Subject: [Ltru] submission: draft-ietf-ltru-4646bis-02

From: Addison Phillips <[email-masked]>
Date: Mon, 18 Dec 2006 16:34:03 -0800

Dear Editors,

Please find attached in text format draft-02 of draft-ietf-ltru-4646bis.

Best Regards,

Addison (for the editors)

-- 
Addison Phillips
Globalization Architect -- Yahoo! Inc.

Internationalization is an architecture.
It is not a feature.

Network Working Group                                   A. Phillips, Ed.
Internet-Draft                                               Yahoo! Inc.
Obsoletes: 4646 (if approved)                              M. Davis, Ed.
Expires: June 21, 2007                                            Google
                                                       December 18, 2006

                     Tags for Identifying Languages
                       draft-ietf-ltru-4646bis-02

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Copyright Notice

   Copyright (C) The Internet Society (2006).

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 the
   creation of user-defined extensions for private interchange.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  The Language Tag . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Language Subtag Sources and Interpretation . . . . . . . .  8
       2.2.1.  Primary Language Subtag  . . . . . . . . . . . . . . .  9
       2.2.2.  Extended Language Subtags  . . . . . . . . . . . . . . 11
       2.2.3.  Script Subtag  . . . . . . . . . . . . . . . . . . . . 12
       2.2.4.  Region Subtag  . . . . . . . . . . . . . . . . . . . . 12
       2.2.5.  Variant Subtags  . . . . . . . . . . . . . . . . . . . 14
       2.2.6.  Extension Subtags  . . . . . . . . . . . . . . . . . . 15
       2.2.7.  Private Use Subtags  . . . . . . . . . . . . . . . . . 17
       2.2.8.  Grandfathered Registrations  . . . . . . . . . . . . . 17
       2.2.9.  Classes of Conformance . . . . . . . . . . . . . . . . 18
   3.  Registry Format and Maintenance  . . . . . . . . . . . . . . . 20
     3.1.  Format of the IANA Language Subtag Registry  . . . . . . . 20
       3.1.1.  File Format  . . . . . . . . . . . . . . . . . . . . . 20
       3.1.2.  Record Definitions . . . . . . . . . . . . . . . . . . 21
       3.1.3.  Subtag and Tag Fields  . . . . . . . . . . . . . . . . 23
       3.1.4.  Description Field  . . . . . . . . . . . . . . . . . . 24
       3.1.5.  Deprecated Field . . . . . . . . . . . . . . . . . . . 25
       3.1.6.  Preferred-Value Field  . . . . . . . . . . . . . . . . 25
       3.1.7.  Prefix Field . . . . . . . . . . . . . . . . . . . . . 26
       3.1.8.  Comments Field . . . . . . . . . . . . . . . . . . . . 26
       3.1.9.  Suppress-Script Field  . . . . . . . . . . . . . . . . 26
     3.2.  Language Subtag Reviewer . . . . . . . . . . . . . . . . . 27
     3.3.  Maintenance of the Registry  . . . . . . . . . . . . . . . 27
     3.4.  Stability of IANA Registry Entries . . . . . . . . . . . . 29
     3.5.  Registration Procedure for Subtags . . . . . . . . . . . . 33
     3.6.  Possibilities for Registration . . . . . . . . . . . . . . 36
     3.7.  Extensions and Extensions Registry . . . . . . . . . . . . 38
     3.8.  Update of the Language Subtag Registry . . . . . . . . . . 41
   4.  Formation and Processing of Language Tags  . . . . . . . . . . 42
     4.1.  Choice of Language Tag . . . . . . . . . . . . . . . . . . 42
     4.2.  Meaning of the Language Tag  . . . . . . . . . . . . . . . 44
     4.3.  Length Considerations  . . . . . . . . . . . . . . . . . . 45
       4.3.1.  Working with Limited Buffer Sizes  . . . . . . . . . . 46
       4.3.2.  Truncation of Language Tags  . . . . . . . . . . . . . 47
     4.4.  Canonicalization of Language Tags  . . . . . . . . . . . . 47
     4.5.  Considerations for Private Use Subtags . . . . . . . . . . 49
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 51
     5.1.  Language Subtag Registry . . . . . . . . . . . . . . . . . 51
     5.2.  Extensions Registry  . . . . . . . . . . . . . . . . . . . 51
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 53
   7.  Character Set Considerations . . . . . . . . . . . . . . . . . 54
   8.  Changes from RFC 4646  . . . . . . . . . . . . . . . . . . . . 55
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 57

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     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 57
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 58
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 60
   Appendix B.  Examples of Language Tags (Informative) . . . . . . . 61
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 64
   Intellectual Property and Copyright Statements . . . . . . . . . . 65

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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.

   A user's language preferences often need to be identified so that
   appropriate processing can be applied.  For example, the user's
   language preferences in a Web browser can be used to select Web pages
   appropriately.  Language preferences can also be used to select among
   tools (such as dictionaries) to assist in the processing or
   understanding of content in different languages.

   In addition, knowledge about the particular language used by some
   piece of information content might be useful or even required by some
   types of 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 an identifier or "tag".  These tags can be
   used to specify user preferences when selecting information content,
   or for labeling additional attributes of content and associated
   resources.

   Tags can also be used to indicate additional language attributes of
   content.  For example, indicating specific information about the
   dialect, writing system, or orthography used in a document or
   resource may enable the user to obtain information in a form that
   they can understand, or it can be important in processing or
   rendering the given content into an appropriate form or style.

   This document specifies a particular identifier mechanism (the
   language tag) and a registration function for values to be used to
   form tags.  It also defines a mechanism for private use values and
   future extension.

   This document replaces [RFC4646], which replaced [RFC3066] and its
   predecessor [RFC1766].  For a list of changes in this document, see
   Section 8.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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2.  The Language Tag

   Language tags are used to help identify languages, whether spoken,
   written, signed, or otherwise signaled, for the purpose of
   communication.  This includes constructed and artificial languages,
   but excludes languages not intended primarily for human
   communication, such as programming languages.

2.1.  Syntax

   The language tag is composed of one or more parts, known as
   "subtags".  Each subtag consists of a sequence of alphanumeric
   characters.  Subtags are distinguished and separated from one another
   by a hyphen ("-", ABNF [RFC4234] %x2D).  A language tag consists of a
   "primary language" subtag and a (possibly empty) series of subsequent
   subtags, each of which refines or narrows the range of languages
   identified by the overall tag.

   Usually, each type of subtag is distinguished by length, position in
   the tag, and content: subtags can be recognized solely by these
   features.  The only exception to this is a fixed list of
   grandfathered tags registered under RFC 3066 [RFC3066].  This makes
   it possible to construct a parser that can extract and assign some
   semantic information to the subtags, even if the specific subtag
   values are not recognized.  Thus, a parser need not have an up-to-
   date copy (or any copy at all) of the subtag registry to perform most
   searching and matching operations.

   The syntax of the language tag in ABNF [RFC4234] is:

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   Language-Tag  = langtag
                 / privateuse             ; private use tag
                 / grandfathered          ; grandfathered registrations

   langtag       = (language
                    ["-" script]
                    ["-" region]
                    *("-" variant)
                    *("-" extension)
                    ["-" privateuse])

   language      = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code
                 / 4ALPHA                 ; reserved for future use
                 / 5*8ALPHA               ; registered language subtag

   extlang       = *3("-" 3ALPHA)         ; specific ISO 639-3 codes

   script        = 4ALPHA                 ; ISO 15924 code

   region        = 2ALPHA                 ; ISO 3166 code
                 / 3DIGIT                 ; UN M.49 code

   variant       = 5*8alphanum            ; registered variants
                 / (DIGIT 3alphanum)

   extension     = singleton 1*("-" (2*8alphanum))

   singleton     = "a"-"w" / "y"-"z" / "0"-"9"
                 ; Single alphanumerics; "x" reserved for private use
                 ; NOTE: ABNF is case-insensitive

   privateuse    = ("x") 1*("-" (1*8alphanum))

   grandfathered = langtag   ; well-formed grandfathered tags
                 / irregular ; grandfathered that don't match langtag

   irregular     = "en-GB-oed" / "i-ami" / "i-bnn" / "i-default"
                 / "i-enochian" / "i-hak" / "i-klingon" / "i-lux"
                 / "i-mingo" / "i-navajo" / "i-pwn" / "i-tao"
                 / "i-tay" / "i-tsu" / "sgn-BE-fr" / "sgn-BE-nl"
                 / "sgn-CH-de"

   alphanum      = (ALPHA / DIGIT)       ; letters and numbers

   Figure 1: Language Tag ABNF

   All subtags have a maximum length of eight characters and whitespace
   is not permitted in a language tag.  There is a subtlety in the ABNF

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   production 'variant': variants starting with a digit MAY be four
   characters long, while those starting with a letter MUST be at least
   five characters long.  For examples of language tags, see Appendix B.

   Note Well: the ABNF syntax does not distinguish between upper and
   lowercase.  The appearance of upper and lowercase letters in the
   varous ABNF productions above do not affect how implementations
   interpret tags.  That is, the tag "I-AMI" matches the item "i-ami" in
   the 'irregular' production.  At all times, 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 the subtags, but these MUST NOT be taken to carry meaning.

   For example:

   o  [ISO639-1] recommends that language codes be written in lowercase
      ('mn' Mongolian).

   o  [ISO3166-1] recommends that country codes be capitalized ('MN'
      Mongolia).

   o  [ISO15924] recommends that script codes use lowercase with the
      initial letter capitalized ('Cyrl' Cyrillic).

   However, in the tags defined by this document, the uppercase US-ASCII
   letters in the range 'A' through 'Z' are considered equivalent and
   mapped directly to their US-ASCII lowercase equivalents in the range
   'a' through 'z'.  Thus, the tag "mn-Cyrl-MN" is not distinct from
   "MN-cYRL-mn" or "mN-cYrL-Mn" (or any other combination), and each of
   these variations conveys the same meaning: Mongolian written in the
   Cyrillic script as used in Mongolia.

   Although case distinctions do not carry meaning in language tags,
   consistent formatting and presentation of the tags will aid users.
   The format of the tags and subtags in the registry is RECOMMENDED.
   In this format, all non-initial two-letter subtags are uppercase, all
   non-initial four-letter subtags are titlecase, and all other subtags
   are lowercase.

   Note that although [RFC4234] refers to octets, the language tags
   described in this document are sequences of characters from the US-
   ASCII [ISO646] repertoire.  Language tags MAY be used in documents
   and applications that use other encodings, so long as these encompass
   the US-ASCII repertoire.  An example of this would be an XML document
   that uses the UTF-16LE [RFC2781] encoding of [Unicode].

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2.2.  Language Subtag Sources and Interpretation

   The namespace of language tags and their subtags is administered by
   the Internet Assigned Numbers Authority (IANA) [RFC2860] according to
   the rules in Section 5 of this document.  The Language Subtag
   Registry maintained by IANA is the source for valid subtags: other
   standards referenced in this section provide the source material for
   that registry.

   Terminology used in this document:

   o  Tag or tags refers to a complete language tag, such as
      "sr-Latn-RS" or "az-Arab-IR".  Examples of tags in this document
      are enclosed in double-quotes ("en-US").

   o  Subtag refers to a specific section of a tag, delimited by hyphen,
      such as the subtag 'Hant' in "zh-Hant-CN".  Examples of subtags in
      this document are enclosed in single quotes ('Hant').

   o  Code or codes refers to values defined in external standards (and
      which are used as subtags in this document).  For example, 'Hant'
      is an [ISO15924] script code that was used to define the 'Hant'
      script subtag for use in a language tag.  Examples of codes in
      this document are enclosed in single quotes ('en', 'Hant').

   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 2.2.8.

   Language tags are designed so that each subtag type has unique length
   and content restrictions.  These 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.

