Network Working Group                                   A. Phillips, Ed.
Internet-Draft                                            Quest Software
Expires: December 4, 5, 2005                                  M. Davis, Ed.
                                                                     IBM
                                                           June 02, 03, 2005

                     Tags for Identifying Languages
                      draft-ietf-ltru-registry-03
                      draft-ietf-ltru-registry-04

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Copyright Notice

   Copyright (C) The Internet Society (2005).

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.  This
   document obsoletes RFC 3066 (which replaced RFC 1766).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The Language Tag . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1   Syntax . . . . . . . . . . . . . . . . . . . . . . . . . .  4
       2.1.1   Length Considerations  . . . . . . . . . . . . . . . .  6
     2.2   Language Subtag Sources and Interpretation . . . . . . . .  7  8
       2.2.1   Primary Language Subtag  . . . . . . . . . . . . . . .  9
       2.2.2   Extended Language Subtags  . . . . . . . . . . . . . . 11
       2.2.3   Script Subtag  . . . . . . . . . . . . . . . . . . . . 11 12
       2.2.4   Region Subtag  . . . . . . . . . . . . . . . . . . . . 12 13
       2.2.5   Variant Subtags  . . . . . . . . . . . . . . . . . . . 13 14
       2.2.6   Extension Subtags  . . . . . . . . . . . . . . . . . . 14 15
       2.2.7   Private Use Subtags  . . . . . . . . . . . . . . . . . 15 16
       2.2.8   Pre-Existing RFC 3066 Registrations  . . . . . . . . . 16 17
       2.2.9   Classes of Conformance . . . . . . . . . . . . . . . . 16 17
   3.  Registry Format and Maintenance  . . . . . . . . . . . . . . . 18 19
     3.1   Format of the IANA Language Subtag Registry  . . . . . . . 18 19
     3.2   Maintenance of the Registry  . . . . . . . . . . . . . . . 23 24
     3.3   Stability of IANA Registry Entries . . . . . . . . . . . . 24 25
     3.4   Registration Procedure for Subtags . . . . . . . . . . . . 27 28
     3.5   Possibilities for Registration . . . . . . . . . . . . . . 30 31
     3.6   Extensions and Extensions Namespace  . . . . . . . . . . . 32 33
     3.7   Initialization of the Registry . . . . . . . . . . . . . . 35 36
   4.  Formation and Processing of Language Tags  . . . . . . . . . . 38 39
     4.1   Choice of Language Tag . . . . . . . . . . . . . . . . . . 38 39
     4.2   Meaning of the Language Tag  . . . . . . . . . . . . . . . 40 41
     4.3   Canonicalization of Language Tags  . . . . . . . . . . . . 41 42
     4.4   Considerations for Private Use Subtags . . . . . . . . . . 43 44
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 44 45
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 45 46
   7.  Character Set Considerations . . . . . . . . . . . . . . . . . 46 47
   8.  Changes from RFC 3066  . . . . . . . . . . . . . . . . . . . . 47 48
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 51 52
     9.1   Normative References . . . . . . . . . . . . . . . . . . . 51 52
     9.2   Informative References . . . . . . . . . . . . . . . . . . 52 53
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 53 54
   A.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 54 55
   B.  Examples of Language Tags (Informative)  . . . . . . . . . . . 55 56
   C.  Example Registry . . . . . . . . . . . . . . . . . . . . . . . 58 59
       Intellectual Property and Copyright Statements . . . . . . . . 62 63

1.  Introduction

   Human beings on our planet have, past and present, used a number of
   languages.  There are many reasons why one would want to identify the
   language used when presenting or requesting information.

   Information about a user's language preferences commonly needs to be
   identified so that appropriate processing can be applied.  For
   example, the user's language preferences in a browser can be used to
   select web pages appropriately.  A choice of language preference can
   also be used to select among tools (such as dictionaries) to assist
   in the processing or understanding of content in different languages.

   In addition, knowledge about the particular language used by some
   piece of information content may might be useful or even required by some
   types of information processing; for example spell-checking,
   computer-synthesized speech, Braille transcription, or high-quality
   print renderings.

   One means of indicating the language used is by labeling the
   information content with a language identifier.  These identifiers
   can also be used to specify user preferences when selecting
   information content, or for labeling additional attributes of content
   and associated resources.

   These identifiers can also be used to indicate additional attributes
   of content that are closely related to the language.  In particular,
   it is often necessary to indicate specific information about the
   dialect, writing system, or orthography used in a document or
   resource, as these attributes may be important for the user to obtain
   information in a form that they can understand, or important in
   selecting appropriate processing resources for the given content.

   This document specifies an identifier mechanism and a registration
   function for values to be used with that identifier mechanism.  It
   also defines a mechanism for private use values and future extension.

   This document replaces RFC 3066, which replaced RFC 1766.  For a list
   of changes in this document, see Section 8.

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [10].

2.  The Language Tag

2.1  Syntax

   The language tag is composed of one or more parts: A primary language
   subtag and a (possibly empty) series of subsequent subtags.  Subtags
   are distinguished by their length, position in the subtag sequence,
   and content, so that each type of subtag can be recognized solely by
   these features.  This makes it possible to construct a parser that
   can extract and assign some semantic information to the subtags, even
   if specific subtag values are not recognized.  Thus a parser need not
   have an up-to-date copy of the registered subtag values to perform
   most searching and matching operations.

   The syntax of this tag in ABNF [7] is:

   Language-Tag = (lang
                   *3("-" extlang)
                   ["-" script]
                   ["-" region]
                   *("-" variant)
                   *("-" extension)
                   ["-" privateuse])
                   / privateuse         ; private-use tag
                   / grandfathered      ; grandfathered registrations

   lang            = 2*4ALPHA           ; shortest ISO 639 code
                   / registered-lang
   extlang         = 3ALPHA             ; reserved for future use
   script          = 4ALPHA             ; ISO 15924 code
   region          = 2ALPHA             ; ISO 3166 code
                   / 3DIGIT             ; UN country number
   variant         =  5*8alphanum       ; registered variants
                   / ( DIGIT 3alphanum )
   extension       = singleton 1*("-" (2*8alphanum))
   privateuse      = ("x"/"X") 1*("-" (1*8alphanum))
   singleton       = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT
                   ; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9"
                   ; Single letters: x/X is reserved for private use
   registered-lang = 4*8ALPHA          ; registered language subtag
   grandfathered   = 1*3ALPHA 1*2("-" (2*8alphanum))
                                       ; grandfathered registration
                                       ; Note: i is the only singleton
                                       ; that starts a grandfathered tag
   alphanum        = (ALPHA / DIGIT)   ; letters and numbers

                        Figure 1: Language Tag ABNF

   The character "-" is HYPHEN-MINUS (ABNF: %x2D).  All subtags have a
   maximum length of eight characters.  Note that there is a subtlety in
   the ABNF for 'variant': variants starting with a digit may MAY be only four
   characters long, while those starting with a letter must MUST be at least
   five characters long.

   Whitespace is not permitted in a language tag.  For examples of
   language tags, see Appendix B.

   Note that although [7] refers to octets, the language tags described
   in this document are sequences of characters from the US-ASCII
   repertoire.  Language tags may 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 [12] encoding of Unicode [20]. [21].

   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 should MUST not be taken to
   carry meaning.

   For example:

   o  [ISO 639] [1] recommends that language codes be written in lower
      case ('mn' Mongolian).

   o  [ISO 3166] [4] recommends that country codes be capitalized ('MN'
      Mongolia).

   o  [ISO 15924] [3] recommends that script codes use lower case 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.

