Network Working Group A. Phillips, Ed. Internet-Draft Quest Software Expires: November 20, 2005 M. Davis, Ed. IBM May 19, 2005 Tags for Identifying Languages draft-ietf-ltru-registry-02 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 20, 2005. 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). Phillips & Davis Expires November 20, 2005 [Page 1] Internet-Draft langtags-registry May 2005 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 2.2.1 Primary Language Subtag . . . . . . . . . . . . . . . 8 2.2.2 Extended Language Subtags . . . . . . . . . . . . . . 10 2.2.3 Script Subtag . . . . . . . . . . . . . . . . . . . . 10 2.2.4 Region Subtag . . . . . . . . . . . . . . . . . . . . 11 2.2.5 Variant Subtags . . . . . . . . . . . . . . . . . . . 12 2.2.6 Extension Subtags . . . . . . . . . . . . . . . . . . 13 2.2.7 Private Use Subtags . . . . . . . . . . . . . . . . . 14 2.2.8 Pre-Existing RFC 3066 Registrations . . . . . . . . . 15 2.2.9 Classes of Conformance . . . . . . . . . . . . . . . . 15 3. Registry Format and Maintenance . . . . . . . . . . . . . . . 17 3.1 Format of the IANA Language Subtag Registry . . . . . . . 17 3.2 Maintenance of the Registry . . . . . . . . . . . . . . . 21 3.3 Stability of IANA Registry Entries . . . . . . . . . . . . 23 3.4 Registration Procedure for Subtags . . . . . . . . . . . . 26 3.5 Possibilities for Registration . . . . . . . . . . . . . . 29 3.6 Extensions and Extensions Namespace . . . . . . . . . . . 31 3.7 Conversion of the RFC 3066 Language Tag Registry . . . . . 34 4. Formation and Processing of Language Tags . . . . . . . . . . 37 4.1 Choice of Language Tag . . . . . . . . . . . . . . . . . . 37 4.2 Meaning of the Language Tag . . . . . . . . . . . . . . . 39 4.3 Canonicalization of Language Tags . . . . . . . . . . . . 40 4.4 Considerations for Private Use Subtags . . . . . . . . . . 41 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43 6. Security Considerations . . . . . . . . . . . . . . . . . . . 44 7. Character Set Considerations . . . . . . . . . . . . . . . . . 45 8. Changes from RFC 3066 . . . . . . . . . . . . . . . . . . . . 46 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 50 9.1 Normative References . . . . . . . . . . . . . . . . . . . 50 9.2 Informative References . . . . . . . . . . . . . . . . . . 51 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 52 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 53 B. Examples of Language Tags (Informative) . . . . . . . . . . . 54 C. Example Registry . . . . . . . . . . . . . . . . . . . . . . . 57 Intellectual Property and Copyright Statements . . . . . . . . 61 Phillips & Davis Expires November 20, 2005 [Page 2] Internet-Draft langtags-registry May 2005 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 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]. Phillips & Davis Expires November 20, 2005 [Page 3] Internet-Draft langtags-registry May 2005 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. Phillips & Davis Expires November 20, 2005 [Page 4] Internet-Draft langtags-registry May 2005 The syntax of this tag in ABNF [7] is: Language-Tag = (lang *("-" extlang) ["-" script] ["-" region] *("-" variant) *("-" extension) ["-" privateuse]) / privateuse ; private-use tag / grandfathered ; grandfathered registrations lang = 2*3ALPHA ; shortest ISO 639 code / registered-lang extlang = 3ALPHA ; reserved for future use script = 4ALPHA ; ISO 15924 code region = 2ALPHA ; ISO 3166 code / 3DIGIT ; UN country number variant = 5*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 be only four characters long, while those starting with a letter 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 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 Phillips & Davis Expires November 20, 2005 [Page 5] Internet-Draft langtags-registry May 2005 the UTF-16LE [12] encoding of Unicode [20]. 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 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 the ABNF nor other guidelines in this document provide a fixed upper limit on the number of subtags in a Language Tag (and thus the upper bound on the size of a tag) and it is possible to envision quite long and complex subtag sequences, in practice these are rare because additional granularity in tags seldom adds useful distinguishing information and because longer, more granular tags interefere with the meaning, understanding, and processing of language tags. 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 a maximum length of 26 characters (excluding any extensions or private use sequences). This is because subtags are limited to a length of eight characters and the extlang, script, and region subtags are limited to even fewer characters. See Section 4.1 for more information on selecting the most appropriate Language Tag. A conformant implementation MAY refuse to support the storage of language tags which exceed a specified length. For an example, see Phillips & Davis Expires November 20, 2005 [Page 6] Internet-Draft langtags-registry May 2005 [RFC 2231] [22]. Any such limitation MUST 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. 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 Phillips & Davis Expires November 20, 2005 [Page 7] Internet-Draft langtags-registry May 2005 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. Phillips & Davis Expires November 20, 2005 [Page 8] Internet-Draft langtags-registry May 2005 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 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]: "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 Phillips & Davis Expires November 20, 2005 [Page 9] Internet-Draft langtags-registry May 2005 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 any additional number of 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. 