   Subtags in the IANA registry that do not come from an underlying
   standard can only appear in specific positions in a tag.
   Specifically, they can only occur as primary language subtags or as
   variant subtags.

   Note that sequences of private use and extension subtags MUST occur
   at the end of the sequence of subtags and MUST NOT be interspersed
   with subtags defined elsewhere in this document.

   Single-letter and single-digit subtags are reserved for current or
   future use.  These include the following current uses:

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   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 3.7.

   The single-letter subtag 'i' is used by some grandfathered tags, such
   as "i-default", where it always appears in the first position and
   cannot be confused with an extension.

2.2.1.  Primary Language Subtag

   The primary language subtag is the first subtag in a language tag
   (with the exception of private use and certain grandfathered tags)
   and cannot be omitted.  The following rules apply to the primary
   language subtag:

   1.  All two-character primary language subtags were defined in the
       IANA registry according to the assignments found in the standard
       ISO 639 Part 1, "ISO 639-1:2002, Codes for the representation of
       names of languages -- Part 1: Alpha-2 code" [ISO639-1], or using
       assignments subsequently made by the ISO 639-1 registration
       authority (RA) or governing standardization bodies.

   2.  All three-character primary language subtags were defined in the
       IANA registry according to the assignments found in either ISO
       639 Part 2, "ISO 639-2:1998 - Codes for the representation of
       names of languages -- Part 2: Alpha-3 code - edition 1"
       [ISO639-2], ISO 639 Part 3, "ISO 639-3:200?, [[??missing official
       title??]]", or assignments subsequently made by the relevant ISO
       639 registration authorities or governing standardization bodies.

   3.  The subtags in the range 'qaa' through 'qtz' are reserved for
       private use in language tags.  These subtags correspond to codes
       reserved by ISO 639-2 for private use.  These codes MAY be used
       for non-registered primary language subtags (instead of using
       private use subtags following 'x-').  Please refer to Section 4.5
       for more information on private use subtags.

   4.  All four-character language subtags are reserved for possible
       future standardization.

   5.  All language subtags of 5 to 8 characters in length in the IANA
       registry were defined via the registration process in Section 3.5

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       and MAY 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 proposals rejected by ISO 639/RA will be closely
       scrutinized before they are registered with IANA.

   6.  The single-character subtag 'x' as the primary subtag indicates
       that the language tag consists solely of subtags whose meaning is
       defined by private agreement.  For example, in the tag "x-fr-CH",
       the subtags 'fr' and 'CH' SHOULD NOT be taken to represent the
       French language or the country of Switzerland (or any other value
       in the IANA registry) unless there is a private agreement in
       place to do so.  See Section 4.5.

   7.  The single-character subtag 'i' is used by some grandfathered
       tags (see Section 2.2.8) such as "i-klingon" and "i-bnn".  (Other
       grandfathered tags have a primary language subtag in their first
       position.)

   8.  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 two-character code
   and a three character code assigned by either ISO 639-2 or ISO 693-3,
   only the ISO 639-1 two-character code is defined in the IANA
   registry.

   Note: For languages that have no ISO 639-1 two-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 in
   the IANA registry.  At the time this document was created, all
   languages that had both kinds of three-character code were also
   assigned a two-character code; it is expected that future assignments
   of this nature will not occur.

   Note: To avoid problems with versioning and subtag choice as
   experienced during the transition between RFC 1766 and RFC 3066, as
   well as the canonical nature of subtags defined by this document, the
   ISO 639 Registration Authority Joint Advisory Committee (ISO 639/
   RA-JAC) has included the following statement in [iso639.prin]:

      "A language code already in ISO 639-2 at the point of freezing ISO
      639-1 shall not later be added to ISO 639-1.  This is to ensure
      consistency in usage over time, since users are directed in
      Internet applications to employ the alpha-3 code when an alpha-2
      code for that language is not available."

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   In order to avoid instability in the canonical form of tags, if a
   two-character code is added to ISO 639-1 for a language for which a
   three-character code was already included in either ISO 639-2 or ISO
   639-3, the two-character code MUST NOT be registered.  See
   Section 3.4.

   For example, if some content were tagged with 'haw' (Hawaiian), which
   currently has no two-character code, the tag would not be invalidated
   if ISO 639-1 were to assign a two-character code to the Hawaiian
   language at a later date.

   Note: An example of independent primary language subtag registration
   might include: one of the grandfathered IANA registrations is
   "i-enochian".  The subtag 'enochian' could be registered in the IANA
   registry 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.

2.2.2.  Extended Language Subtags

   Extended language subtags are used to identify languages or dialects
   that are subdivisions within another language.  Such an enclosing
   language is sometimes called a "collective" or "macro" language.  The
   following rules apply to the extended language subtags:

   1.  These subtags were defined in the IANA registry according to
       assignments found in ISO 639 Part 3.

   2.  A sequence of up to three extended language subtags MAY appear in
       a language tag.  This sequence MUST follow the primary language
       subtag and precede any other subtags.

   3.  Each extended language subtag MUST only be used with the exact
       sequence of subtags that appears in the 'Prefix' field in its
       registry record.

   4.  There MAY be up to three extended language subtags.

   5.  Other values MUST NOT be assigned to the extended language subtag
       except by revision or update of this document.

   Extended language subtag records MUST include exactly one 'Prefix'
   field indicating an appropriate subtag or sequence of subtags for
   that extended language subtag.

   For example, the 'gan' subtag, representing the 'Gan' dialect of
   Chinese, has a prefix of "zh" in its registry record.  The 'cmn'
   subtag, representing the 'Mandarin' dialect of Chinese has the same

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   prefix.  Thus, the tags "zh-gan-Hant" or "zh-cmn-CN" are appropriate,
   while the tag "zh-cmn-gan" is not.

   Now suppose that 'xxx' is a subtag that represents a dialect of
   'Gan'.  It would have a 'Prefix' field of "zh-gan", making the tag
   "zh-gan-xxx" appropriate, while the tags "zh-xxx" and "zh-xxx-gan"
   would not be appropriate.

2.2.3.  Script Subtag

   Script subtags are used to indicate the script or writing system
   variations that distinguish the written forms of a language or its
   dialects.  The following rules apply to the script subtags:

   1.  All four-character subtags were defined according to
       [ISO15924]--"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.

   2.  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.

   3.  The script subtags 'Qaaa' through 'Qabx' are reserved for private
       use in language tags.  These subtags correspond to codes reserved
       by ISO 15924 for private use.  These codes MAY be used for non-
       registered script values.  Please refer to Section 4.5 for more
       information on private use subtags.

   4.  Script subtags MUST NOT be registered using the process in
       Section 3.5 of this document.  Variant subtags MAY be considered
       for registration for that purpose.

   5.  There MUST be at most one script subtag in a language tag, and
       the script subtag SHOULD be omitted when it adds no
       distinguishing value to the tag or when the primary language
       subtag's record includes a Suppress-Script field listing the
       applicable script subtag.

   Example: "sr-Latn" represents Serbian written using the Latin script.

2.2.4.  Region Subtag

   Region subtags are used to indicate linguistic variations associated
   with or appropriate to a specific country, territory, or region.
   Typically, a region subtag is used to indicate regional dialects or

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   usage, or region-specific spelling conventions.  A region subtag can
   also be used to indicate that content is expressed in a way that is
   appropriate for use throughout a region, for instance, Spanish
   content tailored to be useful throughout Latin America.

   The following rules apply to the region subtags:

   1.  Region subtags MUST follow any language, extended language, or
       script subtags and MUST precede all other subtags.

   2.  All two-character subtags following the primary subtag were
       defined in the IANA registry according to the assignments found
       in [ISO3166-1] ("Codes for the representation of names of
       countries and their subdivisions -- Part 1: Country codes") using
       the list of alpha-2 country codes, or using assignments
       subsequently made by the ISO 3166 maintenance agency or governing
       standardization bodies.

   3.  All three-character subtags consisting of digit (numeric)
       characters following the primary subtag were defined in the IANA
       registry according to the assignments found in UN Standard
       Country or Area Codes for Statistical Use [UN_M.49] or
       assignments subsequently made by the governing standards body.
       Note that not all of the UN M.49 codes are defined in the IANA
       registry.  The following rules define which codes are entered
       into the registry as valid subtags:

       A.  UN numeric codes assigned to 'macro-geographical
           (continental)' or sub-regions MUST be registered in the
           registry.  These codes are not associated with an assigned
           ISO 3166 alpha-2 code and represent supra-national areas,
           usually covering more than one nation, state, province, or
           territory.

       B.  UN numeric codes for 'economic groupings' or 'other
           groupings' MUST NOT be registered in the IANA registry and
           MUST NOT be used to form language tags.

       C.  UN numeric codes for countries or areas with ambiguous ISO
           3166 alpha-2 codes, when entered into the registry, MUST be
           defined according to the rules in Section 3.4 and MUST be
           used to form language tags that represent the country or
           region for which they are defined.

       D.  UN numeric codes for countries or areas for which there is an
           associated ISO 3166 alpha-2 code in the registry MUST NOT be
           entered into the registry and MUST NOT be used to form
           language tags.  Note that the ISO 3166-based subtag in the

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           registry MUST actually be associated with the UN M.49 code in
           question.

       E.  UN numeric codes and ISO 3166 alpha-2 codes for countries or
           areas listed as eligible for registration in [RFC4645] but
           not presently registered MAY be entered into the IANA
           registry via the process described in Section 3.5.  Once
           registered, these codes MAY be used to form language tags.

       F.  All other UN numeric codes for countries or areas that do not
           have an associated ISO 3166 alpha-2 code MUST NOT be entered
           into the registry and MUST NOT be used to form language tags.
           For more information about these codes, see Section 3.4.

   4.  Note: The alphanumeric codes in Appendix X of the UN document
       MUST NOT be entered into the registry and MUST NOT be used to
       form language tags.  (At the time this document was created,
       these values matched the ISO 3166 alpha-2 codes.)

   5.  There MUST be at most one region subtag in a language tag and the
       region subtag MAY be omitted, as when it adds no distinguishing
       value to the tag.

   6.  The region 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 MAY be used for private use region subtags (instead of
       using a private use subtag sequence).  Please refer to
       Section 4.5 for more information on private use subtags.

   "de-CH" represents German ('de') as used in Switzerland ('CH').

   "sr-Latn-RS" represents Serbian ('sr') written using Latin script
   ('Latn') as used in Serbia ('RS').

   "es-419" represents Spanish ('es') appropriate to the UN-defined
   Latin America and Caribbean region ('419').

2.2.5.  Variant Subtags

   Variant subtags are used to indicate additional, well-recognized
   variations that define a language or its dialects that are not
   covered by other available subtags.  The following rules apply to the
   variant subtags:

   1.  Variant subtags are not associated with any external standard.
       Variant subtags and their meanings are defined by the
       registration process defined in Section 3.5.

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   2.  Variant subtags MUST follow all of the other defined subtags, but
       precede any extension or private use subtag sequences.

   3.  More than one variant MAY be used to form the language tag.

   4.  Variant subtags MUST be registered with IANA according to the
       rules in Section 3.5 of this document before being used to form
       language tags.  In order to distinguish variants from other types
       of subtags, registrations MUST meet the following length and
       content restrictions:

       1.  Variant subtags that begin with a letter (a-z, A-Z) MUST be
           at least five characters long.

       2.  Variant subtags that begin with a digit (0-9) MUST be at
           least four characters long.

   Variant subtag records in the language subtag registry MAY include
   one or more 'Prefix' fields, which indicate the language tag or tags
   that would make a suitable prefix (with other subtags, as
   appropriate) in forming a language tag with the variant.  For
   example, the subtag 'nedis' has a Prefix of "sl", making it suitable
   to form language tags such as "sl-nedis" and "sl-IT-nedis", but not
   suitable for use in a tag such as "zh-nedis" or "it-IT-nedis".

