.
o All other single letter subtags are reserved to introduce
standardized extension subtag sequences as described in Section
3.4.
The primary subtag is the first subtag in a language tag and cannot
be empty. Except as noted, the primary subtag is the "language"
subtag. The following rules apply to the assignment and
interpretation of the primary subtag:
o All 2-character subtags in the IANA registry were defined
according to the assignments found in the standard ISO 639, "Code
for the representation of names of languages" [ISO639-1] [3], or
in assignments subsequently made by the ISO 639 Part 1 maintenance
agency or governing standardization bodies.
o All 3-character subtags in the IANA registry were defined
according to the assignments found in ISO 639 Part 2, "Codes for
the representation of names of languages -- Part 2: Alpha-3 code
[ISO 639-2] [1]", or assignments subsequently made by the ISO 639
Part 2 maintenance agency or governing standardization bodies.
o The subtags in the range 'qaa' through 'qtz' are reserved for
private use in language tags. These subtags correspond to codes
reserved by ISO639-2 for private use. These codes SHOULD be used
for non-registered primary-language subtags (instead of using
private-use subtags following "x-"). For example, the tag 'qaa' is
preferred to 'x-someLanguage'. Please refer to Section 2.5 for
more information on private use subtags.
o IANA-registered primary language subtags of 4 to 15 characters in
length MAY also be used to form the primary language subtag. At
the time this document was created, there were no examples of this
kind of subtag and future registrations of this type will be
discouraged: primary languages are STRONGLY RECOMMENDED for
registration with ISO 639 and subtags rejected by ISO 639 will be
closely scrutinized before they are registered with IANA.
o The single character subtag "x" as the primary subtag indicates
that the whole language tag consists of private-use subtags.
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o Other values MUST NOT be assigned to the primary subtag except by
revision or update of this document.
Note: For languages that have both an ISO 639-1 2-character code and
an ISO 639-2 3-character code, only the ISO 639-1 2-character code is
defined.
Note: For languages that have no ISO 639-1 2-character code and for
which the ISO 639-2/T (Terminology) code and the ISO 639-2/B
(Bibliographic) codes differ, only the Terminology code is defined.
At present all languages that have both kinds of 3-character code
also are assigned a 2-character code and hopefully future assignments
of this nature will not arise.
Note: In order to avoid versioning difficulties in applications such
as those experienced in RFC 1766 [8], the ISO 639 Registration
Authority Joint Advisory Committee (RA-JAC) has agreed on the
following policy statement:
"After the publication of ISO/DIS 639-1 as an International Standard,
no new 2-letter code shall be added to ISO 639-1 unless a 3-letter
code is also added at the same time to ISO 639-2. In addition, no
language with a 3-letter code available at the time of publication of
ISO 639-1 which at that time had no 2-letter code shall be
subsequently given a 2-letter code."
This will ensure that, for example, a user who implements "haw"
(Hawaiian), which currently has no 2-character code, will not find
his or her data invalidated by eventual addition of a 2-character
code for that language."
Previously, in RFC 3066 [16], the IANA registry contained whole tag
registrations such as 'cel-gaulish', whereas this document refers to
the registration of subtags, such as 'gaulish'.
One of the grandfathered IANA registrations is "i-enochian". The
subtag "enochian" could be registered as a primary language subtag
(assuming that ISO 639 does not register this language first), making
tags such as "enochian-AQ" and "enochian-Latn" valid.
The following rules apply to the extended language subtags:
o Three letter subtags immediately following the primary subtag are
reserved for future standardization, anticipating work that is
currently under way on ISO 639.
o Extended language subtags MUST follow the primary subtag and
precede any other subtags.
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o There MAY be any additional number of extended language subtags.
o Standardization of the extended language subtags for specific uses
will be by revision or update of this document. Registration of
extended language subtags and non-standard use MUST NOT be
permitted.
Example: In a future revision or update of this document, the tag
'zh-min-nan' (registered under RFC 3066) might become a valid
non-grandfathered tag in which the subtags 'min' and 'nan' might
represent the subdialect 'nan' of the Chinese dialect 'min'.
The following rules apply to the script subtags:
o All 4-character subtags were defined according to ISO 15924
[2]--"Codes for the representation of the names of scripts":
alpha-4 script codes, or subsequently assigned by the ISO 15924
maintenance agency or governing standardization bodies, denoting
the script or writing system used in conjunction with this
language.
o Script subtags MUST immediately follow the primary language subtag
and all extended language subtags and MUST occur before any other
type of subtag described below.
o The subtags Qaaa-Qabx are reserved for private use in language
tags. These subtags correspond to codes reserved by ISO 15924 for
private use. These codes should be used for non-registered script
values. Please refer to Section 2.5 for more information on
private-use subtags.
o Script subtags cannot be registered using the process in Section
3.3 of this document. Variant subtags may be considered for
registration for that purpose.
Example: 'de-Latn' represents German written using the Latin script.
The following rules apply to the region subtags:
o All 2-character subtags following the primary subtag were defined
in the IANA registry according to the assignments found in ISO
3166 [4]--"Codes for the representation of names of countries and
their subdivisions - Part 1: Country codes"--alpha-2 country codes
or assignments subsequently made by the ISO 3166 maintenance
agency or governing standardization bodies.
o All 3-character codes consisting of digit (numeric) characters
were defined in the IANA registry according to the assignments
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found in UN Standard Country or Area Codes for Statistical Use
[5] or assignments made thereto by the governing standards body.
o The region subtag defines language variations used in a specific
region, geographic, or political area. Region subtags MUST follow
any language, extended language, or script subtags and MUST
precede all other subtags.
o There may be at most one region subtag in a language tag.
o Generally the ISO 3166 code is used to form the subtag except for
countries with ambiguous ISO 3166 alpha-2 codes. Please refer to
Section 2.3 for information on the reasons why the UN M49 code may
be canonical for a specific country or region.
o UN numeric codes assigned to 'macro-geographical (continental)' or
sub-regions not associated with an assigned ISO 3166 alpha-2 code
are defined in the IANA registry and are valid for use in language
tags.
o UN numeric codes for 'economic groupings' or 'other groupings' are
not defined in the IANA registry and MUST NOT be used to form
language tags.
o The alphanumeric codes in Appendix X of the UN document are also
undefined and MUST NOT be used. (At the time this document was
created these values match the ISO 3166 alpha-2 codes.)
o The subtags AA, QM-QZ, XA-XZ and ZZ are reserved for private use
in language tags. These subtags correspond to codes reserved by
ISO 3166 for private use. These codes SHOULD be used for private
use region subtags (instead of using a private-use subtag
sequence). For example, the tag 'fr-QM' would be preferred to
'fr-x-someRegion'. Please refer to Section 2.5 for more
information on private use codes.