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: Phillips & Davis Expires November 20, 2005 [Page 10] Internet-Draft langtags-registry May 2005 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 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: Phillips & Davis Expires November 20, 2005 [Page 11] Internet-Draft langtags-registry May 2005 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 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. Phillips & Davis Expires November 20, 2005 [Page 12] Internet-Draft langtags-registry May 2005 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 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. "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. 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 Phillips & Davis Expires November 20, 2005 [Page 13] Internet-Draft langtags-registry May 2005 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- Phillips & Davis Expires November 20, 2005 [Page 14] Internet-Draft langtags-registry May 2005 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 to express their level of conformance with the rules and practices described in this document. There are generally two classes of conforming implementations: "well-formed" processors and "validating" processors. Claims of conformance SHOULD explicitly reference one of these definitions. An implementation that claims to check for well-formed language tags MUST: o Check that the tag and all of its subtags, including extension and private-use subtags, conform to the ABNF or that the tag is on the list of grandfathered tags. o Check that singleton subtags that identify extensions do not repeat. For example, the tag "en-a-xx-b-yy-a-zz" is not well- formed. Well-formed processors are strongly encouraged to implement the 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. Phillips & Davis Expires November 20, 2005 [Page 15] Internet-Draft langtags-registry May 2005 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 If the processor generates tags, it MUST do so in canonical form, including any supported extensions, as defined in Section 4.3. Phillips & Davis Expires November 20, 2005 [Page 16] Internet-Draft langtags-registry May 2005 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]. 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 Phillips & Davis Expires November 20, 2005 [Page 17] Internet-Draft langtags-registry May 2005 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] (see ). 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 "€". Note that the hexadecimal notation may have between two and six digits. All fields whose field-body contains a date value use the "full-date" format specified in RFC 3339 [14]. 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" and whose field-body contains the last modification date of the registry: 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". Phillips & Davis Expires November 20, 2005 [Page 18] Internet-Draft langtags-registry May 2005 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 contain a description of the tag being registered written or transcribed into the Latin script; the same or additional fields may also include a description in a non- Latin script. The 'Description' field is used for identification purposes and should not be taken to represent the actual native name of the language or variation or to be in any particular language. 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 Canonical * For fields of type 'language', 'extlang', 'script', 'region', and 'variant', a canonical mapping of this record to a subtag record of the same 'Type'. * For fields of type 'grandfathered' and 'redundant', a canonical mapping to a complete language tag. Phillips & Davis Expires November 20, 2005 [Page 19] Internet-Draft langtags-registry May 2005 o Deprecated * Deprecated's field-value contains the date the record was deprecated. o Recommended-Prefix * Recommended-Prefix's field-value contains a language tag with which this subtag may be used to form a new language tag, perhaps with other subtags as well. This field MUST only appear in records whose 'Type' field-value is 'variant' or 'extlang'. For example, the 'Recommended-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 'Canonical' SHALL NOT be added to any record already in the registry. The field 'Canonical' SHALL NOT be modified except for records of type "grandfathered": therefore a subtag whose record contains no canonical mapping when the record is created is a canonical form and will remain so. The 'Canonical' 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'. Note that a record that has a 'Canonical' field MUST have a 'Deprecated' field also (although the converse is not true). The field 'Deprecated' MAY be added to any record via the maintenance process described in Section 3.2 or via the registration process Phillips & Davis Expires November 20, 2005 [Page 20] Internet-Draft langtags-registry May 2005 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 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 'Canonical' field has no replacement mapping. The field 'Recommended-Prefix' MAY appear more than once per record. Additional fields of this type MAY be added to a record via the registration process. The field-value of of this field consists of a language tag that is RECOMMENDED for use as a