2.1.1  Length Considerations

   Although neither

   RFC 3066 [24] did not provide an upper limit on the ABNF nor other guidelines size of language
   tags.  While RFC 3066 did define the semantics of particular subtags
   in such a way that most language tags consisted of language and
   region subtags with a combined total length of up to six characters,
   much larger registered tags were not only possible but were actually
   registered.

   Neither this document
   provide nor the syntax in the ANBF imposes a fixed
   upper limit on the number of subtags in a Language
   Tag language tag (and thus the an
   upper bound on the size of a tag) and tag).  The syntax in this document
   suggests that, depending on the specific language, more subtags (and
   thus characters) are sometimes necessary to form a complete tag; thus
   it is possible to envision quite long and or complex subtag sequences, in
   practice these are rare because additional granularity in tags seldom
   adds useful distinguishing information sequences.

   Some applications and because longer, more
   granular tags interefere with protocols are forced to allocate fixed buffer
   sizes or otherwise limit the meaning, understanding, and
   processing length of a language tags. tag in a particular
   application.  A conformant implementation or specification MAY refuse
   to support the storage of language tags which exceed a specified
   length.  For an example, see
   [RFC 2231] [22].  Any such limitation SHOULD be clearly documented, and such
   documentation SHOULD include the disposition of any longer tags (for
   example, whether an error value is generated or the language tag is
   truncated).  If truncation is permitted it MUST NOT
   permit a subtag to be divided.  Implementations that restrict storage
   should consider removing extensions before processing.  A protocol
   that allows

   In practice, most tags to do not require additional subtags or
   substantially more characters.  Additional subtags sometimes add
   useful distinguishing information, but extraneous subtags interfere
   with the meaning, understanding, and processing of language tags.
   Since language tags MAY be truncated at by an arbitrary limit, application or protocol
   that limits tag sizes, when choosing language tags users and
   applications SHOULD avoid adding subtags that add no distinguishing
   value.  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.
   (For more information on selecting subtags, see Section 4.1.)

   Implementations MUST support a limit of at least 33 characters.  This
   limit includes at least one subtag of each non-extension, non-private
   use type.  When choosing a buffer limit, a length of at least 42
   characters is strongly RECOMMENDED.

   If truncation is permitted it MUST NOT permit a subtag to be divided
   or the formation of invalid tags (for example, one ending with the
   "-" character).  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 particular,  variant subtags SHOULD be used only with their
   recommended prefix.  In practice, this limits most tags to a sequence
   of four subtags, and thus

   Some specifications are space constrained but do not have a maximum fixed
   length of 26 characters
   (excluding any extensions or private use sequences). limitation.  For example, see [RFC 2231] [23].  This protocol
   has no explicit length limitation: the language tag's length is because
   subtags are
   limited to a by the length of eight characters and other header components (such as the extlang,
   script, and region subtags are limited to even fewer characters.  See
   Section 4.1 for
   charset's name) coupled with the 78 character limit in [RFC 2822]
   [14].  Thus the "limit" might be 60 or more information on selecting characters, but it could
   potentially be quite small.  In these cases, implementations SHOULD
   use the most appropriate
   Language Tag.

   Longer tags are possible.  The longest tags (excluding extensions)
   could have a length possible language tag.  Warning the user of up to 62 characters,
   truncation, if necessary, is RECOMMENDED, as shown below.
   Implementations MUST be able to handle tags truncation can change
   the semantic meaning of this length without
   truncation.  Support for tags the tag.

   The following illustration shows how the 42-character recommendation
   was derived.  The combination of language and extended language
   subtags was chosen for future compatibility.  At up to 64 characters 11 characters,
   this combination is RECOMMENDED.
   Implementations MAY support longer tags.

   Here is how the 62-character length of than the longest practical tag
   (excluding extensions) is derived: longest possible 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) M.49; ISO 3166 requires 3)
   variant1      =  9 (MUST have language as a prefix)
   variant2      =  9 (unlikely: needs prefix="language-variant1")
   private use 1 = 11 ("-x-" + subtag)
   private use 2 = 9 (MUST have language-variant1 as a prefix)

   total         = 62 42 characters

              Figure 2: Derviation Derivation of the Limit on Tag Length

   Applications or protocols which have to truncate a tag MUST do so by
   progressively removing subtags along with their preceding "-" from
   the right side of the Longest 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-Hant-CN-variant1-a-extend1-x-wadegile-private1
   1. zh-Hant-CN-variant1-a-extend1-x-wadegile
   2. zh-Hant-CN-variant1-a-extend1
   3. zh-Hant-CN-variant1
   4. zh-Hant-CN
   5. zh-Hant
   6. zh

                    Figure 3: Example of Tag Truncation

2.2  Language Subtag Sources and Interpretation

   The namespace of language tags and their subtags is administered by
   the Internet Assigned Numbers Authority (IANA) [13] according to the
   rules in Section 5 of this document.  The registry maintained by IANA
   is the source for valid subtags: other standards referenced in this
   section provide the source material for that registry.

   Terminology in this section:

   o  Tag or tags refers to a complete language tag, such as
      "fr-Latn-CA".  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 'Latn' in "fr-Latn-CA".  Examples of subtags in
      this document are enclosed in single quotes ('Latn').

   o  Code or codes refers to values defined in external standards (and
      which are used as subtags in this document).  For example, 'Latn'
      is an [ISO 15924] [3] script code which was used to define the
      'Latn' script subtag for use in a language tag.  Examples of codes
      in this document are enclosed in single quotes ('en', 'Latn').

   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 digit subtags are reserved for current or future
   use.  These include the following current uses:

   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 3.6.

   The single letter subtag 'i' is used by some grandfathered tags, such
   as "i-enochian", 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 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" [ISO 639-1] [1], or
       using assignments subsequently made by the ISO 639 Part 1
       maintenance agency or governing standardization bodies.

   2.  All three character language subtags were defined in the IANA
       registry according to the assignments found in ISO 639 Part 2,
       "ISO 639-2:1998 - Codes for the representation of names of
       languages -- Part 2: Alpha-3 code - edition 1" [ISO 639-2] [2],
       or assignments subsequently made by the ISO 639 Part 2
       maintenance agency 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 4.4
       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 3.4
       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 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 4.4.

   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 an ISO 639-2 three character code, 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 not expected that future
   assignments of this nature will 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 [16]: [17]:

   "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."

   In order to avoid instability of 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 ISO 639-2, the two character
   code will not be added as a subtag in the registry.  See Section 3.3.

   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.

   For example, 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

   The following rules apply to the extended language subtags:

   1.  Three letter subtags immediately following the primary subtag are
       reserved for future standardization, anticipating work that is
       currently under way on ISO 639.

   2.  Extended language subtags MUST follow the primary subtag and
       precede any other subtags.

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

   4.  Extended language subtags will not be registered except by
       revision of this document.

   5.  Extended language subtags MUST NOT be used to form language tags
       except by revision of this document.

   Extended language subtag records, once they appear in the registry,
   MUST include exactly one 'Prefix' field indicating an appropriate
   language subtag or sequence of subtags that MUST always appear as a
   prefix to the extended language subtag.

   Example: In a future revision or update of this document, the tag
   "zh-gan" (registered under RFC 3066) might become a valid non-
   grandfathered (that is, redundant) tag in which the subtag 'gan'
   might represent the Chinese dialect 'Gan'.