   "sl-nedis" represents the Natisone or Nadiza dialect of Slovenian.

   "de-CH-1996" represents German as used in Switzerland and as written
   using the spelling reform beginning in the year 1996 C.E.

   Most variants that share a prefix are mutually exclusive.  For
   example, the German orthographic variations '1996' and '1901' SHOULD
   NOT be used in the same tag, as they represent the dates of different
   spelling reforms.  A variant that can meaningfully be used in
   combination with another variant SHOULD include a 'Prefix' field in
   its registry record that lists that other variant.  For example, if
   another German variant 'example' were created that made sense to use
   with '1996', then 'example' should include two Prefix fields: "de"
   and "de-1996".

2.2.6.  Extension Subtags

   Extensions provide a mechanism for extending language tags for use in
   various applications.  See Section 3.7.  The following rules apply to
   extensions:

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   1.   Extension subtags are separated from the other subtags defined
        in this document by a single-character subtag ("singleton").
        The singleton MUST be one allocated to a registration authority
        via the mechanism described in Section 3.7 and MUST NOT be the
        letter 'x', which is reserved for private use subtag sequences.

   2.   Note: Private use subtag sequences starting with the singleton
        subtag 'x' are described in Section 2.2.7 below.

   3.   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, "a-value" is not a well-formed language tag,
        while "de-a-value" is.

   4.   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.  Note that
        the tag "en-a-bbb-x-a-ccc" is valid because the second
        appearance of the singleton 'a' is in a private use sequence.

   5.   Extension subtags MUST meet all of the requirements for the
        content and format of subtags defined in this document.

   6.   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.

   7.   Each extension subtag MUST be from two to eight characters long
        and consist solely of letters or digits, with each subtag
        separated by a single '-'.

   8.   Each singleton MUST be followed by at least one extension
        subtag.  For example, the tag "tlh-a-b-foo" is invalid because
        the first singleton 'a' is followed immediately by another
        singleton 'b'.

   9.   Extension subtags MUST follow all language, extended language,
        script, region, and variant subtags in a tag.

   10.  All subtags following the singleton and before another singleton
        are part of the extension.  Example: In the tag "fr-a-Latn", the
        subtag 'Latn' does not represent the script subtag 'Latn'
        defined in the IANA Language Subtag Registry.  Its meaning is
        defined by the extension 'a'.

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   11.  In the event that more than one extension appears in a single
        tag, the tag SHOULD be canonicalized as described in
        Section 4.4.

   For example, if the prefix singleton 'r' and the shown subtags were
   defined, then the following tag would be a valid example: "en-Latn-
   GB-boont-r-extended-sequence-x-private"

2.2.7.  Private Use Subtags

   Private use subtags are used to indicate distinctions in language
   important in a given context by private agreement.  The following
   rules apply to private use subtags:

   1.  Private use subtags are separated from the other subtags defined
       in this document by the reserved single-character subtag 'x'.

   2.  Private use subtags MUST conform to the format and content
       constraints defined in the ABNF for all subtags.

   3.  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.

   4.  A tag MAY consist entirely of private use subtags.

   5.  No source is defined for private use subtags.  Use of private use
       subtags is by private agreement only.

   6.  Private use subtags are NOT RECOMMENDED where alternatives exist
       or for general interchange.  See Section 4.5 for more information
       on private use subtag choice.

   For example: Users who wished to utilize codes from the Ethnologue
   publication of SIL International for language 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'.

2.2.8.  Grandfathered Registrations

   Prior to RFC 4646, whole language tags were registered according to
   the rules in RFC 1766 and/or RFC 3066.  These registered tags
   maintain their validity.  Of those tags, those that were made
   obsolete or redundant by the advent of RFC 4646 or by subsequent
   registration of subtags are maintained in the registry in records as

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   "redundant" tag records.  Those tags that would not be well-formed
   according to the ABNF in this document or that contain subtags that
   do not individually appear in the registry are maintained in the
   registry in records of the "grandfathered" type.

   Grandfathered tags contain one or more subtags that are not defined
   in the Language Subtag Registry (see Section 3).  Redundant tags
   consist entirely of subtags defined above and whose independent
   registration was superseded by [RFC4646].  For more information see
   Section 3.8.

   Some grandfathered tags are "regular" in that they match the
   'langtag' production in Figure 1.  In some cases, these tags could
   become redundant if their (current unregistered) subtags were to be
   registered (as variants, for example).  In other cases, although the
   subtags match the language tag pattern, the meaning assigned to the
   various subtags is prohibited by rules elsewhere in this document.
   Those tags can never become redundant.

   The remaining grandfathered tags are "irregular" and do not match the
   'langtag' production.  These are listed in the 'irregular' production
   in Figure 1.  These grandfathered tags can never become redundant.
   Many of these tags have been superseded by other registrations: their
   record contains a Preferred-Value field that really ought to be used
   to form language tags representing that value.

2.2.9.  Classes of Conformance

   Implementations sometimes need to describe their capabilities with
   regard to the rules and practices described in this document.  There
   are two classes of conforming implementations described by this
   document: "well-formed" processors and "validating" processors.
   Claims of conformance SHOULD explicitly reference one of these
   definitions.

   An implementation of "well-formed" checking of language tags MUST
   check that the tag and all of its subtags, including extension and
   private use subtags, conform to the ABNF.  Note that irregular
   grandfathered tags are now listed in the 'irregular' production.

   An implementation of "well-formed" checking SHOULD 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 canonicalization
   rules contained in Section 4.4.

   An implementation that claims to be validating MUST:

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   o  Check that the tag is well-formed.

   o  Check that singletone subtags that identify extensions do not
      repeat.

   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 3.7
      are supported, including version, revision, and date.

   o  For any such extensions supported, check that all subtags used in
      that extension are valid.

   o  For extended language subtags, check that the tag matches the
      'Prefix' field associated with the subtag.  The tag matches if the
      'Prefix' exactly matches the start of the tag.  For example, the
      prefix "sgn-ase" matches the tag "sgn-ase-US" but does not match
      the tag "sgn-bvs-ase-US".

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3.  Registry Format and Maintenance

   This section defines the Language Subtag Registry and the maintenance
   and update procedures associated with it, as well as a registry for
   extensions to language tags (Section 3.7).

   The Language Subtag Registry contains a comprehensive list of all of
   the subtags valid in language tags.  This allows implementers a
   straightforward and reliable way to validate language tags.  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 successors.  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.)

3.1.  Format of the IANA Language Subtag Registry

   The IANA Language Subtag Registry ("the registry") consists of a text
   file that is machine readable in the format described in this
   section, plus copies of the registration forms approved in accordance
   with the process described in Section 3.5.  The existing registration
   forms for grandfathered and redundant tags taken from RFC 3066 will
   be maintained as part of the obsolete RFC 3066 registry.  The
   remaining set of initial subtags will not have registration forms
   created for them.

3.1.1.  File Format

   The registry is in the text format described below.  This format was
   based on the record-jar format described in [record-jar].

   Each line of text is limited to 72 characters, including all
   whitespace.  Records are separated by lines containing only the
   sequence "%%" (%x25.25).

   Each field can be viewed as a single, logical line of ASCII
   characters, comprising a field-name and a field-body separated by a
   COLON character (%x3A).  For convenience, the field-body portion of
   this conceptual entity can be split into a multiple-line
   representation; this is called "folding".  The format of the registry
   is described by the following ABNF (per [RFC4234]):

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   registry   = record *("%%" CRLF record)
   record     = 1*( field-name *SP ":" *SP field-body CRLF )
   field-name = (ALPHA / DIGIT) [*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)]
   field-body = *(ASCCHAR/LWSP)
   ASCCHAR    = %x21-25 / %x27-7E / UNICHAR ; Note: AMPERSAND is %x26
   UNICHAR    = "&#x" 2*6HEXDIG ";"

   Figure 2: Registry Format ABNF

   The sequence '..' (%x2E.2E) in a field-body denotes a range of
   values.  Such a range represents all subtags of the same length that
   are in alphabetic or numeric order within that range, including the
   values explicitly mentioned.  For example 'a..c' denotes the values
   'a', 'b', and 'c' and '11..13' denotes the values '11', '12', and
   '13'.

   Characters from outside the US-ASCII [ISO646] repertoire, as well as
   the AMPERSAND character ("&", %x26) when it occurs in a field-body,
   are represented by a "Numeric Character Reference" using hexadecimal
   notation in the style used by [XML10] (see
   <http://www.w3.org/TR/REC-xml/#dt-charref>).  This consists of the
   sequence "&#x" (%x26.23.78) followed by a hexadecimal representation
   of the character's code point in [ISO10646] followed by a closing
   semicolon (%x3B).  For example, the EURO SIGN, U+20AC, would be
   represented by the sequence "&#x20AC;".  Note that the hexadecimal
   notation MAY have between two and six digits.

   All fields whose field-body contains a date value use the "full-date"
   format specified in [RFC3339].  For example: "2004-06-28" represents
   June 28, 2004, in the Gregorian calendar.

3.1.2.  Record Definitions

   There are three types of records in the registry: "File-Date",
   "Subtag", and "Tag" records.

   The first record in the registry is a "File-Date" record.  This
   record contains the single field whose field-name is "File-Date" (see
   Figure 2).  The field-body of this record contains the last
   modification date of this copy of the registry, making it possible to
   compare different versions of the registry.  The registry on the IANA
   website is the most current.  Versions with an older date than that
   one are not up-to-date.

   File-Date: 2004-06-28
   %%

   Figure 3: Example of the File-Date Record

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   Subsequent records represent either subtags or tags in the registry.
   "Subtag" records contain a field with a field-name of "Subtag",
   while, unsurprisingly, "Tag" records contain a field with a field-
   name of "Tag".  Each of the fields in each record MUST occur no more
   than once, unless otherwise noted below.  Each record MUST contain
   the following fields:

   o  'Type'

      *  Type's field-body MUST consist of one of the following strings:
         "language", "extlang", "script", "region", "variant",
         "grandfathered", and "redundant" and denotes the type of tag or
         subtag.

   o  Either 'Subtag' or 'Tag'

      *  Subtag's field-body contains the subtag being defined.  This
         field MUST only appear in records of whose 'Type' has one of
         these values: "language", "extlang", "script", "region", or
         "variant".

      *  Tag's field-body contains a complete language tag.  This field
         MUST only appear in records whose 'Type' has one of these
         values: "grandfathered" or "redundant".  Note that the field-
         body will always follow the 'grandfathered' production in the
         ABNF in Section 2.1

   o  Description

      *  Description's field-body contains a non-normative description
         of the subtag or tag.

   o  Added

      *  Added's field-body contains the date the record was added to
         the registry.

   Each record MAY also contain the following fields:

   o  Preferred-Value

      *  For fields of type 'script', 'region', and 'variant',
         'Preferred-Value' contains the subtag of the same 'Type' that
         is preferred for forming the language tag.

      *  For fields of type 'language' and 'extlang', 'Preferred-Value'
         contains the language production (see Figure 1) that is
         preferred when forming the language tag.  This can be simply a

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         'language' subtag, or it can be a 'language' subtag followed by
         an extended language sequence.

      *  For fields of type 'grandfathered' and 'redundant', a canonical
         mapping to a complete language tag.

   o  Deprecated

      *  Deprecated's field-body contains the date the record was
         deprecated.

   o  Prefix

      *  Prefix's field-body contains a language tag with which this
         subtag MAY be used to form a new language tag, perhaps with
         other subtags as well.  This field MUST only appear in records
         whose 'Type' field-body is 'variant' or 'extlang'.  For
         example, the 'Prefix' for the variant 'nedis' is 'sl', meaning
         that the tags "sl-nedis" and "sl-IT-nedis" might be appropriate
         while the tag "is-nedis" is not.

   o  Comments

      *  Comments contains additional information about the subtag, as
         deemed appropriate for understanding the registry and
         implementing language tags using the subtag or tag.

   o  Suppress-Script

      *  Suppress-Script contains a script subtag that SHOULD NOT be
         used to form language tags with the associated primary language
         subtag.  This field MUST only appear in records whose 'Type'
         field-body is 'language'.  See Section 4.1.