prefix for this subtag. For example, the variant subtag 'scouse' has a recommended prefix of "en". This means that tags starting with the prefix "en-" are most appropriate with this subtag, so "en-Latn-scouse" and "en-GB-scouse" are both acceptable, while the tag "fr-scouse" is probably an inappropriate choice. The field of type Recommended-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 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 new codes are assigned by ISO 639, ISO 15924, and ISO 3166, the Language Subtag Reviewer Phillips & Davis Expires November 20, 2005 [Page 21] Internet-Draft langtags-registry May 2005 will evaluate each assignment, determine whether it conflicts with existing registry entries, and submit the information to IANA for inclusion in the registry. If an assignment takes place and the Language Subtag Reviewer does not do this in a timely manner, then any interested party may use the procedure in Section 3.4 to register the appropriate update. Note: The redundant and grandfathered entries together are the complete list of tags registered under RFC 3066 [23]. 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 items in both lists are permanent and stable, although grandfathered items may be deprecated over time. Refer to 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, 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 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 Recommended-Prefix: sl Comments: This is a comment shown as an example. %% Figure 4 Phillips & Davis Expires November 20, 2005 [Page 22] Internet-Draft langtags-registry May 2005 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] "full-date" format. Values in the 'Subtag' field 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 and that the choice of language tag for specific content is also stable over time. 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' and 'Canonical' 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 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 'Recommended-Prefix' MAY be added via the registration process. o Values in the field 'Recommended-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", "fr", or "en-US-boont". o Values in the field 'Recommended-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. Phillips & Davis Expires November 20, 2005 [Page 23] Internet-Draft langtags-registry May 2005 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. The registration process MAY be used to add a note indicating the withdrawal of the code by the respective standard. o Codes assigned by ISO 639, ISO 15924, or ISO 3166 that do not conflict with existing subtags of the associated type but which represent the same meaning as an existing subtag of that type are entered into the IANA registry as new records. The field 'canonical value' for that record MUST contain the existing subtag of the same meaning Example If ISO 3166 were to assign the code 'IM' to represent the value "Isle of Man" (represented in the IANA registry by the UN M.49 code '833'), '833' remains the canonical subtag and 'IM' would be assigned '833' as a canonical value. This prevents tags that are in canonical form from becoming non-canonical. Example If the tag 'enochian' were registered as a primary language subtag and ISO 639 subsequently assigned an alpha-3 code to the same language, the new ISO 639 code would be entered into the IANA registry as a subtag with a canonical mapping to 'enochian'. The new ISO code can be used, but it is not canonical. o Codes assigned by ISO 639, ISO 15924, or ISO 3166 that conflict with existing subtags of the associated type 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 prepare a proposal for entering in the IANA registry as soon as practical a registered language subtag as an alternate value for the new code. The form of the registered language subtag will be at the discretion of the Language Subtag Reviewer and must conform to other restrictions on language subtags in this document. Phillips & Davis Expires November 20, 2005 [Page 24] Internet-Draft langtags-registry May 2005 * 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 prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and must conform to other restrictions on variant subtags in this document. * 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 canonical entry 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 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 prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and must conform to other restrictions on variant subtags in this document. This situation is very unlikely to ever occur. o Stability provisions apply to grandfathered tags with this exception: should all of the subtags in a grandfathered tag become valid subtags in the IANA registry, then the grandfathered tag Phillips & Davis Expires November 20, 2005 [Page 25] Internet-Draft langtags-registry May 2005 MUST be marked as 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 for stability and subtags required 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 "Recommended- Prefix" fields in a subtag's record as described in Figure 7. 