'de-Latn-CH' represents German written using Latin script for
Switzerland.
'sr-Latn-891' represents Serbian written using Latin script for
Serbia and Montenegro (this country's ISO 3166 alpha2 code 'CS' was
formerly assigned to Czechoslovakia).
'es-419' represents Spanish as spoken in the UN-defined 'Latin
America and Caribbean' region.
The following rules apply to the variant subtags:
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o Variant subtags in the IANA registry are associated with any
external standard. All variant subtags are defined by the
registration process defined in Section 3.3.
o Variant subtags MUST follow all of the other defined subtags, but
precede any extension or private-use subtag sequences.
o Alphanumeric subtags of 5 to 15 characters MAY be registered with
IANA, according to the rules in Section 3.3 of this document.
Previously, in RFC 3066, the IANA registry contained whole tag
registrations such as 'en-boont', whereas this document refers to the
registration of subtags such as 'boont'.
The following rules apply to extensions:
o Extension subtags are separated from the other subtags defined in
this document by a single-letter subtag ("singleton"). The
singleton MUST be one allocated to a registration authority via
the mechanism described in Section 3.4 and cannot be the letter
'x', which is reserved for private-use subtag sequences.
o Note: Private-use subtag sequences starting with the singleton
subtag "x-" are described below.
o An extension MUST follow at least a primary language subtag. That
is, a language tag cannot begin with an extension. Extensions
extend language tags, they do not override or replace them. For
example, the tag 'a-myExtension' is invalid.
o Each singleton subtag MUST appear at most one time in each tag
(other than as a private-use subtag). That is, singleton subtags
MUST NOT be repeated. For example, the tag "en-a-bbb-a-ccc" is
invalid because the subtag "-a" appears twice.
o Extension subtags MUST meet all of the requirements for the
content and format of subtags defined in this document.
o Extension subtags MUST meet whatever requirements are set by the
document that defines their singleton prefix and whatever
requirements are provided by the maintaining authority.
o Each extension subtag MUST be from two to fifteen characters long
and consist solely of letters or digits, with each subtag
separated by a single "-".
o Each singleton MUST be followed by at least one extension subtag.
For example, the tag "tlh-a-b-foo" is invalid because the first
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singleton "a" is followed immediately by another singleton "b".
o Extension subtags MUST follow all language, extended language,
script, region and variant subtags in a tag. (Note: another way of
saying this is that all subtags following the singleton and before
another singleton are part of the extension. Thus in the tag
"fr-a-Latn", the subtag 'Latn' does not represent the ISO 15924
script code for Latin script.)
o In the event that more than one extension appears in a single tag,
the tag SHOULD be canonicalized as described in Section 2.4.3.
o When comparing or matching language tags, extensions MAY be
ignored.
For example, if the prefix "-r" and the shown subtags were defined,
then the following tag would be a valid example:
"en-Latn-GB-boont-r-anExtension-another-x-privatetag"
The following rules apply to private-use subtags:
o Private-use subtags are separated from the other subtags defined
in this document by the reserved single-character subtag "x".
o Private-use subtags MUST follow all language, extended language,
script, region, variant, and extension subtags in the tag. Another
way of saying this is that all subtags following the singleton 'x'
MUST be considered private use. Example: The subtag 'US' in the
tag 'en-x-US' is a private use subtag.
o Unlike Extensions, a tag MAY consist entirely of private-use
subtags.
o No source is defined for private use subtags. Use or
standardization of the private use subtags is by private agreement
and SHOULD NOT be considered part of this document.
For example: Users who wished to utilize SIL Ethonologue for
identification might agree to exchange tags such as
'az-Arab-x-AZE-derbend'. This example contains two private-use
subtags. The first is "AZE" and the second is "derbend".
2.2.1 Pre-Existing RFC3066 Registrations
Existing IANA-registered language tags from RFC 1766 and/or RFC 3066
that are not defined by additions to this document maintain their
validity. IANA will maintain these tags in the registry under the
"grandfathered" type. For more information see Appendix C.
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2.2.2 Possibilities for Registration
Possibilities for registration of subtags include:
o Primary language subtags for languages not listed in ISO 639 that
are not variants of any listed or registered language, can be
registered. At the time this document was created there were no
RFC 3066 examples of this form of subtag. Before attempting to
register a language subtag, there should be a good faith attempt
to register the language with ISO 639. No language subtags will be
registered for codes that exist in ISO 639-1 or ISO 639-2, which
are under consideration by the ISO 639 maintenance or registration
authorities, or which have never been attempted for registration
with those authorities. If ISO 639 has previously rejected a
language for registration, it is reasonable to assume that there
MUST be additional very compelling evidence of need before it will
be registered in the IANA registry (to the extent that it is very
unlikely that any subtags will be registered of this type).
o Dialect or other divisions or variations within a language, its
orthography, writing system, regional variation, or historical
usage may be registered as variant subtags. For example, the
"scouse" subtag (the Scouse dialect of English), was converted
from RFC 3066.
This document leaves the decision on what subtags are appropriate or
not to the registration process described in Section 3.3.
ISO 639 defines a maintenance agency for additions to and changes in
the list of languages in ISO 639. This agency is:
International Information Centre for Terminology (Infoterm)
Aichholzgasse 6/12, AT-1120
Wien, Austria
Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72
ISO 639-2 defines a maintenance agency for additions to and changes
in the list of languages in ISO 639-2. This agency is:
Library of Congress
Network Development and MARC Standards Office
Washington, D.C. 20540 USA
Phone: +1 202 707 6237 Fax: +1 202 707 0115
URL: http://www.loc.gov/standards/iso639
The maintenance agency for ISO 3166 (country codes) is:
ISO 3166 Maintenance Agency
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c/o International Organization for Standardization
Case postale 56
CH-1211 Geneva 20 Switzerland
Phone: +41 22 749 72 33 Fax: +41 22 749 73 49
URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html
The registration authority for ISO 15924 (script codes) is:
Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
URL: http://www.unicode.org/iso15924
The Statistics Division of the United Nations Secretariat maintains
the Standard Country or Area Codes for Statistical Use and can be
reached at:
Statistical Services Branch
Statistics Division
United Nations, Room DC2-1620
New York, NY 10017, USA
Fax: +1-212-963-0623
E-mail: statistics@un.org
URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm
2.2.3 Classes of Conformance
Implementations may wish to express their level of conformance with
the rules and practices described in this document. There are
generally two classes of conforming implementations: "well-formed"
processors and "validating" processors. Claims of conformance SHOULD
explicitly reference one of these definitions.