   Future versions of this document might add additional fields to the
   registry, so implementations SHOULD ignore fields found in the
   registry that are not defined in this document.

3.1.3.  Subtag and Tag Fields

   The 'Subtag' field MUST use lowercase letters to form the subtag,
   with two exceptions.  Subtags whose 'Type' field is 'script' (in
   other words, subtags defined by ISO 15924) MUST use titlecase.
   Subtags whose 'Type' field is 'region' (in other words, subtags
   defined by ISO 3166) MUST use uppercase.  These exceptions mirror the
   use of case in the underlying standards.

   Each subtag in the tags contained in a 'Tag' field MUST be formatted

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   using the rules in the preceeding paragraph.  That is, all subtags
   are lowercase except for subtags that represent script or region
   codes.

3.1.4.  Description Field

   The field 'Description' contains a description of the tag or subtag
   in the record.  The 'Description' field MAY appear more than once per
   record, that is, there can be multiple descriptions for a given
   record.  At least one of the 'Description' fields MUST be written or
   transcribed into the Latin script; additional 'Description' fields
   MAY also include a description in a non-Latin script.  Each
   'Description' field MUST be unique, both within the record in which
   it appears and for the collection of records of the same type.
   Moreover, formatting variations of the same description MUST NOT
   occur in that specific record or in any other record of the same
   type.  For example, while the ISO 639-1 code 'fy' contains both the
   descriptions "Western Frisian" and "Frisian, Western", only one of
   these descriptions appears in the registry.

   The 'Description' field is used for identification purposes and
   SHOULD NOT be taken to represent the actual native name of the
   language or variation or to be in any particular language.

   For records taken from a source standard (such as ISO 639 or ISO
   3166), the 'Description' value(s) SHOULD also be taken from the
   source standard.  Multiple descriptions in the source standard MUST
   be split into separate 'Description' fields.  The source standard's
   descriptions MAY be edited, either prior to insertion or via the
   registration process.  For fields of type 'language' or 'extlang',
   the first 'Description' field appearing in the Registry corresponds
   to the Reference Name assigned by ISO 639-3.  This helps facilitate
   cross-referencing between ISO 639 and the registry.

   When creating or updating a record due to the action of one of the
   source standards, the Language Subtag Reviewer SHOULD remove
   duplicate or redundant descriptions and MAY edit descriptions to
   correct irregularities in formatting prior to submitting the proposed
   record to the ietf-languages list.

   Note: Descriptions in registry entries that correspond to ISO 639,
   ISO 15924, ISO 3166, or UN M.49 codes are intended only to indicate
   the meaning of that identifier as defined in the source standard at
   the time it was added to the registry.  The description does not
   replace the content of the source standard itself.  The descriptions
   are not intended to be the English localized names for the subtags.
   Localization or translation of language tag and subtag descriptions
   is out of scope of this document.

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3.1.5.  Deprecated Field

   The field 'Deprecated' MAY be added to any record via the maintenance
   process described in Section 3.3 or via the registration process
   described in Section 3.5.  Usually, the addition of a 'Deprecated'
   field is due to the action of one of the standards bodies, such as
   ISO 3166, withdrawing a code.  In some historical cases, it might not
   have been possible to reconstruct the original deprecation date.  For
   these cases, an approximate date appears in the registry.  Although
   valid in language tags, subtags and tags with a 'Deprecated' field
   are deprecated and validating processors SHOULD NOT generate these
   subtags.  Note that a record that contains a 'Deprecated' field and
   no corresponding 'Preferred-Value' field has no replacement mapping.

3.1.6.  Preferred-Value Field

   The field 'Preferred-Value' contains a mapping between the record in
   which it appears and another tag or subtag.  The value in this field
   is strongly RECOMMENDED as the best choice to represent the value of
   this record when selecting a language tag.  These values form three
   groups:

   1.  ISO 639 language codes that were later withdrawn in favor of
       other codes.  These values are mostly a historical curiosity.

   2.  ISO 3166 region codes that have been withdrawn in favor of a new
       code.  This sometimes happens when a country changes its name or
       administration in such a way that warrants a new region code.

   3.  Grandfathered or redundant tags from RFC 3066.  In many cases,
       these tags have become obsolete because the values they represent
       were later encoded by ISO 639.

   Records that contain a 'Preferred-Value' field MUST also have a
   'Deprecated' field.  This field contains a date of deprecation.
   Thus, a language tag processor can use the registry to construct the
   valid, non-deprecated set of subtags for a given date.  In addition,
   for any given tag, a processor can construct the set of valid
   language tags that correspond to that tag for all dates up to the
   date of the registry.  The ability to do these mappings MAY be
   beneficial to applications that are matching, selecting, for
   filtering content based on its language tags.

   Note that 'Preferred-Value' mappings in records of type 'region'
   sometimes do not represent exactly the same meaning as the original
   value.  There are many reasons for a country code to be changed, and
   the effect this has on the formation of language tags will depend on
   the nature of the change in question.

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   In particular, the 'Preferred-Value' field does not imply retagging
   content that uses the affected subtag.

   The field 'Preferred-Value' MUST NOT be modified once created in the
   registry.  The field MAY be added to records according to the rules
   in Section 3.3.

   The 'Preferred-Value' field in records of type "grandfathered" and
   "redundant" contains whole language tags that are strongly
   RECOMMENDED for use in place of the record's value.  In many cases,
   the mappings were created by deprecation of the tags during the
   period before this document was adopted.  For example, the tag "no-
   nyn" was deprecated in favor of the ISO 639-1-defined language code
   'nn'.

3.1.7.  Prefix Field

   The field of type 'Prefix' MUST NOT be removed from any record.  The
   field-body for this type of field MUST NOT be modified.

   The field-body of the 'Prefix' field consists of a language tag whose
   subtags are appropriate to use with this subtag.  For example, the
   variant subtag '1996' has a 'Prefix' field of "de".  This means that
   tags starting with the sequence "de-" are appropriate with this
   subtag, so "de-Latg-1996" and "de-CH-1996" are both acceptable, while
   the tag "fr-1996" is an inappropriate choice.

   Records of type 'variant' MAY have more than one field of type
   'Prefix'.  Additional fields of this type MAY be added to a 'variant'
   record via the registration process.

   Records of type 'extlang' MUST have _exactly_ one 'Prefix' field.

3.1.8.  Comments Field

   The field 'Comments' MAY appear more than once per record.  This
   field MAY be inserted or changed via the registration process and no
   guarantee of stability is provided.  The content of this field is not
   restricted, except by the need to register the information, the
   suitability of the request, and by reasonable practical size
   limitations.

3.1.9.  Suppress-Script Field

   The field 'Suppress-Script' MUST only appear in records whose 'Type'
   field-body is 'language'.  This field MUST NOT appear more than one
   time in a record.  This field indicates a script used to write the
   overwhelming majority of documents for the given language and that

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   therefore adds no distinguishing information to a language tag.  It
   helps ensure greater compatibility between the language tags
   generated according to the rules in this document and language tags
   and tag processors or consumers based on RFC 3066.  For example,
   virtually all Icelandic documents are written in the Latin script,
   making the subtag 'Latn' redundant in the tag "is-Latn".

3.2.  Language Subtag Reviewer

   The Language Subtag Reviewer is appointed by the IESG for an
   indefinite term, subject to removal or replacement at the IESG's
   discretion.  The Language Subtag Reviewer moderates the ietf-
   languages mailing list, responds to requests for registration, and
   performs the other registry maintenance duties described in
   Section 3.3.  Only the Language Subtag Reviewer is permitted to
   request IANA to change, update, or add records to the Language Subtag
   Registry.  The Language Subtag Reviewer MAY delegate list moderation
   and other clerical duties as needed.

   The performance or decisions of the Language Subtag Reviewer MAY be
   appealed to the IESG under the same rules as other IETF decisions
   (see [RFC2026]).  The IESG can reverse or overturn the decision of
   the Language Subtag Reviewer, provide guidance, or take other
   appropriate actions.

3.3.  Maintenance of the Registry

   Maintenance of the registry requires that as codes are assigned or
   withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language
   Subtag Reviewer MUST evaluate each change, determine whether it
   conflicts with existing registry entries, and submit the information
   to IANA for inclusion in the registry.  If a change takes place and
   the Language Subtag Reviewer does not do this in a timely manner,
   then any interested party MAY use the procedure in Section 3.5 to
   register the appropriate update.

   Note: The redundant and grandfathered entries together are the
   complete list of tags registered under [RFC3066].  The redundant tags
   are those that can now be formed using the subtags defined in the
   registry together with the rules of Section 2.2.  The grandfathered
   entries include those that can never be legal under those same
   provisions plus those tags that contain subtags not yet registered
   or, perhaps, inappropriate for registration.

   The set of redundant and grandfathered tags is permanent and stable:
   new entries in this section MUST NOT be added and existing entries
   MUST NOT be removed.  Records of type 'grandfathered' MAY have their
   type converted to 'redundant'; see item 12 in Section 3.6 for more

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   information.  The decision-making process about which tags were
   initially grandfathered and which were made redundant is described in
   [RFC4645].

   RFC 3066 tags that were deprecated prior to the adoption of [RFC4646]
   are part of the list of grandfathered tags, and their component
   subtags were not included as registered variants (although they
   remain eligible for registration).  For example, the tag "art-lojban"
   was deprecated in favor of the language subtag 'jbo'.

   The Language Subtag Reviewer MUST ensure that new subtags meet the
   requirements in Section 4.1 or submit an appropriate alternate subtag
   as described in that section.  When either a change or addition to
   the registry is needed, the Language Subtag Reviewer MUST prepare the
   complete record, including all fields, and forward it to IANA for
   insertion into the registry.  Each record being modified or inserted
   MUST be forwarded in a separate message.

   If a record represents a new subtag that does not currently exist in
   the registry, then the message's subject line MUST include the word
   "INSERT".  If the record represents a change to an existing subtag,
   then the subject line of the message MUST include the word "MODIFY".
   The message MUST contain both the record for the subtag being
   inserted or modified and the new File-Date record.  Here is an
   example of what the body of the message might contain:

   LANGUAGE SUBTAG MODIFICATION
   File-Date: 2005-01-02
   %%
   Type: variant
   Subtag: nedis
   Description: Natisone dialect
   Description: Nadiza dialect
   Added: 2003-10-09
   Prefix: sl
   Comments: This is a comment shown
     as an example.
   %%

   Figure 4: Example of a Language Subtag Modification Form

   Whenever an entry is created or modified in the registry, the 'File-
   Date' record at the start of the registry is updated to reflect the
   most recent modification date in the [RFC3339] "full-date" format.

   Before forwarding a new registration to IANA, the Language Subtag
   Reviewer MUST ensure that values in the 'Subtag' field match case
   according to the description in Section 3.1.

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3.4.  Stability of IANA Registry Entries

   The stability of entries and their meaning in the registry is
   critical to the long-term stability of language tags.  The rules in
   this section guarantee that a specific language tag's meaning is
   stable over time and will not change.

   These rules specifically deal with how changes to codes (including
   withdrawal and deprecation of codes) maintained by ISO 639, ISO
   15924, ISO 3166, and UN M.49 are reflected in the IANA Language
   Subtag Registry.  Assignments to the IANA Language Subtag Registry
   MUST follow the following stability rules:

   1.   Values in the fields 'Type', 'Subtag', 'Tag', 'Added',
        'Deprecated' and 'Preferred-Value' MUST NOT be changed and are
        guaranteed to be stable over time.