2.2.3  Script Subtag

   The following rules apply to the script subtags:

   1.  All four character subtags were defined according to ISO 15924
       [3]--"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 4.4 for more
       information on private-use subtags.

   4.  Script subtags cannot be registered using the process in
       Section 3.4 of this document.  Variant subtags may MAY be considered
       for registration for that purpose.

   Example: "de-Latn" represents German written using the Latin script.

2.2.4  Region Subtag

   The following rules apply to the region subtags:

   1.  The region subtag defines language variations used in a specific
       region, geographic, or political area.  Region subtags MUST
       follow any language, extended language, or script subtags and
       MUST precede all other subtags.

   2.  All two character subtags following the primary subtag were
       defined in the IANA registry according to the assignments found
       in ISO 3166 [4]--"Codes for the representation of names of
       countries and their subdivisions - Part 1: Country
       codes"--alpha-2 country codes or assignments subsequently made by
       the ISO 3166 maintenance agency or governing standardization
       bodies.

   3.  All three character codes consisting of digit (numeric)
       characters were defined in the IANA registry according to the
       assignments found in UN Standard Country or Area Codes for
       Statistical  Use [5] 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:

       A.  UN numeric codes assigned to 'macro-geographical
           (continental)' or sub-regions not associated with an assigned
           ISO 3166 alpha-2 code _are_ defined.

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

       C.  UN numeric codes for countries with ambiguous ISO 3166
           alpha-2 codes as defined in Section 3.3 are defined in the
           registry and are canonical for the given country or region
           defined.

       D.  The alphanumeric codes in Appendix X of the UN document are
           _not_ defined and MUST NOT be used to form language tags.
           (At the time this document was created these values match the
           ISO 3166 alpha-2 codes.)
   4.  There may MUST be at most one region subtag in a language tag.

   5.  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 4.4 for more information on private use subtags.

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

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

   "es-419" represents Spanish ('es') as used in the UN-defined Latin
   America and Caribbean region ('419').

2.2.5  Variant 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 3.4.

   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 3.4 of this document before being used to form
       language tags.  In order to distinguish variants from other types
       of subtags, registrations must 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 MAY include
   one or more 'Prefix' fields, which indicates 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 'scouse' has a Prefix of "en", making it suitable
   to form language tags such as "en-scouse" and "en-GB-scouse", but not
   suitable for use in a tag such as "zh-scouse" or "it-GB-scouse".

   "en-scouse" represents the Scouse dialect of English.

   "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 variantions '1996' and '1901' should
   not SHOULD
   NOT be used in the same tag, as they represent the dates of different
   spelling reforms.  A variant that may can meaningfully be used in
   combination with another variant should 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

   The following rules apply to extensions:

   1.   Extension subtags are separated from the other subtags defined
        in this document by a single-letter subtag ("singleton").  The
        singleton MUST be one allocated to a registration authority via
        the mechanism described in Section 3.6 and cannot 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 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'.

   11.  In the event that more than one extension appears in a single
        tag, the tag SHOULD be canonicalized as described in
        Section 4.3.

   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

   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 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.

   3.  A tag MAY consist entirely of private-use subtags.

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

   For example: Users who wished to utilize SIL Ethnologue for
   identification might agree to exchange tags such as "az-Arab-x-AZE-
   derbend".  This example contains two private-use subtags.  The first
   is 'AZE' and the second is 'derbend'.

2.2.8  Pre-Existing RFC 3066 Registrations

   Existing IANA-registered language tags from RFC 1766 and/or RFC 3066
   maintain their validity.  IANA will maintain these tags in the
   registry under either the "grandfathered" or "redundant" type.  For
   more information see Section 3.7.

   It is important to note that all language tags formed under the
   guidelines in this document were either legal, well-formed tags or
   could have been registered under RFC 3066.

2.2.9  Classes of Conformance

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

   An implementation that claims to check for well-formed language tags
   MUST:

   o  Check that the tag and all of its subtags, including extension and
      private-use subtags, conform to the ABNF or that the tag is on the
      list of grandfathered tags.

   o  Check that singleton subtags that identify extensions do not
      repeat.  For example, the tag "en-a-xx-b-yy-a-zz" is not well-
      formed.

   Well-formed processors are strongly encouraged to implement the
   canonicalization rules contained in Section 4.3.

   An implementation that claims to be validating MUST:

   o  Check that the tag is well-formed.

   o  Specify the particular registry date for which the implementation
      performs validation of subtags.

   o  Check that either the tag is a grandfathered tag, or that all
      language, script, region, and variant subtags consist of valid
      codes for use in language tags according to the IANA registry as
      of the particular date specified by the implementation.

   o  Specify which, if any, extension RFCs as defined in Section 3.6
      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 variant and extended language subtags, if the registry
      contains one or more 'Prefix' fields for that subtag, check that
      the tag matches at least one prefix.  The tag matches if all the
      subtags in the 'Prefix' also appear in the tag.  For example, the
      prefix "es-CO" matches the tag "es-Latn-CO-x-private" because both
      the 'es' language subtag and 'CO' region subtag appear in the tag.

3.  Registry Format and Maintenance

   This section defines the Language Subtag Registry and the maintenance
   and update procedures associated with it.

   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.)

   The registry defined under this document 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.

3.1  Format of the IANA Language Subtag Registry

   The IANA Language Subtag Registry ("the registry") will consist of a
   text file that is machine readable in the format described in this
   section, plus copies of the registration forms approved by the
   Language Subtag Reviewer in accordance with the process described in
   Section 3.4.  With the exception of the registration forms for
   grandfathered and redundant tags, no registration records will be
   maintained for the initial set of subtags.

   The registry will be in a modified record-jar format text file [17]. [18].
   Lines are 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 [7]):

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

   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 alphabetically within that range, including the values explicitly
   mentioned.  For example 'a..c' denotes the values 'a', 'b', and 'c'.

   Characters from outside the US-ASCII 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 XML 1.0 [18] [19] (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 ISO/IEC 10646 [6] 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 MAY have between two and six digits.

   All fields whose field-body contains a date value use the "full-date"
   format specified in RFC 3339 [14]. [15].  For example: "2004-06-28"
   represents June 28, 2004 in the Gregorian calendar.

   The first record in the file contains the single field whose field-
   name is "File-Date".  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
   %%

   Subsequent records represent subtags in the registry.  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-value 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-value 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-value contains a complete language tag.  This field
         MUST only appear in records whose Type has one of these values:
         "grandfathered" or "redundant".

   o  Description

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

   o  Added

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

   The 'Subtag' or 'Tag' field MUST use lowercase letters to form the
   subtag or tag, 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.

   The field 'Description' MAY appear more than one time.  At least one
   of the  'Description' fields must MUST contain a description of the tag
   being registered written or transcribed into the Latin script; the
   same or additional fields may MAY also include a description in a non-
   Latin script.  The 'Description' field is used for identification
   purposes and should not SHOULD NOT be taken to represent the actual native name
   of the language or variation or to be in any particular language.
   Most descriptions are taken directly from source standards such as
   ISO 639 or ISO 3166.

   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.

   Each record MAY also contain the following fields:

   o  Preferred-Value

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

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

   o  Deprecated

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

   o  Prefix

      *  Prefix's field-value contains a language tag with which this
         subtag may 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-value is 'variant' or 'extlang'.  For
         example, the 'Prefix' for the variant 'scouse' is 'en', meaning
         that the tags "en-scouse" and "en-GB-scouse" might be
         appropriate while the tag "is-scouse" 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-value is 'language'.  See Section 4.1.