An implementation that claims to check for well-formed language tags
MUST:
o Check that the tag and all of its subtags, including extension and
private-use subtags, conform to the ABNF or that the tag is on the
list of grandfathered tags.
o Check that singleton subtags that identify extensions do not
repeat. For example, the tag 'en-a-xx-b-yy-a-zz' is not
well-formed.
Well-formed processors are strongly encouraged to implement the
default fallback mechanism in Section 2.4.2 and the associated
canonicalization rules contained in Section 2.4.3.
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An implementation that claims to be validating MUST:
o Check that the tag is well-formed.
o Specify the particular registry date for which the implementation
performs validation of subtags.
o Check that either the tag is a grandfathered tag, or that all
language, script, region, and variant subtags consist of valid
codes for use in language tags according to the IANA registry as
of the particular date specified by the implementation.
o Specify which, if any, extension RFCs as defined in Section 3.4
are supported, including version, revision, and date.
o For any such extensions supported, check that all subtags used in
that extension are valid.
o If the processor generates tags, it MUST do so in canonical form,
including any supported extensions, as defined in Section 2.4.3.
2.3 Choice of Language Tag
One may occasionally be faced with several possible tags for the same
body of text.
Interoperability is best served when all users use the same language
tag in order to represent the same language. If an application has
requirements that make the rules here inapplicable, then that
application risks damaging interoperability. Users of this document
are strongly discouraged against defining their own rules for
language tag choice and matching.
Standards, protocols and applications that reference this document
normatively but apply different rules to the ones given in this
section MUST specify how the procedure varies from the one given
here.
1. Use as precise a tag as possible, but no more specific than is
justified. For example, 'de' might suffice for tagging an email
written in German, while 'de-CH-1996' is probably unnecessarily
precise for such a task.
2. Avoid using subtags that add no distinguishing information about
the content. For example, the script subtag in 'en-Latn-US' is
generally unnecessary, since nearly all English texts are written
in the Latin script.
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3. Use the canonical subtag from the IANA registry in preference to
any of its aliases. For example, you SHOULD use 'he' for Hebrew
in preference to 'iw'.
4. You SHOULD NOT use the UND (Undetermined) code unless the
protocol in use forces you to give a value for the language tag,
even if the language is unknown. Omitting the tag is preferred.
5. You SHOULD NOT use the MUL (Multiple) tag if the protocol allows
you to use multiple languages, as is the case for the
Content-Language header in HTTP.
To ensure consistent backwards compatibility, this document contains
several provisions to account for potential instability in the
standards used to define the subtags that make up langauge tags.
These provisions mean that no language tag created under the rules in
this document will become obsolete. In addition, tags that are in
canonical form will always be in canonical form.
2.4 Meaning of the Language Tag
The language tag always defines a language as spoken (or written,
signed or otherwise signaled) by human beings for communication of
information to other human beings. Computer languages such as
programming languages are explicitly excluded.
If a language tag B contains language tag A as a prefix, then B is
typically "narrower" or "more specific" than A. For example,
'zh-Hant-TW' is more specific than 'zh-Hant'.
This relationship is not guaranteed in all cases: specifically,
languages that begin with the same sequence of subtags are NOT
guaranteed to be mutually intelligible, although they may be. For
example, the tag 'az' shares a prefix with both 'az-Latn'
(Azerbaijani written using the Latin script) and 'az-Cyrl'
(Azerbaijani written using the Cyrillic script). A person fluent in
one script may not be able to read the other, even though the text
might be identical. Content tagged as 'az' most probably is written
in just one script and thus might not be intelligible to a reader
familiar with the other script.
The relationship between the tag and the information it relates to is
defined by the standard describing the context in which it appears.
Accordingly, this section can only give possible examples of its
usage.
o For a single information object, the associated language tags
might be interpreted as the set of languages that is required for
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a complete comprehension of the complete object. Example: Plain
text documents.
o For an aggregation of information objects, the associated language
tags could be taken as the set of languages used inside components
of that aggregation. Examples: Document stores and libraries.
o For information objects whose purpose is to provide alternatives,
the associated language tags could be regarded as a hint that the
content is provided in several languages, and that one has to
inspect each of the alternatives in order to find its language or
languages. In this case, the presence of multiple tags might not
mean that one needs to be multi-lingual to get complete
understanding of the document. Example: MIME multipart/
alternative.
o In markup languages, such as HTML and XML, language information
can be added to each part of the document identified by the markup
structure (including the whole document itself). For example, one
could write C'est la vie. inside a
Norwegian document; the Norwegian-speaking user could then access
a French-Norwegian dictionary to find out what the marked section
meant. If the user were listening to that document through a
speech synthesis interface, this formation could be used to signal
the synthesizer to appropriately apply French text-to-speech
pronunciation rules to that span of text, instead of misapplying
the Norwegian rules.
2.4.1 Language Range
A Language Range is a set of languages whose tags all begin with the
same sequence of subtags. A Language Range can be represented by a
'language-range' tag, by using the definition from HTTP/1.1 [14] :
language-range = language-tag / "*"
That is, a language-range has the same syntax as a language-tag or is
the single character "*". This definition of language-range
implicitly assumes that there is a semantic relationship between tags
that share the same subtag prefixes.
A language-range matches a language-tag if it exactly equals the tag,
or if it exactly equals a prefix of the tag such that the first
character following the prefix is "-". (That is, the language-range
'en-de' matches the language tag 'en-DE-boont', but not the language
tag 'en-Deva'.)
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The special range "*" matches any tag. A protocol which uses language
ranges may specify additional rules about the semantics of "*"; for
instance, HTTP/1.1 specifies that the range "*" matches only
languages not matched by any other range within an "Accept-Language:"
header.
As noted above, not all languages or content denoted by a specific
language-range may be mutually intelligible and this use of a prefix
matching rule does not imply that language tags are assigned to
languages in such a way that it is always true that if a user
understands a language with a certain tag, then this user will also
understand all languages with tags for which this tag is a prefix.
The prefix rule simply allows the use of prefix tags if this is the
case.