   2.   Values in the 'Description' field MUST NOT be changed in a way
        that would invalidate previously-existing tags.  They MAY be
        broadened somewhat in scope, changed to add information, or
        adapted to the most common modern usage.  For example, countries
        occasionally change their official names; a historical example
        of this would be "Upper Volta" changing to "Burkina Faso".

   3.   Values in the field 'Prefix' MAY be added to records of type
        'variant' via the registration process.  If a prefix is added to
        a variant record, 'Comment' fields SHOULD be used to explain
        different usages with the various prefixes.

   4.   Values in the field 'Prefix' in records of type 'variant' MAY be
        modified, so long as the modifications broaden the set of
        prefixes.  That is, a prefix MAY be replaced by one of its own
        prefixes.  For example, the prefix "en-US" could be replaced by
        "en", but not by the prefixes "en-Latn", "fr", or "en-US-boont".
        If one of those prefixes were needed, a new Prefix SHOULD be
        registered.

   5.   Values in the field 'Prefix' in records of type 'extlang' MUST
        NOT be modified.

   6.   Values in the field 'Prefix' MUST NOT be removed.

   7.   The field 'Comments' MAY be added, changed, modified, or removed
        via the registration process or any of the processes or
        considerations described in this section.

   8.   The field 'Suppress-Script' MAY be added or removed via the
        registration process.

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   9.   Codes assigned by ISO 639-1 that do not conflict with existing
        two-letter primary language subtags and which have no
        corresponding three-letter primary or extended language subtags
        defined in the registry are entered into the IANA registry as
        new records of type 'language'.

   10.  Codes assigned by ISO 639-2 that do not conflict with existing
        three-letter primary or extended language subtags are entered
        into the IANA registry as new records of type 'language'.

   11.  Codes assigned by ISO 639-3 that do not conflict with existing
        three-letter primary or extended language subtags are entered
        into the IANA registry as new records.

        1.  Codes that have a defined "macro-language" mapping at the
            time of their registration MUST be entered into the registry
            as records of type 'extlang' with a 'Prefix' field
            containing the appropriate prefix tag.

        2.  Codes that represent sign languages MUST be entered into the
            registry as record of type 'extlang' with a 'Prefix' field
            that matches the Basic Language Range "sgn" (see Section
            3.3.1 "Basic Filtering" in [RFC4647]).

        3.  All other codes MUST be entered into the registry as records
            of type 'language'.

   12.  A record of type 'language' or 'extlang' MUST NOT be registered
        if there exists a record of either type with the same subtag
        value.  For example, if an 'extlang' subtag 'foo' exists in the
        registry, all attempts to register a 'language' subtag 'foo'
        will be rejected.

   13.  Codes assigned by ISO 15924 and ISO 3166 that do not conflict
        with existing subtags of the associated type and whose meaning
        is not the same as an existing subtag of the same type are
        entered into the IANA registry as new records.

   14.  Codes assigned by ISO 639, ISO 15924, or ISO 3166 that are
        withdrawn by their respective maintenance or registration
        authority remain valid in language tags.  A 'Deprecated' field
        containing the date of withdrawal MUST be added to the record.
        If a new record of the same type is added that represents a
        replacement value, then a 'Preferred-Value' field MAY also be
        added.  The registration process MAY be used to add comments
        about the withdrawal of the code by the respective standard.

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        Example The region code 'TL' was assigned to the country 'Timor-
           Leste', replacing the code 'TP' (which was assigned to 'East
           Timor' when it was under administration by Portugal).  The
           subtag 'TP' remains valid in language tags, but its record
           contains the a 'Preferred-Value' of 'TL' and its field
           'Deprecated' contains the date the new code was assigned
           ('2004-07-06').

   15.  Codes assigned by ISO 639, ISO 15924, or ISO 3166 that conflict
        with existing subtags of the associated type, including subtags
        that are deprecated, MUST NOT be entered into the registry.  The
        following additional considerations apply to subtag values that
        are reassigned:

        A.  For ISO 639 codes, if the newly assigned code's meaning is
            not represented by a subtag in the IANA registry, the
            Language Subtag Reviewer, as described in Section 3.5, SHALL
            prepare a proposal for entering in the IANA registry as soon
            as practical a registered language subtag as an alternate
            value for the new code.  The form of the registered language
            subtag will be at the discretion of the Language Subtag
            Reviewer and MUST conform to other restrictions on language
            subtags in this document.

        B.  For all subtags whose meaning is derived from an external
            standard (that is, by ISO 639, ISO 15924, ISO 3166, or UN
            M.49), if a new meaning is assigned to an existing code and
            the new meaning broadens the meaning of that code, then the
            meaning for the associated subtag MAY be changed to match.
            The meaning of a subtag MUST NOT be narrowed, however, as
            this can result in an unknown proportion of the existing
            uses of a subtag becoming invalid.  Note: ISO 639
            maintenance agency/registration authority (MA/RA) has
            adopted a similar stability policy.

        C.  For ISO 15924 codes, if the newly assigned code's meaning is
            not represented by a subtag in the IANA registry, the
            Language Subtag Reviewer, as described in Section 3.5, SHALL
            prepare a proposal for entering in the IANA registry as soon
            as practical a registered variant subtag as an alternate
            value for the new code.  The form of the registered variant
            subtag will be at the discretion of the Language Subtag
            Reviewer and MUST conform to other restrictions on variant
            subtags in this document.

        D.  For ISO 3166 codes, if the newly assigned code's meaning is
            associated with the same UN M.49 code as another 'region'
            subtag, then the existing region subtag remains as the

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            preferred value for that region and no new entry is created.
            A comment MAY be added to the existing region subtag
            indicating the relationship to the new ISO 3166 code.

        E.  For ISO 3166 codes, if the newly assigned code's meaning is
            associated with a UN M.49 code that is not represented by an
            existing region subtag, then the Language Subtag Reviewer,
            as described in Section 3.5, SHALL prepare a proposal for
            entering the appropriate UN M.49 country code as an entry in
            the IANA registry.

        F.  For ISO 3166 codes, if there is no associated UN numeric
            code, then the Language Subtag Reviewer SHALL petition the
            UN to create one.  If there is no response from the UN
            within ninety days of the request being sent, the Language
            Subtag Reviewer SHALL prepare a proposal for entering in the
            IANA registry as soon as practical a registered variant
            subtag as an alternate value for the new code.  The form of
            the registered variant subtag will be at the discretion of
            the Language Subtag Reviewer and MUST conform to other
            restrictions on variant subtags in this document.  This
            situation is very unlikely to ever occur.

   16.  UN M.49 has codes for both countries and areas (such as '276'
        for Germany) and geographical regions and sub-regions (such as
        '150' for Europe).  UN M.49 country or area codes for which
        there is no corresponding ISO 3166 code SHOULD NOT be
        registered, except as a surrogate for an ISO 3166 code that is
        blocked from registration by an existing subtag.  If such a code
        becomes necessary, then the registration authority for ISO 3166
        SHOULD first be petitioned to assign a code to the region.  If
        the petition for a code assignment by ISO 3166 is refused or not
        acted on in a timely manner, the registration process described
        in Section 3.5 MAY then be used to register the corresponding UN
        M.49 code.  This way, UN M.49 codes remain available as the
        value of last resort in cases where ISO 3166 reassigns a
        deprecated value in the registry.

   17.  Stability provisions apply to grandfathered tags with this
        exception: should it be possible to compose one of the
        grandfathered tags from registered subtags, then the field
        'Type' in that record is changed from 'grandfathered' to
        'redundant'.  Note that this will not affect language tags that
        match the grandfathered tag, since these tags will now match
        valid generative subtag sequences.  For example, this document
        caused the ISO 639-3 code 'gan', used in the redundant tag "zh-
        gan", to be registered as an extended language subtag.  The
        formerly-grandfathered tag "zh-gan" became a redundant tag as a

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        result (but existing content or implementations that use "zh-
        gan" remain valid).

3.5.  Registration Procedure for Subtags

   The procedure given here MUST be used by anyone who wants to use a
   subtag not currently in the IANA Language Subtag Registry.

   Only subtags of type 'language' and 'variant' will be considered for
   independent registration of new subtags.  Handling of subtags needed
   for stability and subtags necessary to keep the registry synchronized
   with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits
   defined by this document are described in Section 3.3.  Stability
   provisions are described in Section 3.4.

   This procedure MAY also be used to register or alter the information
   for the 'Description', 'Comments', 'Deprecated', 'Prefix', or
   'Suppress-Script' fields in a subtag's record as described in
   Section 3.4.  Changes to all other fields in the IANA registry are
   NOT permitted.

   Registering a new subtag or requesting modifications to an existing
   tag or subtag starts with the requester filling out the registration
   form reproduced below.  Note that each response is not limited in
   size so that the request can adequately describe the registration.
   The fields in the "Record Requested" section SHOULD follow the
   requirements in Section 3.1.

   LANGUAGE SUBTAG REGISTRATION FORM
   1. Name of requester:
   2. E-mail address of requester:
   3. Record Requested:

      Type:
      Subtag:
      Description:
      Prefix:
      Preferred-Value:
      Deprecated:
      Suppress-Script:
      Comments:

   4. Intended meaning of the subtag:
   5. Reference to published description
      of the language (book or article):
   6. Any other relevant information:

   Figure 5: The Language Subtag Registration Form

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   The subtag registration form MUST be sent to
   <[email-masked]> for a two-week review period before it can
   be submitted to IANA.  (This is an open list and can be joined by
   sending a request to <[email-masked]>.  The list can
   be hosted by IANA or by any third party at the request of IESG.)

   Variant subtags are usually registered for use with a particular
   range of language tags.  For example, the subtag 'rozaj' is intended
   for use with language tags that start with the primary language
   subtag "sl", since Resian is a dialect of Slovenian.  Thus, the
   subtag 'rozaj' would be appropriate in tags such as "sl-Latn-rozaj"
   or "sl-IT-rozaj".  This information is stored in the 'Prefix' field
   in the registry.  Variant registration requests SHOULD include at
   least one 'Prefix' field in the registration form.

   Extended language subtags MUST include exactly one 'Prefix' field.

   The 'Prefix' field for a given registered subtag exists in the IANA
   registry as a guide to usage.  Additional prefixes MAY be added by
   filing an additional registration form.  In that form, the "Any other
   relevant information:" field MUST indicate that it is the addition of
   a prefix.

   Requests to add a prefix to a variant subtag that imply a different
   semantic meaning will probably be rejected.  For example, a request
   to add the prefix "de" to the subtag 'nedis' so that the tag "de-
   nedis" represented some German dialect would be rejected.  The
   'nedis' subtag represents a particular Slovenian dialect and the
   additional registration would change the semantic meaning assigned to
   the subtag.  A separate subtag SHOULD be proposed instead.

   The 'Description' field MUST contain a description of the tag being
   registered written or transcribed into the Latin script; it MAY also
   include a description in a non-Latin script.  Non-ASCII characters
   MUST be escaped using the syntax described in Section 3.1.  The
   'Description' field is used for identification purposes and doesn't
   necessarily represent the actual native name of the language or
   variation or to be in any particular language.

   While the 'Description' field itself is not guaranteed to be stable
   and errata corrections MAY be undertaken from time to time, attempts
   to provide translations or transcriptions of entries in the registry
   itself will probably be frowned upon by the community or rejected
   outright, as changes of this nature have an impact on the provisions
   in Section 3.4.

   When the two-week period has passed, the Language Subtag Reviewer
   either forwards the record to be inserted or modified to

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   [email-masked] according to the procedure described in Section 3.3, or
   rejects the request because of significant objections raised on the
   list or due to problems with constraints in this document (which MUST
   be explicitly cited).  The Language Subtag Reviewer MAY also extend
   the review period in two-week increments to permit further
   discussion.  The Language Subtag Reviewer MUST indicate on the list
   whether the registration has been accepted, rejected, or extended
   following each two-week period.