   The field 'Deprecated' MAY be added to any record via the maintenance
   process described in Section 3.2 or via the registration process
   described in Section 3.4.  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 may 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.

   Thie field 'Preferred-Value' contains a mapping between the record in
   which it appears and a tag or subtag which should SHOULD be preferred when
   selected language tags.  These values form three groups:

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

      ISO 3166 region codes which 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 warrents a new region code.

      Tags grandfathered 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 MAY be beneficial to
   applications that are matching, selecting, for filtering content
   based on its language tags.

   It should be noted

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

   In particular, the 'Preferred-Value' field does not imply that retagging
   content formerly tagged with one tag should be retagged. 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 of type "grandfathered"
   and "region" according to the rules in Section 3.2.  Otherwise the
   field MUST NOT be added to any record already in the registry.

   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'.

   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.

   The field-value of the 'Prefix' field consists of a language tag
   whose subtags are appropriate to use with this subtag.  For example,
   the variant subtag 'scouse' has a recommended prefix Prefix field of "en".  This means
   that tags starting with the prefix sequence "en-" are most appropriate with
   this subtag, so "en-Latn-scouse" and "en-GB-scouse" are both
   acceptable, while the tag "fr-scouse" is an inappropriate choice.

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

   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.  Long screeds about a particular subtag are frowned
   upon.

   The field 'Suppress-Script' MUST only appear in records whose 'Type'
   field-value is 'language'.  This field may MAY appear at most one time in
   a record.  This field indicates a script used to write the
   overwhelming majority of documents for the given language and which
   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".

   For examples of registry entries and their format, see Appendix C.

3.2  Maintenance of the Registry

   Maintenance of the registry requires that as codes are assigned or
   withdrawn by ISO 639, ISO 15924, and ISO 3166, the Language Subtag
   Reviewer will evaluate each change, determine whether it conflicts
   with existing registry entries, and submit the information to IANA
   for inclusion in the registry.  If an change takes place and the
   Language Subtag Reviewer does not do this in a timely manner, then
   any interested party may MAY use the procedure in Section 3.4 to register
   the appropriate update.

   Note: The redundant and grandfathered entries together are the
   complete list of tags registered under RFC 3066 [23]. [24].  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 are those that can never be legal under those
   same provisions.

   The set of redundant and grandfathered tags is permanent and stable:
   no new entries will be added and none of the entries will be removed.
   Records of type 'grandfathered' may MAY have their type converted to
   'redundant': see  Section 3.7 for more information.

   RFC 3066 tags that were deprecated prior to the adoption of this
   document 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.  If a change or addition to the
   registry is required, needed, the Language Subtag Reviewer will prepare the
   complete record, including all fields, and forward it to IANA for
   insertion into the registry.  If this represents a new subtag, then
   the message will indicate that this represents an INSERTION of a
   record.  If this represents a change to an existing subtag, then the
   message must MUST indicate that this represents a MODIFICATION, as shown
   in the following example:

   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 5 6

   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 RFC 3339 [14] [15] "full-date"
   format.

   Values in the 'Subtag' field must MUST be lowercase except as provided for
   in Section 3.1.

3.3  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:

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

   o  Values in the 'Description' field MUST NOT be changed in a way
      that would invalidate previously-existing tags.  They may 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: an historical example of
      this would be "Upper Volta" changing to "Burkina Faso".

   o  Values in the field 'Prefix' MAY be added to records of type
      'variant' via the registration process.

   o  Values in the field 'Prefix' MAY be modified, so long as the
      modifications broaden the set of recommended prefixes.  That is, a
      recommended 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 ranges "en-Latn", prefixes "en-
      Latn", "fr", or "en-US-boont".  If one of those prefixes were
      needed, a new Prefix SHOULD be registered.

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

   o  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.

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

   o  Codes assigned by ISO 639, 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 and their value is
      canonical for the meaning assigned to them.

   o  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 withdrawl is 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 MAY also be added.  The
      registration process MAY be used to add comments about the
      withdrawal of the code by the respective standard.

      *  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').

   o  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:

      *  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 3.4, shall 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 MUST conform
         to other restrictions on language subtags in this document.

      *  For all subtags whose meaning is derived from an external
         standard (i.e.  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 MA/RA has adopted a similar stability
         policy.

      *  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 3.4, shall 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 MUST conform to
         other restrictions on variant subtags in this document.

      *  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
         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.

      *  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 then the Language Subtag Reviewer,
         as described in Section 3.4, shall SHALL prepare a proposal for
         entering the appropriate numeric UN country code as an entry in
         the IANA registry.

      *  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
         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 MUST conform to other restrictions on variant
         subtags in this document.  This situation is very unlikely to
         ever occur.

   o  Stability provisions apply to grandfathered tags with this
      exception: should all of the subtags in a grandfathered tag become
      valid subtags in the IANA registry, then the 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, if the subtag 'gan' in the language tag
      "zh-gan" were to be registered as an extended language subtag,
      then the grandfathered tag "zh-gan" would be deprecated (but
      existing content or implementations that use "zh-gan" would remain
      valid).

3.4  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
   required needed
   for stability and subtags required 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 3.2.  Stability
   provisions are described in Section 3.3.

   This procedure MAY also be used to register or alter the information
   for the "Description", "Comments", "Deprecated", or "Prefix" fields
   in a subtag's record as described in Figure 8. 9.  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 requster filling out the registration
   form reproduced below.  Note that each response is not limited in
   size and should take so that the room necessary to 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 6 7

   The subtag registration form MUST be sent to
   <ietf-languages@iana.org> for a two week review period before it can
   be submitted to IANA.  (This is an open list.  Requests to be added
   should list and can be sent joined by
   sending a request to <ietf-languages-request@iana.org>.)

   Variant and extlang subtags are always registered for use with a
   particular range of language tags.  For example, the subtag 'scouse'
   is intended for use with language tags that start with the primary
   language subtag "en", since Scouse is a dialect of English.  Thus the
   subtag 'scouse' could be included in tags such as "en-Latn-scouse" or
   "en-GB-scouse".  This information is stored in the "Prefix" field in
   the registry.  Variant registration requests are REQUIRED to include
   at least one "Prefix" field in the registration form.

   The 'Prefix' field for a given registered subtag will be maintained
   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 should 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 SHOULD be proposed instead.

   The 'Description' field must MUST contain a description of the tag being
   registered written or transcribed into the Latin script; it may MAY also
   include a description in a non-Latin script.  Non-ASCII characters
   must
   MUST be escaped using the syntax described in Section 3.1.  The
   'Description' field is used for identification purposes and should
   not be taken to 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 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 may have an impact on the provisions
   in Section 3.3.

   The Language Subtag Reviewer is responsible for responding to
   requests for the registration of subtags through the registration
   process  and is appointed by the IESG.

   When the two week period has passed the Language Subtag Reviewer
   either forwards the record to be inserted or modified to
   iana@iana.org according to the procedure described in Section 3.2, or
   rejects the request because of significant objections raised on the
   list or due to problems with constraints in this document (which
   should MUST
   be explicitly cited).  The reviewer may MAY also extend the review period
   in two week increments to permit further discussion.  The reviewer must
   MUST indicate on the list whether the registration has been accepted,
   rejected, or extended following each two week period.

   Note that the reviewer can raise objections on the list if he or she
   so desires.  The important thing is that the objection must MUST be made
   publicly.

   The applicant is free to modify a rejected application with
   additional information and submit it again; this restarts the two
   week comment period.