2.4.2 Matching Language Tags
Implementations that are searching for content or otherwise matching
language tags to a language-range [Section 2.4.1] may choose to
assume that there is a semantic relationship between two tags that
share common prefixes. This is called 'language tag fallback'. The
most common implementations follow this pattern:
1. When searching for content using language tag fallback, the
language tag is progressively truncated from the end until a
match is located. For example, starting with the tag
'en-US-boont', searchs or matches would first be performed with
the whole tag, then with 'en-US', and finally with 'en'. This
allows some flexibility in finding content in accordance with
Rules 1 and 2 in Section 2.3; allows better maintenance; and
usually provides better results when data is not available at a
specific level of tag granularity or is sparsely populated (than
if the default language for the system or content were used). Any
implementation that uses this technique should ensure that
appropriate data is available on each level.
Tag to match: en-US-boont
1. en-US-boont
2. en-US
3. en
Figure 2: Default Fallback Pattern Example
2. Private-use and Extension subtags are orthogonal to language tag
fallback. By default, implementations SHOULD ignore both
private-use and extension subtags and follow the default fallback
pattern (above). Thus a request to match the tag
"en-US-boont-x-traditional" would produce exactly the same
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information content as the example above.
3. Implementations that choose to interpret one or more private-use
or extension subtags can choose a different fallback pattern or
use the private-use or extension subtags to interpret content in
a different fashion.
4. Implementations that choose not to interpret one or more
private-use or extension subtags SHOULD NOT remove or modify
these extensions in content that they are processing.
5. Any language tag processor MAY match language tags using simple
string comparisons and the default fallback pattern and SHOULD
use this pattern for unrecognized extension subtag sequences that
are processed for matching. When performing canonicalization of
language tags for the purpose of matching, implementations MUST
NOT reorder the subtags within an extension or private-use subtag
sequence.
6. Extension and private-use subtags MAY be ignored when matching or
comparing language tags to a language-range (such as when
performing language negotiation or selecting content).
7. Some applications of language tags may want or need to consider
extensions and private-use subtags when matching tags. If
extensions and private-use subtags are included in a matching
process that utilizes the default fallback mechanism, then the
implementation MUST canonicalize the language tags and/or ranges
before performing the matching. Note that implementations that
claim to be "well-formed" processors as defined in Section 2.2.3
generally fall into this category.
2.4.3 Canonicalization of Language Tags
Since a particular language tag or language-range may be processed
many times, language tags SHOULD always be created or generated in a
canonical form suitable for matching using the default fallback
mechanism.
A language tag is in canonical form when:
1. The tag is well-formed according the rules in Section 2.1 and
Section 2.2.
2. None of the subtags in the language tag has a canonical mapping
in the IANA registry.
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3. If more than one extension subtag sequence exists, the extension
sequences are ordered into case-insensitive ASCII order by
singleton subtag.
For example, the language tag "en-A-aaa-B-ccc-bbb-x-xyz" is in
canonical form, while "en-B-ccc-bbb-A-aaa-X-xyz" is well-formed but
not in canonical form.
Note: Canonicalization of language tags does not imply anything about
the use of upper or lowercase letter in subtags as described in
Section 2.1. All comparisons MUST be performed in a case-insensitive
manner.
An extension MUST define any relationships that may exist between the
various subtags in the extension and thus MAY define an alternate
canonicalization scheme for the extension's subtags. Extensions MAY
define how the order of the extension's subtags are interpreted. For
example, an extension could define that its subtags are in canonical
order when the subtags are placed into ASCII order: that is,
"en-a-aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension
might define that the order of the subtags influences their semantic
meaning (so that 'en-b-ccc-bbb-aaa' has a different value than
'en-b-aaa-bbb-ccc').
2.5 Considerations for Private Use Subtags
Private-use codes and subtags require private agreement between the
parties that intend to use or exhange language tags that use them and
great caution should be used in employing them in content or
protocols intended for general use. Private-use subtags are simply
useless for information exchange without prior arrangement.
The value and semantic meaning of private-use tags and of the
subtags used within such a language tag are not defined by this
document.
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3. IANA Considerations
This section deals with the processes and requirements necessary to
maintain the registry of subtags and extensions for use in language
tags as defined by this document and in accordance with the
requirements of RFC 2434 [13].
The language subtag registry will be maintained so that, except for
extension subtags, it is possible to validate all of the subtags that
appear in a language tag under the provisions of this document or its
revisions or sucessors. In addition, the meaning of the various
subtags will be unambiguous and stable over time. (The meaning of
private-use subtags, of course, is not defined by the IANA registry.)
The previous registry under RFC 3066 contained only a few registered
tags. The new registry, under this document, contains a comprehensive
list of all of the subtags valid in language tags. This allows
implementers a straightfoward and reliable way to validate language
tags.
The impact on the IANA maintainers of the registry will be a small
increase in the frequency of new entries after the initial conversion
of the registry as described in Appendix C. The initial set of
records will be created by the process described in Appendix C and
should represent no impact on IANA.
3.1 Stability of IANA Registry Entries
The stability of the registry and the subtags it defines is critical
to the long term stability of language tags. Assignments to the IANA
Language Subtag Registry MUST follow the following stability rules.
(These rules specifically deal with potential instability in ISO 639,
ISO 15924, and ISO 3166 due to withdrawl or deprecation of existing
codes and their subsequent reassigment, as well as the interaction
between registrations and these standards):
o Once assigned in the IANA registry, no part of a subtag's
definition (except for the "notes" field and additions to the
"recommended prefix" field) may be changed. This means that ISO
639, ISO 15924, and ISO 3166 codes that are withdrawn by the
respective maintenance or registration authority remain valid in
language tags. It also means that subtags cannot be assigned a
canonical equivalent or alias, except when they are created. This
means that canonical language tags are stable: they will never
become non-canonical as a result of future registrations or
changes in the registry.
o If ISO 639, ISO 15924, or ISO 3166 assign a new code (not in the
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IANA language subtag registry) a meaning equivalent to that of a
code already defined in the IANA registry for that type, then the
corresponding new subtag MUST have a canonical alias of the
existing subtag.
1. If ISO 3166 were to assign the code 'QX' to represent the
value "Isle of Man" (represented in the IANA registry by the
UN M49 code '833'), '833' remains the canonical subtag and
'QX' would be assigned '833' as an alias. This prevents tags
that are in canonical form from becoming non-canonical.