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 the room necessary to adequately describe the registration. The fields in the "Record Requested" section SHOULD follow the requirements in Section 3.1. Phillips & Davis Expires November 20, 2005 [Page 26] Internet-Draft langtags-registry May 2005 LANGUAGE SUBTAG REGISTRATION FORM 1. Name of requester: 2. E-mail address of requester: 3. Record Requested: Type: Subtag: Description: Recommended-Prefix: Canonical: Deprecated: Suppress-Script: Comments: 4. Intended meaning of the subtag: 5. Reference to published description of the language (book or article): 6. Any other relevant information: Figure 5 The subtag registration form MUST be sent to for a two week review period before it can be submitted to IANA. (This is an open list. Requests to be added should be sent to .) Variant subtags are generally registered for use with a particular 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 "Recommended-Prefix" field in the registry. Variant registration requests are REQUIRED to include at least one "Recommended-Prefix" field in the registration form. Any subtag MAY be incorporated into a variety of language tags, according to the rules of Section 2.1, including tags that do not match any of the recommended prefixes of the registered subtag. (Note that this is probably a poor choice.) This makes validation simpler and thus more uniform across implementations, and does not require the registration of a separate subtag for the same purpose and meaning but a different recommended prefix. The recommended prefixes for a given registered subtag will be maintained in the IANA registry as a guide to usage. If it is necessary to add an additional prefix to that list for an existing language tag, that can be done by filing an additional registration Phillips & Davis Expires November 20, 2005 [Page 27] Internet-Draft langtags-registry May 2005 form. In that form, the "Any other relevant information:" field should indicate that it is the addition of an additional recommended prefix. Requests to add a recommended prefix to a subtag that imply a different semantic meaning will probably be rejected. For example, a request to add the prefix "de" to the subtag 'nedis' so that the tag "de-nedis" represented some German dialect would be rejected. The 'nedis' subtag represents a particular Slovenian dialect and the additional registration would change the semantic meaning assigned to the subtag. A separate subtag should be proposed instead. The 'Description' field must contain a description of the tag being registered written or transcribed into the Latin script; it may also include a description in a non-Latin script. Non-ASCII characters must be escaped using the syntax described in Section 3.1. The 'Description' field is used for identification purposes and should not be taken to represent the actual native name of the language or variation or to be in any particular language. While the 'Description' field itself is not guaranteed to be stable and errata corrections may be undertaken from time to time, attempts to provide translations or transcriptions of entries in the registry itself will probably be frowned upon by the community or rejected outright, as changes of this nature may impact 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 be explicitly cited). The reviewer may also extend the review period in two week increments to permit further discussion. The reviewer 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 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. Phillips & Davis Expires November 20, 2005 [Page 28] Internet-Draft langtags-registry May 2005 Decisions made by the reviewer 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 the canonical method of referring to a specific language or variant. This provision does not apply to grandfathered tags, which may become deprecated due to registration of subtags. For example, the tag "i-navajo" is deprecated in favor of the tag "nv", which consists of the single primary language subtag 'nv'. Note: The purpose of the "published 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 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 Phillips & Davis Expires November 20, 2005 [Page 29] Internet-Draft langtags-registry May 2005 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 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, recommended prefixes, comments, deprecation of obsolete items, 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 Phillips & Davis Expires November 20, 2005 [Page 30] Internet-Draft langtags-registry May 2005 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 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 take the form of an RFC defining the name, purpose, processes, and procedures for maintaining the subtags. The maintaining or registering authority, including name, contact email, discussion list email, and URL location of the registry must be indicated clearly in the RFC. The RFC MUST specify 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 Phillips & Davis Expires November 20, 2005 [Page 31] Internet-Draft langtags-registry May 2005 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 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 be modified in these updates. Failure to maintain this record, the corresponding registry, or meet Phillips & Davis Expires November 20, 2005 [Page 32] Internet-Draft langtags-registry May 2005 other conditions imposed by this section of this document may be appealed to the IESG [RFC 2028] [9] under the same rules as other IETF decisions (see [8]) and 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 6: 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 which letter to use, although the IESG may change the assignment when approving the RFC. 'Description' contains the name and description of the extension. 'Comments' is an optional field and may contain a broader description of the extension. 'Added' contains the date the RFC was published in the "full-date" format specified in RFC 3339 [14]. 