   Decisions made by the reviewer may MAY be appealed to the IESG [RFC 2028]
   [9] under the same rules as other IETF decisions [RFC 2026] [8].

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

   Updates or changes to existing records, including previous
   registrations, 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 "Description" in the registration form is
   intended as an aid to people trying to verify 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 MAY be appropriate.  The subtag reviewer decides what
   constitutes "good enough" reference material.  This requirement is
   not intended to exclude particular languages or dialects due to the
   size of the speaker population or lack of a standardized orthography.
   Minority languages will be considered equally on their own merits.

3.5  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 can 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.  No language subtags will be registered for codes
      that exist in ISO 639-1 or ISO 639-2, which are under
      consideration by the ISO 639 maintenance or registration
      authorities, or which have never been attempted for registration
      with those authorities.  If ISO 639 has previously rejected a
      language for registration, it is reasonable to assume that there
      must be additional very compelling evidence of need before it will
      be registered in the IANA registry (to the extent that it is very
      unlikely that any subtags will be registered of this type).

   o  Dialect or other divisions or variations within a language, its
      orthography, writing system, regional or historical usage,
      transliteration or other transformation, or distinguishing
      variation may MAY be registered as variant subtags.  An example is the
      'scouse' subtag (the Scouse dialect of English).

   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 3.3.  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.

   This document leaves the decision on what subtags  or changes to
   subtags are appropriate (or not) to the registration process
   described in Section 3.4.

   Note: four character primary language subtags are reserved to allow
   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

   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
   reached at:

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

   Fax: +1-212-963-0623
   E-mail: statistics@un.org
   URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm

3.6  Extensions and Extensions Namespace

   Extension subtags are those introduced by single-letter subtags other
   than 'x'.  They are reserved for the generation of identifiers which
   contain a language component, and are compatible with applications
   that understand language tags.  For example, they might be used to
   define locale identifiers, which are generally based on language.

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

   Allocation of a single-letter subtag shall SHALL take the form of an RFC
   defining the name, purpose, processes, and procedures for maintaining
   the subtags.  The maintaining or registering authority, including
   name, contact email, discussion list email, and URL location of the
   registry must 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.

   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.

   o  Modified the latin-script requirement on the 'Description' field
      so that "at least one Description field" must contain a Latin
      transcription.  (A.Phillips)

   IANA will maintain a registry of allocated single-letter (singleton)
   subtags.  This registry will 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 MUST forward this
   registration form to iesg@ietf.org, who will forward the request to
   iana@iana.org.  The maintaining authority of the extension MUST
   maintain the accuracy of the record by sending an updated full copy
   of the record to iana@iana.org with the subject line "LANGUAGE TAG
   EXTENSION UPDATE" whenever content changes.  Only the 'Comments',
   'Contact_Email', 'Mailing_List', and 'URL' fields may MAY be modified in
   these updates.

   Failure to maintain this record, the corresponding registry, or meet
   other conditions imposed by this section of this document may MAY be
   appealed to the IESG [RFC 2028] [9] under the same rules as other
   IETF decisions (see [8]) and may MAY result in the authority to maintain
   the extension being withdrawn or reassigned by the IESG.

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

    Figure 7: 8: Format of Records in the Language Tag Extensions Registry

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

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

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

   'Added' contains the date the RFC was published in the "full-date"
   format specified in RFC 3339 [14]. [15].  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
   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 may sometimes exist in common protocols where the extension is used.
   In particular, applications may 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, it should be noted note that some protocols may
   MAY impose upper limits on the length of the strings used to store or
   transport the language tag.

3.7  Initialization of the Registry

   Upon publication of this document as a BCP, the Language Subtag
   Registry must MUST be created and populated with the initial set of
   subtags.  This includes converting the entries from the existing IANA
   language tag registry defined by RFC 3066 to the new format.  This
   section defines the process for defining the new registry and
   performing the conversion of the old registry.

   The impact on the IANA maintainers of the registry of this conversion
   will be a small increase in the frequency of new entries.  The
   initial set of records represents no impact on IANA, since the work
   to create it will be performed externally (as defined in this
   section).  Future work will be limited to inserting or replacing
   whole records preformatted for IANA by the Language Subtag Reviewer.

   The initial registry will be created by the LTRU working group.
   Using the instructions in this document, the working group will
   prepare an Informational RFC by creating a series of Internet-Drafts
   containing the prototype registry according to the rules in Sections
   4.2.2 and 4.2.3 and subject to IESG review as described in Section
   6.1.1 of RFC 2026 [8].

   When the Internet-Draft containing the prototype registry has been
   approved by the IESG for publication as an RFC, the document will be
   forwarded to IANA, which will post the contents of the new registry
   on-line.

   Tags in the RFC 3066 registry that are not deprecated that consist
   entirely of subtags that are valid under this document and which have
   the correct form and format for tags defined by this document are
   superseded by this document.  Such tags are placed in records of type
   'redundant' in the registry.  For example, "zh-Hant" is now defined
   by this document.

   All other tags in the RFC 3066 registry that are deprecated will be
   maintained as grandfathered entries.  The record for the
   grandfathered entry will contain a 'Deprecated' field with the most
   appropriate date that can be determined for when the record was
   deprecated.  The 'Comments' field will contain the reason for the
   deprecation.  The 'Preferred-Value' field will contain the tag that
   replaces the value.  For example, the tag "art-lojban" is deprecated
   and will be placed in the grandfathered section.  It's 'Deprecated'
   field will contain the deprecation date (in this case "2003-09-02")
   and the 'Preferred-Value' field the value "jbo".

   Tags that are not deprecated and which contain subtags which are
   consistent with registration under the guidelines in this document
   will not automatically have a new subtag registration created for
   each eligible subtag.  Interrested parties may MAY use the registration
   process in Section 3.4 to register these subtags.  If all of the
   subtags in the original tag become fully defined by the resulting
   registrations, then the original tag is superseded by this document.
   Such tags will have their record changed from type 'grandfathered' to
   type 'redundant' in the registry.  For example, the subtag 'boont'
   could be registered, resulting in the change of the grandfathered tag
   "en-boont" to type redundant in the registry.

   Tags that contain one or more subtags that do not match the valid
   registration pattern and which are not otherwise defined by this
   document will have records of type  'grandfathered' created in the
   registry.  These records cannot become type 'redundant', but may MAY have
   a 'Deprecated' and 'Prefered-Value' field added to them if a subtag
   assignment or combination of assignments renders the tag obsolete.

   There will MUST be a reasonable period in which the community may can comment
   on the proposed list entries, which SHALL be no less than four weeks
   in length.  At the completion of this period, the chair(s) will
   notify iana@iana.org and the ltru and ietf-languages mail lists that
   the task is complete and forward the necessary materials to IANA for
   publication.

   Registrations that are in process under the rules defined in RFC 3066
   MAY be completed under the former rules, at the discretion of the
   language tag reviewer.  Any new registrations submitted after the
   request for conversion of the registry MUST be rejected.

   All existing RFC 3066 language tag registrations will be maintained
   in perpetuity.

   Users of tags that are grandfathered should SHOULD consider registering
   appropriate subtags in the IANA subtag registry (but are not required NOT REQUIRED
   to).

   UN numeric codes assigned to 'macro-geographical (continental)' or
   sub-regions not associated with an assigned ISO 3166 alpha-2 code are
   defined in the IANA registry and are valid for use in language tags.
   These codes MUST be added to the initial version of the registry.
   The UN numeric codes for 'economic groupings' or 'other groupings',
   and the alphanumeric codes in Appendix X of the UN document MUST NOT
   be added to the registry.