2. If the tag 'enochian' were registered as a primary language
subtag and ISO 639 subsequently assigned an alpha-3 code to
the same language, the new ISO 639 code would be entered into
the IANA registry with a canonical mapping to 'enochian'. The
new ISO code can be used, but it is not canonical.
o Stability provisions apply to grandfathered tags with this
exception: should all of the subtags in a grandfathered tag become
valid subtags in the IANA registry, then the grandfathered tag
MUST be deprecated. Note that this will not affect language tags
that match the grandfathered tag, since these tags will match
valid subtag sequences. For example, if the subtags 'min' and
'nan' in the language tag 'zh-min-nan' be registered as extended
language subtags, then the grandfathered tag 'zh-min-nan' would be
deprecated (but existing content or implementations that use
'zh-min-nan' would remain valid.
o If ISO 639, ISO 15924, or ISO 3166 reassign a code that is in the
IANA registry under the same category (which generally means that
it was previously withdrawn by the maintenance or registration
authority), then the new subtag MUST NOT be registered and an
alternative subtag MUST be created according to the following
rules:
1. In the event that either ISO 639 or ISO 15924 assigns a new
meaning to an existing code, the Language Subtag Reviewer, as
described in Section 3.3, shall prepare a proposal for
entering in the IANA registry as soon as practical a
registered language or variant subtag as an alternate value
for the new code. The form of the registered language subtag
or variant subtag will be at the discretion of the language
subtag reviewer and must conform to other restrictions on
language or variant subtags in this document.
2. In the event ISO 3166 assigns a new meaning to an existing
code, then the language subtag reviewer, as described in
Section 3.3, shall prepare a proposal for entering the
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appropriate numeric UN country code as an entry in the IANA
registry. If there is not an available UN numeric code with
the proper meaning, then the language subtag reviewer SHALL
petition the UN to create one. If there is not a timely
response from the UN, then a registered variant code SHALL be
registered, as in #1 above.
3. The normal registration process described in Section 3.3 of
this document applies to the review and registration of the
registered subtags described above. Note that these subtags
should never be used in combination with the subtag type for
which they are an alternate. For example, a "script" variant
subtag should not be used with a script subtag.
3.2 Format of the IANA Language Subtag Registry
The IANA Language Subtag Registry will consist of a text file that is
machine readable in the format described in this section, plus copies
of the registration forms approved by the Language Subtag Reviewer in
accordance with the process described in Section 3.3. With the
exception of the registration forms for grandfathered tags, no
registration records will be maintained for the initial set of
subtags.
Each record in the subtag registry will consist of a series of fields
separated by semi-colons and terminated by a newline. Text appearing
after a "#" symbol contains comments. Whitespace surrounding fields
in the file is ignored. Lists inside a field are comma separated.
The fields in each record, in order, are:
type; subtag; description; date; canonical_value; recommended_prefix
# comments
o Semicolons delimit the fields.
o Empty fields (and their semicolons) at the end of the record may
be omitted.
o Leading or trailing whitespace in each field is not part of the
content.
o When the type is "grandfathered", then the subtag field is
actually a whole tag.
o The recommended_prefix is empty, except where the type is
"variant"
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o Notes are always presented as comments at the end, after a hash
mark.
# language codes: ISO 639 and registered codes
language; aa; Afar; 2004-06-28; ;
language; he; hebrew; 2004-06-28; ;
language; iw; hebrew; 2004-06-28; he ; #note mapping
language; seuss; Hypothetical Language; 2005-04-01 ; ;# registered language
# script codes: ISO 15924
script; Arab; Arabic; 2004-06-28; ;
script; Armn; Armenian; 2004-06-28; ;
# region codes: ISO 3166 and UN codes
region; AF; Afghanistan; 2004-06-28; ;
region; CS; Czechoslovakia; 2004-06-28; ;
region; YU; Yugoslavia; 2004-06-28; ;
region; 891; Serbia and Montenegro; 2004-06-28; ;
# registered variants
variant; boont; Boontling; 2004-06-28; ; en #boont variant of English
#grandfathered from RFC 3066
grandfathered; de-CH-1996; German Swiss variant orthography of 1996; 2001-07-17; ;
Figure 3: Example of the Registry Format
The field 'type' MUST consist of one of the following strings:
"language", "extlang", "script", "region", "variant", and
"grandfathered" and denotes the type of subtag (or tag, in the case
of grandfathered).
The field 'subtag' contains the subtag being defined.
The field 'description' contains a description of the subtag
transcribed into ASCII.
The field 'date' contains the date the record was added to the
registry in ISO 8601 format. For example: 2004-06-28 represents June
28, 2004, in the Gregorian calendar.
The field 'canonical value' represents a canonical mapping of this
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record to a subtag record of the same 'type'. Note that this field
MUST NOT be modified: therefore a subtag whose record contains no
canonical mapping when the record is created is a canonical form and
will remain so.
The field 'recommended prefix' is for use with registered variants
and contains a comma separated list of language-ranges considered
most appropriate for use with this subtag. Additional values can be
added to this field for variants only via additional registration.
Other modification of this field (such as removing or changing
values) is not permitted.
Notes and comments may contain additional information about the
subtag, as deemed appropriate for understanding the registry and
implementing language tags using the various subtags. These values
can be changed via the registration process and no guarantee of
stability is provided.
Maintenance of the registry requires that as new codes are assigned
by ISO 639, ISO 15924, and ISO 3166, the Language Subtag Reviewer
will evaluate each assignment, determine whether it conflicts with
existing registry entries, and submit the information to IANA for
inclusion in the registry.
The Language Subtag Reviewer MUST ensure that new subtags meet the
requirements in Section 2.3 or submit an appropriate alternate code
as described in that section. She or he will use the following form
to submit this information:
LANGUAGE SUBTAG REGISTRATION FORM (NEW RECORD)
Record Text:
Type:
Subtag:
Description:
Date:
Canonical Mapping:
Recommended Prefix:
Note:
Figure 4
The field 'record text' contains the exact record that IANA is to
insert into the Language Subtag Registry. The contents of the
remaining fields must exactly match those in this field.
3.3 Registration Procedure for Subtags
The procedure given here MUST be used by anyone who wants to use a
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subtag not given an interpretation in Section 2.2 of this document or
previously registered with IANA.
Only primary language and variant subtags will be considered for
registration. (Subtags required for stability are the only exception
to this. See Section 3.1.)
This procedure MAY also be used to register or alter the information
for the "note" or "recommended prefix" fields in a subtag's record as
described in Figure 3. Changes to all other fields in the IANA
registry is NOT permitted.
If registering a new language subtag, the process starts by filling
out the registration form reproduced below. Note that each response
is not limited in size and should take the room necessary to
adequately describe the registration.
LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester:
2. E-mail address of requester:
3. Subtag to be registered:
4. Type of Registration:
[ ] language
[ ] variant
5. Description of subtag (in English or transcribed into ASCII):
6. Intended meaning of the subtag:
7. Recommended prefix(es) of subtag (for variants):
8. Native name of the language or variation (transcribed into ASCII):
9. Reference to published description of the language (book or article):
10. Any other relevant information:
Figure 5
The subtag registration form MUST be sent to
for a two week review period before it can
be submitted to IANA. (This is an open list. Requests to be added
should be sent to .)
Variant subtags are generally registered for use with a particular
language range (see Section 2.4.2. For example, the subtag 'boont' is
intended for use with language tags that match the language range
'en', since Boontling is a dialect of English. In other words, the
subtag boont is intended for use in tags that start with 'en' and
could include tags such as 'en-Latn-boont' or 'en-US-boont'. This
information MUST be provided in the registration form.
Any registered subtag MAY be incorporated into a variety of language
tags, according to the rules of Section 2.1. This makes validation
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simpler and thus more uniform across implementations, and does not
require new registrations for different intended language ranges.
The intended language ranges for a given registered subtag will be
maintained in the IANA registry as a guide to usage. If it is
necessary to add an additional intended language range to that list
for an existing language tag, that can be done by filing an
additional registration form. In that form, the "Any other relevant
information:" field should indicate that it is the addition of an
additional intended language range.
Requests to add a language range to a subtag that imply a different
semantic meaning will be rejected. For example, if a request were
made to add the language range 'de' to the subtag 'nedis' so that the
tag 'de-nedis' represented some German dialect would be rejected
because it would change the semantic meaning assigned to the subtag.
A separate subtag SHOULD be created for such instances.
When the two week period has passed, the subtag reviewer, who is
appointed by the IESG, either forwards the request to IANA@IANA.ORG,
or rejects it because of significant objections raised on the list or
due to problems with constraints in this document (which should be
explicitly cited). Note that the reviewer can raise objections on the
list if he or she so desires. The important thing is that the
objection must be made publicly.
The applicant is free to modify a rejected application with
additional information and submit it again; this restarts the two
week comment period.
Decisions made by the reviewer may be appealed to the IESG [RFC 2028]
[9] under the same rules as other IETF decisions [RFC 2026] [18]. All
registered forms are available online in the directory http://
www.iana.org/numbers.html under "languages".
Updates of registrations follow the same procedure as registrations.
The subtag reviewer decides whether to allow a new registrant to
update a registration made by someone else; normally objections by
the original registrant would carry extra weight in such a decision.
Registrations are permanent and stable. Once registered, subtags will
not be removed from the registry and will remain the canonical method
of referring to a specific language or variant. This provision does
not apply to grandfatered tags, which may become deprecated due to
registration of subtags.
Note: The purpose of the "published description" is intended as an
aid to people trying to verify whether a language is registered, or
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what language a particular subtag refers to. In most cases, reference
to an authoritative grammar or dictionary of that language will be
useful; in cases where no such work exists, other well known works
describing that language or in that language may be appropriate. The
subtag reviewer decides what constitutes "good enough" reference
material. This requirement is not intended to exclude particular
languages or dialects due to the size of the speaker population or
lack of a standardized orthography. Minority languages will be
considered equally on their own merits.
3.4 Extensions and Extensions Namespace
Extension subtags are those introduced by single-letter subtags other
than 'x-'. They are reserved for the generation of identifiers which
contain a language component, and are compatible with applications
that process language tags according to this specification. For
example, they might be used to define locale identifiers, which are
generally based on language.
The structure and form of extensions are defined by this document so
that implementations can be created that are forward compatible with
applications that may be created using single-letter subtags in the
future. In addition, defining a mechanism for maintaining
single-letter subtags will lend to the stability of this document by
reducing the likely need for future revisions or updates.
IANA will maintain a registry of allocated single-letter subtags.
This registry contain the following information: letter identifier;
name; purpose; RFC defining the subtag namespace and its use; and the
name, URL, and email address of the maintaining authority.
Allocation of a single-letter subtag shall take the form of an RFC
defining the name, purpose, processes, and procedures for maintaining
the subtags. The maintaining or registering authority, including
name, contact email, discussion list email, and URL location of the
registry must be indicated clearly in the RFC. The RFC MUST specify
each of the following:
o The specification MUST reference the specific version or revision
of this document that govern its creation and MUST reference this
section of this document.
o The specification and all subtags defined by the specification
MUST follow the ABNF and other rules for the formation of tags and
subtags as defined in this document. In pariticular it MUST
specify that case is not significant.
o The specification MUST specify a canonical representation and this
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canonical representation SHOULD NOT conflict with any of the
matching or fallback mechanisms defined in this document.
o The specification of valid subtags MUST be available over the
Internet and at no cost.
o The specification MUST be in the public domain or available via a
royalty-free license acceptable to the IETF and specified in the
RFC.
o The specification MUST be versioned and each version of the
specification MUST be numbered, dated, and stable.
o The specification MUST be stable. That is, extension subtags, once
defined by a specificaiton, MUST NOT be retracted or change in
meaning in any substantial way.
o IANA MUST be informed of changes to the contact information and
URL for the specification.
The determination of whether an Internet-Draft meets the above
conditions and the decision to grant or withhold such authority rests
solely with the IESG, and is subject to the normal review and appeals
process associated with the RFC process.
Extension authors are strongly cautioned that many (including most
well-formed) processors will be unaware of any special relationships
or meaning inherent in the order of extension subtags. Extension
authors SHOULD avoid subtag relationships or canonicalization
mechanisms that interfere with the default fallback mechansm. For
example, if the subtag 'aaa' were least significant in the tag
'fr-c-aaa-bbb-ccc'.
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4. Security Considerations
The only security issue that has been raised with language tags since
the publication of RFC 1766, which stated that "Security issues are
believed to be irrelevant to this memo", is a concern with language
ranges used in content negotiation - that they may be used to infer
the nationality of the sender, and thus identify potential targets
for surveillance.
This is a special case of the general problem that anything you send
is visible to the receiving party. It is useful to be aware that such
concerns can exist in some cases.
The evaluation of the exact magnitude of the threat, and any possible
countermeasures, is left to each application protocol.
Although the specification of valid subtags for an extension MUST be
available over the Internet, implementations SHOULD NOT mechanically
depend on it being always accessible, to prevent denial-of-service
attacks.
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5. Character Set Considerations
The syntax in this document requires that language tags use only the
characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most
character sets, so presentation of language tags should not have any
character set issues.