   Note that the Language Subtag Reviewer MAY 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 Language Subtag Reviewer MAY be appealed to the
   IESG [RFC2028] under the same rules as other IETF decisions
   [RFC2026].

   All approved registration forms are available online in the directory
   http://www.iana.org/numbers.html under "languages".

   Updates or changes to existing records follow the same procedure as
   new registrations.  The Language Subtag Reviewer decides whether
   there is consensus to update the registration following the two week
   review period; normally, objections by the original registrant will
   carry extra weight in forming such a consensus.

   Registrations are permanent and stable.  Once registered, subtags
   will not be removed from the registry and will remain a valid way in
   which to specify a specific language or variant.

   Note: The purpose of the "Reference to published description" section
   in the registration form is to aid in verifying whether a language is
   registered or what language or language variation 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 Language 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.

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3.6.  Possibilities for Registration

   Possibilities for registration of subtags or information about
   subtags include:

   o  Primary language subtags for languages not listed in ISO 639 that
      are not variants of any listed or registered language MAY be
      registered.  At the time this document was created, there were no
      examples of this form of subtag.  Before attempting to register a
      language subtag, there MUST be an attempt to register the language
      with ISO 639.  Subtags MUST NOT be registered for languages
      defined by codes that exist in ISO 639-1, ISO 639-2, or ISO 639-3,
      or that are under consideration by the ISO 639 registration
      authorities, or that 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 as a primary language subtag 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 or historical usage,
      transliteration or other transformation, or distinguishing
      variation MAY be registered as variant subtags.  An example is the
      'rozaj' subtag (the Resian dialect of Slovenian).

   o  The addition or maintenance of fields (generally of an
      informational nature) in Tag or Subtag records as described in
      Section 3.1 and subject to the stability provisions in
      Section 3.4.  This includes descriptions, comments, deprecation
      and preferred values for obsolete or withdrawn codes, or the
      addition of script or extlang information to primary language
      subtags.

   o  The addition of records and related field value changes necessary
      to reflect assignments made by ISO 639, ISO 15924, ISO 3166, and
      UN M.49 as described in Section 3.4.

   Subtags proposed for registration that would cause all or part of a
   grandfathered tag to become redundant but whose meaning conflicts
   with or alters the meaning of the grandfathered tag MUST be rejected.

   This document leaves the decision on what subtags or changes to
   subtags are appropriate (or not) to the registration process
   described in Section 3.5.

   Note: four-character primary language subtags are reserved to allow

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   for the possibility of alpha4 codes in some future addition to the
   ISO 639 family of standards.

   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/iso639-2

   ISO 639-3 defines a maintenance agency for additions to and changes
   in the list of languages in ISO 639-3.  This agency is:

   SIL International
   ISO 639-3 Registrar
   7500 W. Camp Wisdom Rd.
   Dallas, TX 75236 USA
   Phone: +1 972 708 7400, ext. 2293 Fax: +1 972 708 7546
   Email: [email-masked]
   URL: http://www.sil.org/iso639-3

   The maintenance agency for ISO 3166 (country codes) is:

   ISO 3166 Maintenance Agency
   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

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   reached at:

   Statistical Services Branch
   Statistics Division
   United Nations, Room DC2-1620
   New York, NY 10017, USA

   Fax: +1-212-963-0623
   E-mail: [email-masked]
   URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm

3.7.  Extensions and Extensions Registry

   Extension subtags are those introduced by single-character subtags
   ("singletons") other than 'x'.  They are reserved for the generation
   of identifiers that contain a language component and are compatible
   with applications that understand language tags.

   The structure and form of extensions are defined by this document so
   that implementations can be created that are forward compatible with
   applications that might be created using singletons in the future.
   In addition, defining a mechanism for maintaining singletons will
   lend stability to this document by reducing the likely need for
   future revisions or updates.

   Single-character subtags are assigned by IANA using the "IETF
   Consensus" policy defined by [RFC2434].  This policy requires the
   development of an RFC, which SHALL define 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 or include each
   of the following:

   o  The specification MUST reference the specific version or revision
      of this document that governs 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 particular, it MUST
      specify that case is not significant and that subtags MUST NOT
      exceed eight characters in length.

   o  The specification MUST specify a canonical representation.

   o  The specification of valid subtags MUST be available over the
      Internet and at no cost.

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   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 specification, MUST NOT be retracted or change
      in meaning in any substantial way.

   o  The specification MUST include in a separate section the
      registration form reproduced in this section (below) to be used in
      registering the extension upon publication as an RFC.

   o  IANA MUST be informed of changes to the contact information and
      URL for the specification.

   IANA will maintain a registry of allocated single-character
   (singleton) subtags.  This registry MUST use the record-jar format
   described by the ABNF in Section 3.1.  Upon publication of an
   extension as an RFC, the maintaining authority defined in the RFC
   MUST forward this registration form to [email-masked], who MUST
   forward the request to [email-masked].  The maintaining authority of
   the extension MUST maintain the accuracy of the record by sending an
   updated full copy of the record to [email-masked] with the subject
   line "LANGUAGE TAG EXTENSION UPDATE" whenever content changes.  Only
   the 'Comments', 'Contact_Email', 'Mailing_List', and 'URL' fields MAY
   be modified in these updates.

   Failure to maintain this record, maintain the corresponding registry,
   or meet other conditions imposed by this section of this document MAY
   be appealed to the IESG [RFC2028] under the same rules as other IETF
   decisions (see [RFC2026]) and MAY result in the authority to maintain
   the extension being withdrawn or reassigned by the IESG.

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   %%
   Identifier:
   Description:
   Comments:
   Added:
   RFC:
   Authority:
   Contact_Email:
   Mailing_List:
   URL:
   %%

   Figure 6: Format of Records in the Language Tag Extensions Registry

   'Identifier' contains the single-character subtag (singleton)
   assigned to the extension.  The Internet-Draft submitted to define
   the extension SHOULD specify which letter or digit to use, although
   the IESG MAY change the assignment when approving the RFC.

   'Description' contains the name and description of the extension.

   'Comments' is an OPTIONAL field and MAY contain a broader description
   of the extension.

   'Added' contains the date the RFC was published in the "full-date"
   format specified in [RFC3339].  For example: 2004-06-28 represents
   June 28, 2004, in the Gregorian calendar.

   'RFC' contains the RFC number assigned to the extension.

   'Authority' contains the name of the maintaining authority for the
   extension.

   'Contact_Email' contains the email address used to contact the
   maintaining authority.

   'Mailing_List' contains the URL or subscription email address of the
   mailing list used by the maintaining authority.

   'URL' contains the URL of the registry for this extension.

   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

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   or meaning inherent in the order of extension subtags.  Extension
   authors SHOULD avoid subtag relationships or canonicalization
   mechanisms that interfere with matching or with length restrictions
   that sometimes exist in common protocols where the extension is used.
   In particular, applications MAY truncate the subtags in doing
   matching or in fitting into limited lengths, so it is RECOMMENDED
   that the most significant information be in the most significant
   (left-most) subtags and that the specification gracefully handle
   truncated subtags.

   When a language tag is to be used in a specific, known, protocol, it
   is RECOMMENDED that that the language tag not contain extensions not
   supported by that protocol.  In addition, note that some protocols
   MAY impose upper limits on the length of the strings used to store or
   transport the language tag.

3.8.  Update of the Language Subtag Registry

   Upon adoption of this document the IANA Language Subtag Registry will
   need an update so that it contains the complete set of subtags valid
   in a language tag.  This collection of subtags, along with a
   description of the process used to create it, is described by
   [registry-update].  IANA will publish the updated version of the
   registry described by this document using the instructions and
   content of [registry-update].  Once published by IANA, the
   maintenance procedures, rules, and registration processes described
   in this document will be available for new registrations or updates.

   Registrations that are in process under the rules defined in
   [RFC4646] when this document is adopted MUST be completed under the
   rules contained in this document.

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4.  Formation and Processing of Language Tags

   This section addresses how to use the information in the registry
   with the tag syntax to choose, form, and process language tags.

4.1.  Choice of Language Tag

   One is sometimes faced with the choice between 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.  It is strongly
   RECOMMENDED that users not define their own rules for language tag
   choice.

   Subtags SHOULD only be used where they add useful distinguishing
   information; extraneous subtags interfere with the meaning,
   understanding, and processing of language tags.  In particular, users
   and implementations SHOULD follow the 'Prefix' and 'Suppress-Script'
   fields in the registry (defined in Section 3.1): these fields provide
   guidance on when specific additional subtags SHOULD (and SHOULD NOT)
   be used in a language tag.

   Of particular note, many applications can benefit from the use of
   script subtags in language tags, as long as the use is consistent for
   a given context.  Script subtags were not formally defined in RFC
   3066 and their use can affect matching and subtag identification by
   implementations of RFC 3066, as these subtags appear between the
   primary language and region subtags.  For example, if a user requests
   content in an implementation of Section 2.5 of [RFC3066] using the
   language range "en-US", content labeled "en-Latn-US" will not match
   the request.  Therefore, it is important to know when script subtags
   will customarily be used and when they ought not be used.  In the
   registry, the Suppress-Script field helps ensure greater
   compatibility between the language tags generated according to the
   rules in this document and language tags and tag processors or
   consumers based on RFC 3066 by defining when users SHOULD NOT include
   a script subtag with a particular primary language subtag.

   Extended language subtags (type 'extlang' in the registry; see
   Section 3.1) also appear between the primary language and region
   subtags.  Applications might benefit from their judicious use in
   forming language tags. [[ guidelines here?? ]]

   Standards, protocols, and applications that reference this document
   normatively but apply different rules to the ones given in this

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   section MUST specify how the procedure varies from the one given
   here.

   The choice of subtags used to form a language tag SHOULD be guided by
   the following rules:

   1.  Use as precise a tag as possible, but no more specific than is
       justified.  Avoid using subtags that are not important for
       distinguishing content in an application.

       *  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.  The script subtag SHOULD NOT be used to form language tags unless
       the script adds some distinguishing information to the tag.  The
       field 'Suppress-Script' in the primary language record in the
       registry indicates script subtags that do not add distinguishing
       information for most applications.

       *  For example, the subtag 'Latn' should not be used with the
          primary language 'en' because nearly all English documents are
          written in the Latin script and it adds no distinguishing
          information.  However, if a document were written in English
          mixing Latin script with another script such as Braille
          ('Brai'), then it might be appropriate to choose to indicate
          both scripts to aid in content selection, such as the
          application of a style sheet.

   3.  Use specific language subtags or subtag sequences in preference
       to subtags for language collections.  A "language collection" is
       a subtag derived from one of the ISO 639-2 codes that represents
       multiple related languages.  For example, the code 'nai'
       represents "North American languages".  The registry contains
       values for the specific languages represented by this collective
       code.  For example 'xxx' (language1) and 'yyy' (language2).  Note
       that the languages contained in a collection (such as the two
       examples shown) are often unrelated except for their inclusion in
       the collection.

   4.  If a tag or subtag has a 'Preferred-Value' field in its registry
       entry, then the value of that field SHOULD be used to form the
       language tag in preference to the tag or subtag in which the
       preferred value appears.

       *  For example, use 'he' for Hebrew in preference to 'iw'.

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   5.  The 'und' (Undetermined) primary language subtag SHOULD NOT be
       used to label content, even if the language is unknown.  Omitting
       the language tag altogether is preferred to using a tag with a
       primary language subtag of 'und'.  The 'und' subtag MAY be useful
       for protocols that require a language tag to be provided.  The
       'und' subtag MAY also be useful when matching language tags in
       certain situations.