   When creating records for ISO 639, ISO 15924, ISO3166, and UN M.49
   codes, the following criteria SHALL be applied to the inclusion,
   preferred value, and deprecation of codes:

   For each standard, the date of the standard referenced in RFC 1766 is
   selected as the starting date.  Codes that were valid on that date in
   the selected standard are added to the registry.  Codes that were
   previously assigned by but which were vacated or withdrawn before
   that date are not added to the registry.  For each successive change
   to the standard, any additional assignments are added to the
   registry.  Values that are withdrawn are marked as deprecated, but
   not removed.  Changes in meaning or assignment of a subtag are
   permitted during this process (for example, the ISO 3166 code 'CS'
   was originally assigned to 'Czechoslovakia' and is now assigned to
   'Serbia and Montenegro').  This continues up to the date that this
   document was adopted.  The resulting set of records is added to the
   registry.  Future changes or additions to this portion of the
   registry are governed by the provisions of this document.

4.  Formation and Processing of Language Tags

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

4.1  Choice of Language Tag

   One may occasionally be 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.

   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 may 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 RFC 3066 [23] [24] 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 should 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 generally
   not 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 and are reserved for future standardization.  Applications
   may
   might benefit from their judicious use in forming language tags in
   the
   future and similar future.  Similar recommendations are expected to apply to their
   use as apply to script subtags.

   Standards, protocols and applications that reference this document
   normatively but apply different rules to the ones given in this
   section MUST specify how the procedure varies from the one given
   here.

   The choice of subtags used to form a language tag should 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 which script subtags 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 may might be appropriate to choose to indicate
          both scripts to aid in content selection, such as the
          application of a stylesheet.

   3.  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'.

   4.  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 MAY be useful
       for protocols that require a language tag to be provided.  The
       'und' subtag may MAY also be useful when matching language tags in
       certain situations.

   5.  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 SHOULD individually tag the
       languages where they appear or otherwise indicate the actual
       language in preference to the 'mul' subtag.

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

       *  For example, do not use "en-GB-scouse-scouse".

   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 language tag always defines a language as spoken (or written,
   signed or otherwise signaled) by human beings for communication of
   information to other human beings.  Computer languages such as
   programming languages are explicitly excluded.

   If a language tag B contains language tag A as a prefix, then B is
   typically "narrower" or "more specific" than A. For example, "zh-
   Hant-TW" is more specific than "zh-Hant".

   This relationship is not guaranteed in all cases: specifically,
   languages that begin with the same sequence of subtags are NOT
   guaranteed to be mutually intelligible, although they may 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 may 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.

   The relationship between the tag and the information it relates to is
   defined by the standard describing the context in which it appears.
   Accordingly, this section can only give possible examples of its
   usage.

   o  For a single information object, the associated language tags
      might be interpreted as the set of languages that is required 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
      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.

4.3  Canonicalization of Language Tags

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

   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.

   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 are either 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-NH" (English as used in the New
   Hebrides) is not canonical because the 'NH' subtag has a canonical
   mapping to 'VU' (Vanuatu), although the tag "en-NH" 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
   optionally
   regularize the case of the subtags, 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;
   lowercase everything else.

   Note: Case folding of ASCII letters in certain locales, unless
   carefully handled, may produce 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 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 may exist between the
   various subtags in the extension and thus MAY define an alternate
   canonicalization scheme for the extension's subtags.  Extensions MAY
   define how the order of the extension's subtags are interpreted.  For
   example, an extension could define that its subtags are in canonical
   order when the subtags are placed into ASCII order: that is, "en-a-
   aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa".  Another extension might
   define that the order of the subtags influences their semantic
   meaning (so that "en-b-ccc-bbb-aaa" has a different value from "en-b-
   aaa-bbb-ccc").  However, extension specifications SHOULD be designed
   so that they are tolerant of the typical processes described in
   Section 3.6.

4.4  Considerations for Private Use Subtags

   Private-use subtags require private agreement between the parties
   that intend to use or exchange language tags that use them and great
   caution should SHOULD be used in employing them in content or protocols
   intended for general use.  Private-use subtags are simply useless for
   information exchange without prior arrangement.

   The value and semantic meaning of private-use tags and of the subtags
   used within such a language tag are not defined by this document.

   The use of 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 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 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 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 may depend sometimes depends on the
   particular domain in question.

5.  IANA Considerations

   This section deals with the processes and requirements necessary for
   IANA to undertake to maintain the rsubtag and extension registries as
   defined by this document and in accordance with the requirements of
   RFC 2434 [11].

   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.

   Upon adoption of this document, the process described in Section 3.7
   will be used to generate the initial Language Subtag Registry.  The
   initial set of records represents no impact on IANA, since the work
   to create it will be performed externally (as defined in that
   section).  The new registry will be listed under "Language Tags" at
   <http://www.iana.org/numbers.html>.  The existing directory of
   registration forms and RFC 3066 registrations will be relabeled as
   "Language Tags (Obsolete)" and maintained (but not added to or
   modified).

   Future work on the Language Subtag Registry will be limited to
   inserting or replacing whole records preformatted for IANA by the
   Language Subtag Reviewer as described in Section 3.2 of this
   document.  Each record will be sent to iana@iana.org with a subject
   line indicating whether the enclosed record is an insertion (of a new
   record) or a replacment of an existing record which has a Type and
   Subtag (or Tag) field that exactly matches the record sent.  Records
   cannot be deleted from the registry.

   The Language Tag Extensions registry will also be generated and sent
   to IANA as described in Section 3.6.  This registry may can contain at
   most 35 records and thus changes to this registry are expected to be
   very infrequent.

   Future work by IANA on the Language Tag Extensions Registry is
   limited to two cases.  First, the IESG may MAY request that new records
   be inserted into this registry from time to time.  These requests
   will include the record to insert in the exact format described in
   Section 3.6.  In addition, there may 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.

6.  Security Considerations

   Language tags used in content negotiation, like any other information
   exchanged on the Internet, may might be a source of concern because they
   may
   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,
   RFC  3552 [15] [16] for best current practice guidance on security threats
   and defenses).

   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 Section 2.1.1 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 3.6) MUST be available over the Internet, implementations
   SHOULD NOT mechanically depend on it being always accessible, to
   prevent denial-of-service attacks.

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 may can 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.

8.  Changes from RFC 3066

   The main goals for this revision of language tags were the following:

   *Compatibility.* All valid RFC 3066 language tags  (including those
   in the IANA registry)  remain valid in this specification.  Thus
   there is complete backward compatibility of this specification with
   existing content.  In addition, this document defines language tags
   in such as way as to ensure future compatibility, and processors
   based solely on the RFC 3066 ABNF (such as those described in XML
   Schema version 1.0 [19]) [20]) will be able to process tags described by
   this document.

   *Stability.* Because of the changes in underlying ISO standards, a
   valid RFC 3066 language tag may become invalid (or have its meaning
   change) at a later date.  With so much of the world's computing
   infrastructure dependent on language tags, this is simply
   unacceptable: it invalidates content that may have an extensive
   shelf-life.  In this specification, once a language tag is valid, it
   remains valid forever.  Previously, there was no way to determine
   when two tags were equivalent.  This specification provides a stable
   mechanism for doing so, through the use of canonical forms.  These
   are also stable, so that implementations can depend on the use of
   canonical forms to assess equivalency.