The issue of deciding upon the rendering of characters based on the
language tag is not addressed in this memo; however, if different
spans of text are not marked with font information, it may be useful
to provide the ability to mark spans of text with language. For
example, a rendering engine may use that information in deciding
which font to use in displaying Han-based ideographs when it
encounters mixed Japanese-Chinese text that has no attached font
information.
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6. Changes from RFC3066
The main goals were to maintain backward compatibility (so that all
previous codes would remain valid); reduce the need for large numbers
of registrations; to provide a more formal structure to allow parsing
into subtags even where software does not have the latest
registrations; to provide stability in the face of potential
instability in ISO 639, 3166, and 15924 codes (*demonstrated
instability* in the case of ISO 3166); and to allow for external
extension mechanisms.
o Allows ISO 15924 script code subtags and allows them to be used
generatively.
o Adds the concept of a variant subtag and allows variants to be
used generatively.
o Adds an extension mechanism including both private-use and
standardized extensions.
o Defines the private-use tags in ISO 639, ISO 15924, and ISO 3166
as the mechanism for creating private-use language, script, and
region subtags respectively
o Defines a syntax for private-use variant subtags which can be used
without registration.
o Defines an extended language subtag for use with certain
anticipated features of ISO 639-3.
o Defines a process for handling reuse of values by ISO 639, ISO
15924, and ISO 3166 in the event that they register a previously
used value for a new purpose.
o Changes the IANA language tag registry to a language subtag
registry
o Makes the choice of UN or ISO 3166 codes explicit in Section 2.2
and modified the text of Rule 7a. It also sets a start date for
ambiguity resolution.
o Expands the maximum size of some of the subtags, including the
primary subtag. In RFC 3066 the maximum subtag length was eight
characters long. In this document the maximum length for most
subtags is fifteen characters (and is thirty-one characters for
extensions and private-use subtags).
o Added the concept of well-formed vs. validating processors,
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defining the rules by which an implementation can claim to be one
or the other. This affects applications that perform matching in
particular.
o Provided a complete list of valid subtags in the IANA registry to
allow for robust implementation and ease of maintenance.
Ed Note: The following items are provided for the convenience of
reviewers and will be removed from the final document.
Changes between draft-03 and this version are:
o Modified ABNF to better reflect private_use actual usage.
(M.Davis)
o Added hyphen in phrase "IANA-registered" (P.Constable)
o Modified the text related to ISO 639 private-use tags in language
choice to make it clear that 'qaa' (or similar) is preferred to
'x-someTag'. (P.Constable)
o Modified the section on region subtags to make what is denoted
clearer. This also resulted in some minor editorial wording
changes. (P.Constable)
o In section 2.4, revised so that we always used "associated tags"
instead of the singular "tag". This makes the examples much
clearer. (P.Constable)
o In section 2.4.1, revised so that language-ranges are more clearly
defined and removed the references to "sets", which was rather
confusing. (P.Constable)
o Modified the Section 2.4.3 so that it is clear that
canonicalization must be performed when matching and is
recommended when generating. In addition, the canonicalization
rules were cleaned up so that they are clearer, (P.Constable)
o The term 'obsoleted' was replaced with the term 'superseded' in
the section on processing the RFC 3066 registry. (P.Constable)
o A note was added about casing in the section on canonicalization.
(A.Phillips)
o Added the concept of well-formed vs. validating to section on
choice, defining the rules by which an implementation can claim to
be one or the other. This affects applications that perform
matching in particular. (M.Davis/A.Phillips)
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o Spelled 'superceded' as 'superseded' (J.Cowan)
o Replaced references to 'i-hakka' with 'i-enochian' (D.Ewell)
o Canonicalized RFC and ISO references. (D.Ewell)
o Slightly reworded the reference to 'zh-min-nan' in the extended
language example to make it clear that this is not currently a
valid extended language series of subtags (and how it could become
one). (D.Ewell)
o Changes to force extensions to adhere closely to this document and
to specify a canonicalization mechanism. (M.Davis)
o Changes to the character sets section to make clear that language
tags must always use (subset of) ASCII and to make the example
slightly clearer. (A.Phillips/M.Davis)
o Additions to the requirements for validating processors, making
them validate registrations and canonicalized correctly. (M.Davis)
o Corrected the registration form to remove a lingering reference to
extended language subtags. (A.Phillips)
o Modified the intro to the IANA Considerations section (section 3)
because it now does more than just subtag registration.
(A.Phillips)
o Changed the ABNF to make it consistent with RFC 2234 according to
Harald's information (H.Alvestrand).
o Fixed the definition of validating processors to deal with the
changes in the IANA registry. (A.Phillips and M.Davis)
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References
[1] International Organization for Standardization, "ISO 639-2:1998
- Codes for the representation of names of languages -- Part 2:
Alpha-3 code - edition 1", August 1988.
[2] ISO TC46/WG3 and M. Everson, Ed., "ISO 15924:2003 (E/F) - Codes
for the representation of names of scripts", March 2003.
[3] International Organization for Standardization, "Code for the
representation of names of languages, 1st edition", ISO
Standard 639, 1988.
[4] International Organization for Standardization, "Codes for the
representation of names of countries, 3rd edition", ISO
Standard 3166, August 1988.
[5] Statistical Division, United Nations, "Standard Country or Area
Codes for Statistical Use", UN Standard Country or Area Codes
for Statistical Use, Revision 4 (United Nations publication,
Sales No. 98.XVII.9, June 1999.
[6] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021
and RFC 822", RFC 1327, May 1992.
[7] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing
the Format of Internet Message Bodies", RFC 1521, September
1993.
[8] Alvestrand, H., "Tags for the Identification of Languages", RFC
1766, March 1995.
[9] Hovey, R. and S. Bradner, "The Organizations Involved in the
IETF Standards Process", BCP 11, RFC 2028, October 1996.
[10] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[11] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[12] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[13] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
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1998.
[14] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[15] Carpenter, B., Baker, F. and M. Roberts, "Memorandum of
Understanding Concerning the Technical Work of the Internet
Assigned Numbers Authority", RFC 2860, June 2000.
[16] Alvestrand, H., "Tags for the Identification of Languages", BCP
47, RFC 3066, January 2001.
[17] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003.
[18]
Authors' Addresses
Addison Phillips (editor)
webMethods, Inc.
432 Lakeside Drive
Sunnyvale, CA 94088
US
EMail: aphillips@webmethods.com
Mark Davis
IBM
EMail: mark.davis@us.ibm.com
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Appendix A. Acknowledgements
Any list of contributors is bound to be incomplete; please regard the
following as only a selection from the group of people who have
contributed to make this document what it is today.