   6.  The 'mul' (Multiple) primary language subtag SHOULD NOT be used
       whenever the protocol allows the separate tags for multiple
       languages, as is the case for the Content-Language header in
       HTTP.  The 'mul' subtag conveys little useful information:
       content in multiple languages SHOULD individually tag the
       languages where they appear or otherwise indicate the actual
       language in preference to the 'mul' subtag.

   7.  The same variant subtag SHOULD NOT be used more than once within
       a language tag.

       *  For example, do not use "de-DE-1901-1901".

   To ensure consistent backward compatibility, this document contains
   several provisions to account for potential instability in the
   standards used to define the subtags that make up language tags.
   These provisions mean that no language tag created under the rules in
   this document will become obsolete.

4.2.  Meaning of the Language Tag

   The relationship between the tag and the information it relates to is
   defined by the context in which the tag appears.  Accordingly, this
   section gives only 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 necessary for
      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

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      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 <span lang="fr">C'est la vie.</span> 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 applying the
      inappropriate Norwegian rules.

   Language tags are related when they contain a similar sequence of
   subtags.  For example, if a language tag B contains language tag A as
   a prefix, then B is typically "narrower" or "more specific" than A.
   Thus, "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 might 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 might 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.

4.3.  Length Considerations

   There is no defined upper limit on the size of language tags.  While
   historically most language tags have consisted of language and region
   subtags with a combined total length of up to six characters, larger
   tags have always been both possible and actually appeared in use.

   Neither the language tag syntax nor other requirements in this
   document impose a fixed upper limit on the number of subtags in a
   language tag (and thus an upper bound on the size of a tag).  The
   language tag syntax suggests that, depending on the specific
   language, more subtags (and thus a longer tag) are sometimes
   necessary to completely identify the language for certain
   applications; thus, it is possible to envision long or complex subtag
   sequences.

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4.3.1.  Working with Limited Buffer Sizes

   Some applications and protocols are forced to allocate fixed buffer
   sizes or otherwise limit the length of a language tag.  A conformant
   implementation or specification MAY refuse to support the storage of
   language tags that exceed a specified length.  Any such limitation
   SHOULD be clearly documented, and such documentation SHOULD include
   what happens to longer tags (for example, whether an error value is
   generated or the language tag is truncated).  A protocol that allows
   tags to be truncated at an arbitrary limit, without giving any
   indication of what that limit is, has the potential for causing harm
   by changing the meaning of tags in substantial ways.

   In practice, most language tags do not require more than a few
   subtags and will not approach reasonably sized buffer limitations;
   see Section 4.1.

   Some specifications or protocols have limits on tag length but do not
   have a fixed length limitation.  For example, [RFC2231] has no
   explicit length limitation: the length available for the language tag
   is constrained by the length of other header components (such as the
   charset's name) coupled with the 76-character limit in [RFC2047].
   Thus, the "limit" might be 50 or more characters, but it could
   potentially be quite small.

   The considerations for assigning a buffer limit are:

      Implementations SHOULD NOT truncate language tags unless the
      meaning of the tag is purposefully being changed, or unless the
      tag does not fit into a limited buffer size specified by a
      protocol for storage or transmission.

      Implementations SHOULD warn the user when a tag is truncated since
      truncation changes the semantic meaning of the tag.

      Implementations of protocols or specifications that are space
      constrained but do not have a fixed limit SHOULD use the longest
      possible tag in preference to truncation.

      Protocols or specifications that specify limited buffer sizes for
      language tags MUST allow for language tags of up to 33 characters.

      Protocols or specifications that specify limited buffer sizes for
      language tags SHOULD allow for language tags of at least 42
      characters.

   The following illustration shows how the 42-character recommendation
   was derived.  The combination of language and extended language

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   subtags was chosen for future compatibility.  At up to 15 characters,
   this combination is longer than the longest possible primary language
   subtag (8 characters):

   language      =  3 (ISO 639-2; ISO 639-1 requires 2)
   extlang1      =  4 (each subsequent subtag includes '-')
   extlang2      =  4 (unlikely: needs prefix="language-extlang1")
   extlang3      =  4 (extremely unlikely)
   script        =  5 (if not suppressed: see Section 4.1)
   region        =  4 (UN M.49; ISO 3166 requires 3)
   variant1      =  9 (MUST have language as a prefix)
   variant2      =  9 (MUST have language-variant1 as a prefix)

   total         = 42 characters

   Figure 7: Derivation of the Limit on Tag Length

4.3.2.  Truncation of Language Tags

   Truncation of a language tag alters the meaning of the tag, and thus
   SHOULD be avoided.  However, truncation of language tags is sometimes
   necessary due to limited buffer sizes.  Such truncation MUST NOT
   permit a subtag to be chopped off in the middle or the formation of
   invalid tags (for example, one ending with the "-" character).

   This means that applications or protocols that truncate tags MUST do
   so by progressively removing subtags along with their preceding "-"
   from the right side of the language tag until the tag is short enough
   for the given buffer.  If the resulting tag ends with a single-
   character subtag, that subtag and its preceding "-" MUST also be
   removed.  For example:

   Tag to truncate: zh-Latn-CN-variant1-a-extend1-x-wadegile-private1
   1. zh-Latn-CN-variant1-a-extend1-x-wadegile
   2. zh-Latn-CN-variant1-a-extend1
   3. zh-Latn-CN-variant1
   4. zh-Latn-CN
   5. zh-Latn
   6. zh

   Figure 8: Example of Tag Truncation

4.4.  Canonicalization of Language Tags

   Since a particular language tag is sometimes used by many processes,
   language tags SHOULD always be created or generated in a canonical
   form.

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   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.  Subtags of type 'Region' that have a Preferred-Value mapping in
       the IANA registry (see Section 3.1) SHOULD be replaced with their
       mapped value.  Note: In rare cases, the mapped value will also
       have a Preferred-Value.

   3.  Redundant or grandfathered tags that have a Preferred-Value
       mapping in the IANA registry (see Section 3.1) MUST be replaced
       with their mapped value.  These items either are deprecated
       mappings created before the adoption of this document (such as
       the mapping of "no-nyn" to "nn" or "i-klingon" to "tlh") or are
       the result of later registrations or additions to this document
       (for example, "zh-guoyu" might be mapped to a language-extlang
       combination such as "zh-cmn" by some future update of this
       document).

   4.  Other subtags that have a Preferred-Value mapping in the IANA
       registry (see Section 3.1) MUST be replaced with their mapped
       value.  These items consist entirely of clerical corrections to
       ISO 639-1 in which the deprecated subtags have been maintained
       for compatibility purposes.

   5.  If more than one extension subtag sequence exists, the extension
       sequences are ordered into case-insensitive ASCII order by
       singleton subtag.

   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.

   Example: The language tag "en-BU" (English as used in Burma) is not
   canonical because the 'BU' subtag has a canonical mapping to 'MM'
   (Myanmar), although the tag "en-BU" maintains its validity.

   Canonicalization of language tags does not imply anything about the
   use of upper or lowercase letters when processing or comparing
   subtags (and as described in Section 2.1).  All comparisons MUST be
   performed in a case-insensitive manner.

   When performing canonicalization of language tags, processors MAY
   regularize the case of the subtags (that is, this process is
   OPTIONAL), following the case used in the registry.  Note that this
   corresponds to the following casing rules: uppercase all non-initial
   two-letter subtags; titlecase all non-initial four-letter subtags;

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   lowercase everything else.

   Note: Case folding of ASCII letters in certain locales, unless
   carefully handled, sometimes produces non-ASCII character values.
   The Unicode Character Database file "SpecialCasing.txt" defines the
   specific cases that are known to cause problems with this.  In
   particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is
   uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE).
   Implementers SHOULD specify a locale-neutral casing operation to
   ensure that case folding of subtags does not produce this value,
   which is illegal in language tags.  For example, if one were to
   uppercase the region subtag 'in' using Turkish locale rules, the
   sequence U+0130 U+004E would result instead of the expected 'IN'.

   Note: if the field 'Deprecated' appears in a registry record without
   an accompanying 'Preferred-Value' field, then that tag or subtag is
   deprecated without a replacement.  Validating processors SHOULD NOT
   generate tags that include these values, although the values are
   canonical when they appear in a language tag.

   An extension MUST define any relationships that 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 from "en-b-
   aaa-bbb-ccc").  However, extension specifications SHOULD be designed
   so that they are tolerant of the typical processes described in
   Section 3.7.

4.5.  Considerations for Private Use Subtags

   Private use subtags, like all other subtags, MUST conform to the
   format and content constraints in the ABNF.  Private use subtags have
   no meaning outside the private agreement between the parties that
   intend to use or exchange language tags that employ them.  The same
   subtags MAY be used with a different meaning under a separate private
   agreement.  They SHOULD NOT be used where alternatives exist and
   SHOULD NOT be used 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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   Subtags defined in the IANA registry as having a specific private use
   meaning convey more information that a purely private use tag
   prefixed by the singleton subtag 'x'.  For applications, this
   additional information MAY be useful.

   For example, the region subtags 'AA', 'ZZ', and in the ranges
   'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166 private use codes) MAY
   be used to form a language tag.  A tag such as "zh-Hans-XQ" conveys a
   great deal of public, interchangeable information about the language
   material (that it is Chinese in the simplified Chinese script and is
   suitable for some geographic region 'XQ').  While the precise
   geographic region is not known outside of private agreement, the tag
   conveys far more information than an opaque tag such as "x-someLang",
   which contains no information about the language subtag or script
   subtag outside of the private agreement.

   However, in some cases content tagged with private use subtags MAY
   interact with other systems in a different and possibly unsuitable
   manner compared to tags that use opaque, privately defined subtags,
   so the choice of the best approach sometimes depends on the
   particular domain in question.

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5.  IANA Considerations

   This section deals with the processes and requirements necessary for
   IANA to undertake to maintain the subtag and extension registries as
   defined by this document and in accordance with the requirements of
   [RFC2434].

   The impact on the IANA maintainers of the two registries defined by
   this document will be a small increase in the frequency of new
   entries or updates.

5.1.  Language Subtag Registry

   Upon adoption of this document, IANA will update the registry using
   instructions and content provided in a companion document: [registry-
   update].  The criteria and process for selecting the updated set of
   records are described in that document.  The updated set of records
   represents no impact on IANA, since the work to create it will be
   performed externally.

   Future work on the Language Subtag Registry has been limited to
   inserting or replacing whole records preformatted for IANA by the
   Language Subtag Reviewer as described in Section 3.3 of this document
   and archiving the forwarded registration form.

   Each record MUST be sent to [email-masked] with a subject line
   indicating whether the enclosed record is an insertion of a new
   record (indicated by the word "INSERT" in the subject line) or a
   replacement of an existing record (indicated by the word "MODIFY" in
   the subject line).  Records MUST NOT be deleted from the registry.
   IANA MUST place any inserted or modified records into the appropriate
   section of the language subtag registry, grouping the records by
   their 'Type' field.  Inserted records MAY be placed anywhere in the
   appropriate section; there is no guarantee of the order of the
   records beyond grouping them together by 'Type'.  Modified records
   MUST overwrite the record they replace.

   Included in any request to insert or modify records MUST be a new
   File-Date record.  This record MUST be placed first in the registry.
   In the event that the File-Date record present in the registry has a
   later date than the record being inserted or modified, the existing
   record MUST be preserved.

5.2.  Extensions Registry

   The Language Tag Extensions Registry can contain at most 35 records
   and thus changes to this registry are expected to be very infrequent.

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   Future work by IANA on the Language Tag Extensions Registry is
   limited to two cases.  First, the IESG MAY request that new records
   be inserted into this registry from time to time.  These requests
   MUST include the record to insert in the exact format described in
   Section 3.7.  In addition, there MAY be occasional requests from the
   maintaining authority for a specific extension to update the contact
   information or URLs in the record.  These requests MUST include the
   complete, updated record.  IANA is not responsible for validating the
   information provided, only that it is properly formatted.  It should
   reasonably be seen to come from the maintaining authority named in
   the record present in the registry.