   *Validity.*  The structure of language tags defined by this document
   makes it possible to determine if a particular tag is well-formed
   without regard for the actual content or "meaning" of the tag as a
   whole.  This is important because the registry and underlying
   standards  change over time.  In addition, it must be possible to
   determine if a tag is valid (or not) for a given point in time in
   order  to provide reproducible, testable results.  This process must
   not be error-prone; otherwise even intelligent people will generate
   implementations that give different results.  This specification
   provides for that by having a single data file, with specific
   versioning information, so that the validity of language tags at any
   point in time can be precisely determined (instead of interpolating
   values from many separate sources).

   *Extensibility.* It is important to be able to differentiate between
   written forms of language -- for many implementations this is more
   important than distinguishing between spoken variants of a language.
   Languages are written in a wide variety of different scripts, so this
   document provides for the generative use of ISO 15924 script codes.
   Like the generative use of ISO language and country codes in RFC
   3066, this allows combinations to be produced without resorting to
   the registration process.  The addition of UN codes provides for the
   generation of language tags with regional scope, which is also
   required for information technology.

   The recast of the registry from containing whole language tags to
   subtags is a key part of this.  An important feature of RFC 3066 was
   that it allowed generative use of subtags.  This allows people to
   meaningfully use generated tags, without the delays in registering
   whole tags, and the burden on the registry of having to supply all of
   the combinations that people may find useful.

   Because of the widespread use of language tags, it is potentially
   disruptive to have periodic revisions of the core specification,
   despite demonstrated need.  The extension mechanism provides for a
   way for independent RFCs to define extensions to language tags.
   These extensions have a very constrained, well-defined structure to
   prevent extensions from interfering with implementations of language
   tags defined in this document.  The document also anticipates
   features of ISO 639-3 with the addition of the extended language
   subtags, as well as the possibility of other ISO 639 parts becoming
   useful for the formation of language tags in the future.  The use and
   definition of private use tags has also been modified, to allow
   people to move as much information as possible out of private use
   tags, and into the regular structure.  The goal is to dramatically
   reduce the need to produce a revision of this document in the future.

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

   o  Defines the ABNF and rules for subtags so that the category of all
      subtags can be determined without reference to the registry.

   o  Adds the concept of well-formed vs. validating processors,
      defining the rules by which an implementation can claim to be one
      or the other.

   o  Replaces the IANA language tag registry with a language subtag
      registry that provides a complete list of valid subtags in the
      IANA registry.  This allows for robust implementation and ease of
      maintenance.  The language subtag registry becomes the canonical
      source for forming language tags.

   o  Provides a process that guarantees stability of language tags, by
      handling reuse of values by ISO 639, ISO 15924, and ISO 3166 in
      the event that they register a previously used value for a new
      purpose.

   o  Allows ISO 15924 script code subtags and allows them to be used
      generatively.  Defines a method for indicating in the registry
      when script subtags are necessary for a given language tag.

   o  Adds the concept of a variant subtag and allows variants to be
      used generatively.

   o  Adds the ability to use a class of UN M.49 tags for  supra-
      national regions and to resolve conflicts in the assignment of ISO
      3166 codes.

   o  Defines the private-use tags in ISO 639, ISO 15924, and ISO 3166
      as the mechanism for creating private-use language, script, and
      region subtags respectively.

   o  Adds a well-defined extension mechanism.

   o  Defines an extended language subtag, possibly for use with certain
      anticipated features of ISO 639-3.

   Ed Note: The following items are provided for the convenience of
   reviewers and will be removed from the final document.

   Changes between draft-ietf-ltru-registry-02 and this version are:

   o  Modified the title and some of the front matter of Section 3.7
      from "Conversion of the RFC 3066 Language Tag Registry"
      (A.Phillips)

   o  Modified the rules for registry creation so that no variant
      registrations are created ab initio. (#922) (J.Cowan)

   o  Modified the document to replace 'Canonical' with 'Preferred-
      Value' and to implement the various design changes necessary to
      deal with canonicalization. (#954) (F.Ellermann, A.Phillips, et
      al)

   o  Corrected the ABNF so that 'lang' is defined as 2*4ALPHA (J.Cowan)

   o  Changed the requirement in Section 2.1.1 on truncation of tags
      from MUST to SHOULD and added a sentence about the harm this may
      cause.  (F.Ellermann, D.Ewell)

   o  Changed "MUST be very compelling" to "must (etc.)" in Section 3.5.
      (R.Presuhn)

   o  Changed "STRONGLY RECOMMENDED" to "strongly RECOMMENDED"
      (R.Presuhn)

   o  Added sentences pertaining to the File-Date record to Section 3.1.
      (#941) (R.Presuhn)
   o  Changed the process by which the prototype registry is created
      from a mere document to an Informational RFC. (#838, #835) (??)

   o  Changed the Security Considerations (Section 6) and Length
      Considerations (Section 2.1.1) sections to address potential
      buffer overflow attacks and suggest a lower limit on buffer length
      allocation (#944)(#965) (R.Presuhn, I.McDonald)

   o  Clarified a sentence in Security Considerations (Section 6) to
      make clear that it refers to extensions and not the language
      subtag registry. (#965) (I.McDonald)

   o  Added the limitation in the ABNF on the number of extlang subtags
      (limited to three) (#965) (R.Presuhn, A.Phillips)

   o  Added notes to extlang and variant explaining that they should be
      used with their Recommended-Prefixes.  (A.Phillips)

   o  Changed the name of the 'Recommended-Prefix' field to 'Prefix' and
      the requirements for validating processors to require the prefix
      with variants and extlangs. (#1018) (J.Cowan, F.Ellerman)

   o  Added notes about when variants may be used together and the
      relationship of the 'Prefix' field to this in Section 2.2.5
      (A.Phillips)

   o  Specified that 'Prefix' fields may be added only to 'variant'
      subtag records and not to 'extlang' records.  (J.Cowan)

   o  Converted lowercase RFC 2119 words to their RFC 2119 normative
      equivalent.  A few exceptions remain (where the words functioned
      in a non-normative fashion).  (I.McDonald)

   o  Rewrote Section 2.1.1 so that it deals with a canonical minimum
      maximum length, etc. (#944)

9.  References

9.1  Normative References

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

   [2]   International Organization for Standardization, "ISO 639-2:1998
         - Codes for the representation of names of languages -- Part 2:
         Alpha-3 code - edition 1", August 1988.

   [3]   ISO TC46/WG3, "ISO 15924:2003 (E/F) - Codes for the
         representation of names of scripts", January 2004.

   [4]   International Organization for Standardization, "Codes for the
         representation of names of countries, 3rd edition",
         ISO Standard 3166, August 1988.

   [5]   Statistical Division, United Nations, "Standard Country or Area
         Codes for Statistical Use", UN Standard Country or Area Codes
         for Statistical Use, Revision 4 (United Nations publication,
         Sales No. 98.XVII.9, June 1999.

   [6]   International Organization for Standardization, "ISO/IEC 10646-
         1:2000. Information technology -- Universal Multiple-Octet
         Coded Character Set (UCS) -- Part 1: Architecture and Basic
         Multilingual Plane and ISO/IEC 10646-2:2001. Information
         technology -- Universal Multiple-Octet Coded Character Set
         (UCS) -- Part 2: Supplementary Planes, as, from time to time,
         amended, replaced by a new edition or expanded by the addition
         of new parts", 2000.