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 Phillips & Davis Expires November 20, 2005 [Page 33] Internet-Draft langtags-registry May 2005 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 exist in common protocols where the extension is used. In particular, applications may truncate the subtags in doing matching or in fitting into limited lengths, so it is RECOMMENDED that the most significant information be in the most significant (left-most) subtags, and that the specification gracefully handle truncated subtags. When a language tag is to be used in a specific, known, protocol, it is RECOMMENDED that that the language tag not contain extensions not supported by that protocol. In addition, it should be noted that some protocols may impose upper limits on the length of the strings used to store or transport the language tag. 3.7 Conversion of the RFC 3066 Language Tag Registry Upon publication of this document as a BCP, the existing IANA language tag registry must be converted into the new subtag registry. This section defines the process for performing this conversion. 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. When this document is published, an email will be sent by the chair(s) of the LTRU working group to the LTRU and ietf-languages mail lists advising of the impending conversion of the registry. In that notice, the chair(s) will provide a URL whose referred content is the proposed IANA Language Subtag Registry following conversion. There will be a Last Call period of not less than four weeks for comments and corrections to be discussed on the ietf-languages@iana.org mail list. Changes as a result of comments will not restart the Last Call period. At the end of the period, the chair(s) will forward the URL to IANA, which will post the new registry on-line. Tags that are currently 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 Phillips & Davis Expires November 20, 2005 [Page 34] Internet-Draft langtags-registry May 2005 be determined for when the record was deprecated. The 'Comments' field will contain the reason for the deprecation. The 'Canonical' 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 and 'Canonical' field the value "jbo". Tags 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. Tags that are not deprecated and which contain subtags which are consistent with registration under the guidelines in this document will have a new subtag registration created for each eligible subtag. If all of the subtags in the original tag are fully defined by the resulting registrations or by this document, then the original tag is superseded by this document. Such tags are placed in the 'redundant' section of the registry. For example, "en-boont" will result in a new subtag 'boont' and the RFC 3066 registered tag "en-boont" placed in the redundant section of 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. There will be a reasonable period in which the community may 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 consider registering appropriate subtags in the IANA subtag registry (but are not required to). Where two subtags have the same meaning, the priority of which to Phillips & Davis Expires November 20, 2005 [Page 35] Internet-Draft langtags-registry May 2005 make canonical SHALL be the following: o As of the date of acceptance of this document as a BCP, if a code exists in the associated ISO standard and it is not deprecated or withdrawn as of that date, then it has priority. o Otherwise, the earlier-registered tag in the associated ISO standard has priority. 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, canonical mapping, 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 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 (cf. 'CS'). 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. Phillips & Davis Expires November 20, 2005 [Page 36] Internet-Draft langtags-registry May 2005 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 faced with several possible tags for the same body of text. Interoperability is best served when all users use the same language tag in order to represent the same language. If an application has requirements that make the rules here inapplicable, then that application risks damaging interoperability. 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 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] 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 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 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 benefit from their judicious use in forming language tags in the future and 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 be guided by the following rules: Phillips & Davis Expires November 20, 2005 [Page 37] Internet-Draft langtags-registry May 2005 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 be appropriate to choose to indicate both scripts to aid in content selection, such as the application of a stylesheet. 3. If a subtag has a 'Canonical' field in its registry entry, the canonical subtag SHOULD be used to form the language tag in preference to any of its aliases. * 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 be useful for protocols that require a language tag to be provided. The 'und' subtag may also be useful when matching language tags in certain situations. 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 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. Phillips & Davis Expires November 20, 2005 [Page 38] Internet-Draft langtags-registry May 2005 * 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. In addition, tags that are in canonical form will always be in canonical form. 