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6.  Security Considerations

   Language tags used in content negotiation, like any other information
   exchanged on the Internet, might be a source of concern because they
   might 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 sent is
   visible to the receiving party and possibly to third parties as well.
   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 (see BCP 72
   [RFC3552] for best current practice guidance on security threats and
   defenses).

   The language tag associated with a particular information item is of
   no consequence whatsoever in determining whether that content might
   contain possible homographs.  The fact that a text is tagged as being
   in one language or using a particular script subtag provides no
   assurance whatsoever that it does not contain characters from scripts
   other than the one(s) associated with or specified by that language
   tag.

   Since there is no limit to the number of variant, private use, and
   extension subtags, and consequently no limit on the possible length
   of a tag, implementations need to guard against buffer overflow
   attacks.  See Section 4.3 for details on language tag truncation,
   which can occur as a consequence of defenses against buffer overflow.

   Although the specification of valid subtags for an extension (see
   Section 3.7) 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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7.  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 the composition of language tags should not have
   any character set issues.

   Rendering of characters based on the content of a language tag is not
   addressed in this memo.  Historically, some languages have relied on
   the use of specific character sets or other information in order to
   infer how a specific character should be rendered (notably this
   applies to language- and culture-specific variations of Han
   ideographs as used in Japanese, Chinese, and Korean).  When language
   tags are applied to spans of text, rendering engines sometimes use
   that information in deciding which font to use in the absence of
   other information, particularly where languages with distinct writing
   traditions use the same characters.

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8.  Changes from RFC 4646

   The main goal for this revision of this document was to incorporate
   ISO 639-3 and its attendent set of language codes into the IANA
   Language Subtag Registry, permitting the identification of many more
   languages and dialects than previously supported.

   The specific changes in this document to meet these goals are:

   o  Defines the incorporation of ISO 639-3 codes as language and
      extlang subtags.  Extlangs are now permitted in language tags.
      The changes necessary to achieve this were:

      *  something

   o  Changed the ABNF related to grandfathered tags.  The irregular
      tags are now listed.  Users of RFC 4646 sometimes made the mistake
      of implementing the grandfathered ABNF without checking the actual
      list of tags, thus allowing some illegal tags.  Also: added
      description of both types of grandfathered tags to Section 2.2.8.

   o  Added the paragraph on "collections" to Section 4.1.

   o  Changed the capitalization rules for 'Tag' fields in Section 3.1.

   o  Split section 3.1 up into subsections.

   o  Modified section 3.5 to allow Suppress-Script fields to be added,
      modified, or removed via the registration process.  This was an
      erratum from RFC 4646.

   o  Modified examples that used region code 'CS' (formerly Serbia and
      Montenegro) to use 'RS' (Serbia) instead.

   o  Modified the rules for creating and maintaining record
      'Description' fields to prevent duplicates, including inverted
      duplicates.

   o  Removed the lengthy description of why RFC 4646 was created from
      this section, which also caused the removal of the reference to
      XML Schema.

   o  Modified the ABNF to eliminate the redundant use of upper and
      lowercase letters in the products (for example, the sequence
      ("x"/"X") in the private-use production is now ("x")).  The text
      in section 2.1 was also edited and rearranged to place more
      emphasis on this fact.

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   o  Replaced the example "fr-Latn-CA" in Section 2.1 with "sr-Latn-RS"
      and "az-Arab-IR" because "fr-Latn-CA" doesn't respect the
      Suppress-Script on 'Latn' with 'fr'.

   o  Changed the requirements for well-formedness to make singleton
      repetition checking optional (it is required for validity
      checking) in Section 2.2.9.

   o  Changed the note about irregular grandfathered tags in the ABNF to
      say 'grandfathered tags that don't match langtag'.

   o  Changed the text in Section 2.2.9 refering to grandfathered
      checking to note that the list is now included in the ABNF.

   o  Added text to Section 3.2 making clear that the Language Subtag
      Reviewer may delegate various non-critical duties, including list
      moderation.

   o  Added text to Section 3.5 clarifying that the ietf-languages list
      is operated by whomever the IESG appoints.

   o  Added text to Section 3.1.4 clarifying that the first Description
      in a 'language' or 'extlang' record matches the corresponding
      Reference Name for the language in ISO 639-3.

   o  Added text to the end of Section 3.1.2 noting that future versions
      of this document might add new field types and recommending that
      implementations ignore any unrecognized fields.

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9.  References

9.1.  Normative References

   [ISO10646]
              International Organization for Standardization, "ISO/IEC
              10646:2003. Information technology -- Universal Multiple-
              Octet Coded Character Set (UCS)", 2003.

   [ISO15924]
              International Organization for Standardization, "ISO
              15924:2004. Information and documentation -- Codes for the
              representation of names of scripts", January 2004.

   [ISO3166-1]
              International Organization for Standardization, "ISO 3166-
              1:1997. Codes for the representation of names of countries
              and their subdivisions -- Part 1: Country codes", 1997.

   [ISO639-1]
              International Organization for Standardization, "ISO 639-
              1:2002. Codes for the representation of names of languages
              -- Part 1: Alpha-2 code", 2002.

   [ISO639-2]
              International Organization for Standardization, "ISO 639-
              2:1998. Codes for the representation of names of languages
              -- Part 2: Alpha-3 code, first edition", 1998.

   [ISO646]   International Organization for Standardization, "ISO/IEC
              646:1991, Information technology -- ISO 7-bit coded
              character set for information interchange.", 1991.

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2028]  Hovey, R. and S. Bradner, "The Organizations Involved in
              the IETF Standards Process", BCP 11, RFC 2028,
              October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC2860]  Carpenter, B., Baker, F., and M. Roberts, "Memorandum of

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              Understanding Concerning the Technical Work of the
              Internet Assigned Numbers Authority", RFC 2860, June 2000.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, July 2002.

   [RFC4234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.

   [RFC4645]  Ewell, D., Ed., "Initial Language Subtag Registry",
              September 2006, <http://www.ietf.org/rfc/rfc4645.txt>.

   [RFC4647]  Phillips, A., Ed. and M. Davis, Ed., "Matching of Language
              Tags", September 2006,
              <http://www.ietf.org/rfc/rfc4647.txt>.

   [UN_M.49]  Statistics 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.

9.2.  Informative References

   [RFC1766]  Alvestrand, H., "Tags for the Identification of
              Languages", RFC 1766, March 1995.

   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)
              Part Three: Message Header Extensions for Non-ASCII Text",
              RFC 2047, November 1996.

   [RFC2231]  Freed, N. and K. Moore, "MIME Parameter Value and Encoded
              Word Extensions: Character Sets, Languages, and
              Continuations", RFC 2231, November 1997.

   [RFC2781]  Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO
              10646", RFC 2781, February 2000.

   [RFC3066]  Alvestrand, H., "Tags for the Identification of
              Languages", BCP 47, RFC 3066, January 2001.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [RFC4646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for the
              Identification of Languages", September 2006,
              <http://www.ietf.org/rfc/rfc4646.txt>.

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   [Unicode]  Unicode Consortium, "The Unicode Consortium. The Unicode
              Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003.
              ISBN 0-321-49081-0)", January 2007.

   [XML10]    Bray (et al), T., "Extensible Markup Language (XML) 1.0",
              02 2004.

   [iso639.prin]
              ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory
              Committee:  Working principles for ISO 639 maintenance",
              March 2000,
              <http://www.loc.gov/standards/iso639-2/
              iso639jac_n3r.html>.

   [record-jar]
              Raymond, E., "The Art of Unix Programming", 2003,
              <urn:isbn:0-13-142901-9>.

   [registry-update]
              Ewell, D., Ed., "Update to the Language Subtag Registry",
              September 2006, <http://www.ietf.org/internet-drafts/
              draft-ietf-ltru-initial-registry-00.txt>.

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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 4646, RFC 4647, 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 contributed to this document:

   Stephane Bortzmeyer, Karen Broome, Peter Constable, John Cowan,
   Martin Duerst, Frank Ellerman, Doug Ewell, Marion Gunn, Randy
   Presuhn, 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 go to Michael Everson, who served as the Language Tag
   Reviewer for almost the entire RFC 1766/RFC 3066 period, as well as
   the Language Subtag Reviewer since the adoption of RFC 4646.

   Special thanks also to Doug Ewell ("the Official Doug"), for his
   production of the first complete subtag registry, his work to support
   and maintain new registrations, and his careful editorship of both
   RFC 4645 and [registry-update].

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Appendix B.  Examples of Language Tags (Informative)

   Simple language subtag:

      de (German)

      fr (French)

      ja (Japanese)

      i-enochian (example of a grandfathered tag)

   Language subtag plus Script subtag:

      zh-Hant (Chinese written using the Traditional Chinese script)

      zh-Hans (Chinese written using the Simplified Chinese script)

      sr-Cyrl (Serbian written using the Cyrillic script)

      sr-Latn (Serbian written using the Latin script)

   Language-Script-Region:

      zh-Hans-CN (Chinese written using the Simplified script as used in
      mainland China)

      sr-Latn-RS (Serbian written using the Latin script as used in
      Serbia)

   Language-Variant:

      sl-rozaj (Resian dialect of Slovenian

      sl-nedis (Nadiza dialect of Slovenian)

   Language-Region-Variant:

      de-CH-1901 (German as used in Switzerland using the 1901 variant
      [orthography])

      sl-IT-nedis (Slovenian as used in Italy, Nadiza dialect)

   Language-Script-Region-Variant:

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      sl-Latn-IT-nedis (Nadiza dialect of Slovenian written using the
      Latin script as used in Italy.  Note that this tag is NOT
      RECOMMENDED because subtag 'sl' has a Suppress-Script value of
      'Latn')

   Language-Region:

      de-DE (German for Germany)

      en-US (English as used in the United States)

      es-419 (Spanish appropriate for the Latin America and Caribbean
      region using the UN region code)

   Private use subtags:

      de-CH-x-phonebk

      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 registry values:

      x-whatever (private use using the singleton 'x')

      qaa-Qaaa-QM-x-southern (all private tags)

      de-Qaaa (German, with a private script)

      sr-Latn-QM (Serbian, Latin-script, private region)

      sr-Qaaa-RS (Serbian, private script, for Serbia)

   Tags that use extensions (examples ONLY: extensions MUST be defined
   by revision or update to this document or by RFC):

      en-US-u-islamCal

      zh-CN-a-myExt-x-private

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      en-a-myExt-b-another

   Some Invalid Tags:

      de-419-DE (two region tags)

      a-DE (use of a single-character subtag in primary position; note
      that there are a few grandfathered tags that start with "i-" that
      are valid)

      ar-a-aaa-b-bbb-a-ccc (two extensions with same single-letter
      prefix)

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Authors' Addresses

   Addison Phillips (editor)
   Yahoo! Inc.

   Email: [email-masked]
   URI:   http://www.inter-locale.com

   Mark Davis (editor)
   Google

   Email: [email-masked] or [email-masked]

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Acknowledgment

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https://www1.ietf.org/mailman/listinfo/ltru

---

From: Stephane Bortzmeyer <[email-masked]>
Date: Thu, 28 Dec 2006 11:49:27 +0100

On Mon, Dec 18, 2006 at 04:34:03PM -0800,
 Addison Phillips <[email-masked]> wrote 
 a message of 2657 lines which said:

>    Extended language subtags (examples ONLY: extended languages MUST
>    be defined by revision or update to this document):

Isn't the restriction obsolete for 4646bis?

---

From: Addison Phillips <[email-masked]>
Date: Thu, 28 Dec 2006 10:27:04 -0800

Good catch.