   [7]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
         Specifications: ABNF", draft-crocker-abnf-rfc2234bis-00 (work
         in progress), March 2005.

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

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

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

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

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

   [13]  Carpenter, B., Baker, F., and M. Roberts, "Memorandum of
         Understanding Concerning the Technical Work of the Internet
         Assigned Numbers Authority", RFC 2860, June 2000.

   [14]  Resnick, P., "Internet Message Format", RFC 2822, April 2001.

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

   [15]

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

9.2  Informative References

   [16]

   [17]  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>.

   [17]

   [18]  Raymond, E., "The Art of Unix Programming", 2003.

   [18]

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

   [19]

   [20]  Biron, P., Ed. and A. Malhotra, Ed., "XML Schema Part 2:
         Datatypes Second Edition", 10 2004, <
         http://www.w3.org/TR/xmlschema-2/>.

   [20]

   [21]  Unicode Consortium, "The Unicode Consortium. The Unicode
         Standard, Version 4.1.0, defined by: The Unicode Standard,
         Version 4.0 (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-
         18578-1), as amended by Unicode 4.0.1
         (http://www.unicode.org/versions/Unicode4.0.1) and by Unicode
         4.1.0 (http://www.unicode.org/versions/Unicode4.1.0).",
         March 2005.

   [21]

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

   [22]

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

   [23]

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

Authors' Addresses

   Addison Phillips (editor)
   Quest Software

   Email: addison.phillips@quest.com

   Mark Davis (editor)
   IBM

   Email: mark.davis@us.ibm.com

Appendix A.  Acknowledgements

   Any list of contributors is bound to be incomplete; please regard the
   following as only a selection from the group of people who have
   contributed to make this document what it is today.

   The contributors to RFC 3066 and RFC 1766, the precursors of this
   document, made enormous contributions directly or indirectly to this
   document and are generally responsible for the success of language
   tags.

   The following people (in alphabetical order) contributed to this
   document or to RFCs 1766 and 3066:

   Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet,
   Nathaniel Borenstein, Eric Brunner, Sean M. Burke, M.T. Carrasco
   Benitez, Jeremy Carroll, John Clews, Jim Conklin, Peter Constable,
   John Cowan, Mark Crispin, Dave Crocker, Martin Duerst, Frank
   Ellerman, Michael Everson, Doug Ewell, Ned Freed, Tim Goodwin, Dirk-
   Willem van Gulik, Marion Gunn, Joel Halpren, Elliotte Rusty Harold,
   Paul Hoffman, Scott Hollenbeck, Richard Ishida, Olle Jarnefors, Kent
   Karlsson, John Klensin, Alain LaBonte, Eric Mader, Ira McDonald,
   Keith Moore, Chris Newman, Masataka Ohta, Randy Presuhn, George
   Rhoten, Markus Scherer, Keld Jorn Simonsen, Thierry Sourbier, Otto
   Stolz, Tex Texin, Andrea Vine, Rhys Weatherley, Misha Wolf, Francois
   Yergeau and many, many others.

   Very special thanks must go to Harald Tveit Alvestrand, who
   originated RFCs 1766 and 3066, and without whom this document would
   not have been possible.  Special thanks must go to Michael Everson,
   who has served as language tag reviewer for almost the complete
   period since the publication of RFC 1766.  Special thanks to Doug
   Ewell, for his production of the first complete subtag registry, and
   his work in producing a test parser for verifying language tags.

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 Simlified script as used in
      mainland China)

      sr-Latn-CS (Serbian written using the Latin script as used in
      Serbia and Montenegro)

   Language-Variant:

      en-boont (Boontling dialect of English)

      en-scouse (Scouse dialect of English)

   Language-Region-Variant:

      en-GB-scouse (Scouse dialect of English as used in the UK)

   Language-Script-Region-Variant:

      sl-Latn-IT-nedis (Nadiza dialect of Slovenian written using the
      Latin script as used in Italy.  Note that this tag is not
      recommended 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 for 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 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-CS (Serbian, private script, for Serbia and Montenegro)

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

      en-US-u-islamCal

      zh-CN-a-myExt-x-private

      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)

Appendix C.  Example Registry

   Example Registry

   File-Date: 2005-04-18
   %%
   Type: language
   Subtag: aa
   Description: Afar
   Added: 2004-07-06
   %%
   Type: language
   Subtag: ab
   Description: Abkhazian
   Added: 2004-07-06
   %%
   Type: language
   Subtag: ae
   Description: Avestan
   Added: 2004-07-06
   %%
   Type: language
   Subtag: ar
   Description: Arabic
   Added: 2004-07-06
   Suppress-Script: Arab
   Comment: Arabic text is usually written in Arabic script
   %%
   Type: language
   Subtag: qaa..qtz
   Description: PRIVATE USE
   Added: 2004-08-01
   Comment: Use private use codes in preference
     to the x- singleton for primary language
   Comment: This is an example of two comments.
   %%
   Type: script
   Subtag: Arab
   Description: Arabic
   Added: 2004-07-06
   %%
   Type: script
   Subtag: Armn
   Description: Armenian
   Added: 2004-07-06
   %%
   Type: script
   Subtag: Bali
   Description: Balinese
   Added: 2004-07-06
   %%
   Type: script
   Subtag: Batk
   Description: Batak
   Added: 2004-07-06
   %%
   Type: region
   Subtag: AA
   Description: PRIVATE USE
   Added: 2004-08-01
   %%
   Type: region
   Subtag: AD
   Description: Andorra
   Added: 2004-07-06
   %%
   Type: region
   Subtag: AE
   Description: United Arab Emirates
   Added: 2004-07-06
   %%
   Type: region
   Subtag: AX
   Description: &#xC5;land Islands
   Added: 2004-07-06
   Comments: The description shows a Unicode escape
     for the letter A-ring.
   %%
   Type: region
   Subtag: 001
   Description: World
   Added: 2004-07-06
   %%
   Type: region
   Subtag: 002
   Description: Africa
   Added: 2004-07-06
   %%
   Type: region
   Subtag: 003
   Description: North America
   Added: 2004-07-06
   %%
   Type: variant
   Subtag: 1901
   Description: Traditional German
      orthography
   Added: 2004-09-09
   Prefix: de
   Comment: <shows continuation>
   %%
   Type: variant
   Subtag: 1996
   Description: German orthography of 1996
   Added: 2004-09-09
   Prefix: de
   %%
   Type: variant
   Subtag: boont
   Description: Boontling
   Added: 2003-02-14
   Prefix: en
   %%
   Type: variant
   Subtag: gaulish
   Description: Gaulish
   Added: 2001-05-25
   Prefix: cel
   %%
   Type: grandfathered
   Tag: art-lojban
   Description: Lojban
   Added: 2001-11-11
   Canonical: jbo
   Deprecated: 2003-09-02
   %%
   Type: grandfathered
   Tag: en-GB-oed
   Description: English, Oxford English Dictionary spelling
   Added: 2003-07-09
   %%
   Type: grandfathered
   Tag: i-ami
   Description: 'Amis
   Added: 1999-05-25
   %%
   Type: grandfathered
   Tag: i-bnn
   Description: Bunun
   Added: 1999-05-25
   %%
   Type: redundant
   Tag: az-Arab
   Description: Azerbaijani in Arabic script
   Added: 2003-05-30
   %%
   Type: redundant
   Tag: az-Cyrl
   Description: Azerbaijani in Cyrillic script
   Added: 2003-05-30
   %%

                 Figure 8: 9: Example of the Registry Format

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