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 be. For example, the tag "az" shares a prefix with both "az-Latn" (Azerbaijani written using the Latin script) and "az-Cyrl" (Azerbaijani written using the Cyrillic script). A person fluent in one script may not be able to read the other, even though the text might be identical. Content tagged as "az" most probably is written in just one script and thus might not be intelligible to a reader familiar with the other script. The relationship between the tag and the information it relates to is defined by the standard describing the context in which it appears. Accordingly, this section can only give possible examples of its usage. o For a single information object, the associated language tags might be interpreted as the set of languages that is required for 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 Phillips & Davis Expires November 20, 2005 [Page 39] Internet-Draft langtags-registry May 2005 inspect each of the alternatives in order to find its language or languages. In this case, the presence of multiple tags might not mean that one needs to be multi-lingual to get complete understanding of the document. Example: MIME multipart/ alternative. o In markup languages, such as HTML and XML, language information can be added to each part of the document identified by the markup structure (including the whole document itself). For example, one could write C'est la vie. inside a Norwegian document; the Norwegian-speaking user could then access a French-Norwegian dictionary to find out what the marked section meant. If the user were listening to that document through a speech synthesis interface, this formation could be used to signal the synthesizer to appropriately apply French text-to-speech pronunciation rules to that span of text, instead of applying the inappropriate Norwegian rules. 4.3 Canonicalization of Language Tags Since a particular language tag may be used in 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. None of the subtags in the language tag has a Canonical-Value mapping in the IANA registry (see Section 3.1). Subtags with a Canonical-Value mapping MUST be replaced with their mapping in order to canonicalize the tag. 3. 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). Canonicalization of language tags does not imply anything about the Phillips & Davis Expires November 20, 2005 [Page 40] Internet-Draft langtags-registry May 2005 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, 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 non-ASCII character values. The Unicode Character Database file "SpecialCasing.txt" defines the specific cases that are known to cause problems with this. In particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE). Implementers should specify a locale-neutral casing operation to ensure that case folding of subtags does not produce this value, which is illegal in language tags. For example, if one were to uppercase the region subtag 'in' using Turkish locale rules, the sequence U+0130 U+004E would result instead of the expected 'IN'. Note: if the field 'Deprecated' appears in a registry record without an accompanying 'Canonical' 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 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. Phillips & Davis Expires November 20, 2005 [Page 41] Internet-Draft langtags-registry May 2005 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 be useful. For example, the region subtags 'AA', 'ZZ' and in the ranges 'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166 private use codes) may be used to form a language tag. A tag such as "zh-Hans-XQ" conveys a great deal of public, interchangeable information about the language material (that it is Chinese in the simplified Chinese script and is suitable for some geographic region 'XQ'). While the precise geographic region is not known outside of private agreement, the tag conveys far more information than an opaque tag such as "x-someLang", which contains no information about the language subtag or script subtag outside of the private agreement. However, in some cases content tagged with private use subtags may interact with other systems in a different and possibly unsuitable manner compared to tags that use opaque, privately defined subtags, so the choice of the best approach may depend on the particular domain in question. Phillips & Davis Expires November 20, 2005 [Page 42] Internet-Draft langtags-registry May 2005 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 . 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 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 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 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. Phillips & Davis Expires November 20, 2005 [Page 43] Internet-Draft langtags-registry May 2005 6. Security Considerations The only security issue that has been raised with language tags since the publication of RFC 1766 [21], which stated that "Security issues are believed to be irrelevant to this memo", is a concern with language identifiers used in content negotiation - that they may be used to infer the nationality of the sender, and thus identify potential targets for surveillance. This is a special case of the general problem that anything 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] for best current practice guidance on security threats and defenses). Although the specification of valid subtags for