The contributors to RFC 3066 and RFC 1766, the precursors of this
document, made enormous contributions directly or indirectly to this
document and are generally responsible for the success of language
tags.
The following people (in alphabetical order) contributed to this
document or to RFCs 1766 and 3066:
Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet,
Nathaniel Borenstein, Eric Brunner, Sean M. Burke, Jeremy Carroll,
John Clews, Jim Conklin, Peter Constable, John Cowan, Mark Crispin,
Dave Crocker, Martin Duerst, Michael Everson, Doug Ewell, Ned Freed,
Tim Goodwin, Dirk-Willem van Gulik, Marion Gunn, Paul Hoffman,
Richard Ishida, Olle Jarnefors, Kent Karlsson, John Klensin, Alain
LaBonte, Eric Mader, Keith Moore, Chris Newman, Masataka Ohta, George
Rhoten, Markus Scherer, Keld Jorn Simonsen, Thierry Sourbier, Otto
Stolz, Tex Texin, Rhys Weatherley, Misha Wolf, Francois Yergeau and
many, many others.
Very special thanks must go to Harald Tveit Alvestrand, who
originated RFCs 1766 and 3066, and without whom this document would
not have been possible. Special thanks must go to Michael Everson,
who has served as language tag reviewer for almost the complete
period since the publication of RFC 1766.
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Appendix B. Examples of Language Tags (Informative)
Simple language code:
de (German)
fr (French)
ja (Japanese)
Language code plus Script code :
zh-Hant (Traditional Chinese)
en-Latn (English written in Latin script)
sr-Cyrl (Serbian written with Cyrillic script)
Language-Script-Region:
zh-Hans-CN (Simplified Chinese for the PRC)
sr-Latn-891 (Serbian, Latin script, Serbia and Montenegro)
Language-Script-Region-Variant:
en-Latn-US-boont (Boontling dialect of English)
Language-Region:
de-DE (German for Germany)
zh-SG (Chinese for Singapore)
cs-CS (Czech for Czechoslovakia)
sr-891 (Serbian for Serbia and Montenegro, UN country code, see 7a
in Section 2.3
Other Mixtures:
zh-CN (Chinese for the PRC)
en-boont (Boontling dialect of English)
private-use mechanism:
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de-CH-x-phonebook
az-Arab-x-AZE-derbend
Extended language subtags (examples ONLY: extended languages must be
defined by revision or update to this document):
zh-min
zh-min-nan-Hant-CN
Private-use tags:
qaa-Qaaa-QM-xsouthern (all private tags)
de-Qaaa (German, with a private script)
de-Latn-QM (German, Latin-script, private region)
de-Qaaa-DE (German, private script, for Germany)
Tags that use extensions (examples ONLY: extensions must be defined
by revision or update to this document or by RFC):
o en-US-u-gregorianCalendar
o zh-CN-x-privateUse
o en-a-anExtension-b-another
Some Invalid Tags:
de-891-DE (two region tags)
a-DE (use of a single character tag in primary position)
zh-xsouthern-DE (private-use variant followed by another tag)
ar-a-aaa-b-bbb-a-ccc (two extensions with same single letter
prefix)
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Appendix C. Conversion of the RFC 3066 Language Tag Registry
Upon publication of this document as a BCP, the existing IANA
language tag registry must be converted into the new subtag registry.
This section defines the process for performing this conversion.
When this document is published, an email request will be sent to the
list ietf-languages@iana.org requesting the conversion of the
registry from the authors of this document. In that request, the
authors of this document will provide a URL whose referred content is
the proposed IANA Language Subtag Registry following conversion.
Tags that are currently deprecated will be maintained as
grandfathered entries. A note should be added indicating that they
are 'deprecated' and the original note indicating why the tag was
deprecated left in place.
Tags that consist entirely of subtags that are valid under this
document and which have the correct form and format for tags defined
by this document are marked as 'superseded' by this document. For
example, zh-Hant is now defined by this document.
Tags that contain subtags which are consistent with registration
under the guidelines in this document will have a new subtag
registration created for each eligible subtag. If all of the subtags
in the original tag are fully defined by the resulting registrations
or by this document, then the original tag is marked as 'superseded'
by this document. For example, en-boont will result in a new subtag
"boont".
Tags that contain one or more subtags that do not match the valid
registration pattern and which are not otherwise defined by this
document are marked as 'grandfathered' by this document.
There will be a reasonable period in which the community may comment
on the proposed list entries, which SHALL be no less than two weeks
in length. At the completion of this period, the Language Subtag
Reviewer will notify IANA@IANA.ORG and the ietf-languages mail lists
that the task is complete and forward the necessary materials to IANA
for publication.
Registrations that are in process under the rules defined in RFC 3066
MAY be completed under the former rules, at the discretion of the
language tag reviewer. Any new registrations submitted after the
request for conversion of the registry MUST be rejected.
All existing RFC 3066 language tag registrations will be maintained
in perpetuity.
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The rules governing the conversion of RFC 1766 and RFC 3066
registered tags are:
o If the formerly registered tag would now be defined by this
document, then the existing tag is marked as superseded by this
document and no subtag will be registered as a result. For
example, 'zh-Hans' is now defined by the addition of ISO 15924
script codes.
o If the registered tag contained one or more subtags that follow
the guidelines for registered language or variant subtags, and all
of the subtags are either now defined by this document or would be
valid to register, then each subtag not already covered by this
document will be registered automatically by IANA without further
review and the existing tag marked as superseded by this document.
For example: the tag 'en-boont' fits the pattern for a registered
variant. The variant subtag "boont" will be registered
automatically and 'en-boont' marked as superseded.
o If the registered tag contains any subtags that are not otherwise
valid for registration according to the rules in this document,
then the tag as a whole is maintained as an exceptional case (that
is, it is "grandfathered"). This includes special cases of Sign
Language tags. For example, the tag 'zh-min-nan' is not covered by
any addition and is grandfathered, as is 'sgn-BE-fr' (Belgian
French Sign Language).
Users of tags that are grandfathered should consider registering
appropriate subtags in the IANA subtag registry (but are not required
to).
Where two subtags have the same meaning, the priority of which to
make canonical SHALL be the following:
o As of March 1995 (the issue date for RFC 1766), if a code exists
in the associated ISO standard and it is not deprecated or
withdrawn as of that date, then it has priority.
o Otherwise, the earlier-registered tag in the associated ISO
standard has priority.
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