an extension MUST be available over the Internet, implementations SHOULD NOT mechanically depend on it being always accessible, to prevent denial-of-service attacks. Phillips & Davis Expires November 20, 2005 [Page 44] Internet-Draft langtags-registry May 2005 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 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. Phillips & Davis Expires November 20, 2005 [Page 45] Internet-Draft langtags-registry May 2005 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]) 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 Phillips & Davis Expires November 20, 2005 [Page 46] Internet-Draft langtags-registry May 2005 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. Phillips & Davis Expires November 20, 2005 [Page 47] Internet-Draft langtags-registry May 2005 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-01 and this version are: o Minor updates to the changes section (the text just above) to reflect various updates in the WG drafts (A.Phillips) o Minor change to the section on the extensions registry (because there can be 35, not 25, entries maximum. (D.Ewell) o Changed "SHOULD NOT permit a subtag to be divided" to MUST NOT. (#944) (R.Presuhn) o Added text to Section 3.1 and Section 4.1 describing the rationale for Suppress-Script. Both sentences are slight rewordings of this text suggested in the email thread: "This 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." (#954) (F.Ellermann, A.Phillips) o Added text about case folding during canonicalization. This also includes rules in Section 3.2 for casing of registry entries, as well the insertion of the text permitting case normalization in Section 4.3 and the warning about locale-specific casing operations in the same section. (#985) (F.Ellermann, J.Cowan, A.Phillips) o Fixed the reference to Canonical-Value in Section 4.3. (A.Phillips) Phillips & Davis Expires November 20, 2005 [Page 48] Internet-Draft langtags-registry May 2005 o In Section 3.4, changed the reference from the subtag 'nv' to the tag "nv" to be consistent with the wording in Section 3.1. (part of #954) (D.Ewell) o Added missing word 'that' in Section 3.6 (A.Phillips) Phillips & Davis Expires November 20, 2005 [Page 49] Internet-Draft langtags-registry May 2005 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, Phillips & Davis Expires November 20, 2005 [Page 50] Internet-Draft langtags-registry May 2005 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] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [15] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. 9.2 Informative References [16] ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance", March 2000, . [17] Raymond, E., "The Art of Unix Programming", 2003. [18] Bray (et al), T., "Extensible Markup Language (XML) 1.0", 02 2004. [19] Biron, P., Ed. and A. Malhotra, Ed., "XML Schema Part 2: Datatypes Second Edition", 10 2004, < http://www.w3.org/TR/xmlschema-2/>. [20] 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] Alvestrand, H., "Tags for the Identification of Languages", RFC 1766, March 1995. [22] Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations", RFC 2231, November 1997. [23] Alvestrand, H., "Tags for the Identification of Languages", BCP 47, RFC 3066, January 2001. Phillips & Davis Expires November 20, 2005 [Page 51] Internet-Draft langtags-registry May 2005 Authors' Addresses Addison Phillips (editor) Quest Software Email: addison.phillips@quest.com Mark Davis (editor) IBM Email: mark.davis@us.ibm.com Phillips & Davis Expires November 20, 2005 [Page 52] Internet-Draft langtags-registry May 2005 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. Phillips & Davis Expires November 20, 2005 [Page 53] Internet-Draft langtags-registry May 2005 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 because subtag 'sl' has a Suppress-Script value of 'Latn') Language-Region: Phillips & Davis Expires November 20, 2005 [Page 54] Internet-Draft langtags-registry May 2005 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 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 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) Phillips & Davis Expires November 20, 2005 [Page 55] Internet-Draft langtags-registry May 2005 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) Phillips & Davis Expires November 20, 2005 [Page 56] Internet-Draft langtags-registry May 2005 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 Phillips & Davis Expires November 20, 2005 [Page 57] Internet-Draft langtags-registry May 2005 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: Åland 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 Phillips & Davis Expires November 20, 2005 [Page 58] Internet-Draft langtags-registry May 2005 orthography Added: 2004-09-09 Recommended-Prefix: de Comment: %% Type: variant Subtag: 1996 Description: German orthography of 1996 Added: 2004-09-09 Recommended-Prefix: de %% Type: variant Subtag: boont Description: Boontling Added: 2003-02-14 Recommended-Prefix: en %% Type: variant Subtag: gaulish Description: Gaulish Added: 2001-05-25 Recommended-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 Phillips & Davis Expires November 20, 2005 [Page 59] Internet-Draft langtags-registry May 2005 Added: 2003-05-30 %% Type: redundant Tag: az-Cyrl Description: Azerbaijani in Cyrillic script Added: 2003-05-30 %% Figure 7: Example of the Registry Format Phillips & Davis Expires November 20, 2005 [Page 60] Internet-Draft langtags-registry May 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Phillips & Davis Expires November 20, 2005 [Page 61]