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Copyright © The IETF Trust (2007).
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.
1.
Introduction
2.
The Language Tag
2.1.
Syntax
2.2.
Language Subtag Sources and Interpretation
2.2.1.
Primary Language Subtag
2.2.2.
Extended Language Subtags
2.2.3.
Script Subtag
2.2.4.
Region Subtag
2.2.5.
Variant Subtags
2.2.6.
Extension Subtags
2.2.7.
Private Use Subtags
2.2.8.
Grandfathered Registrations
2.2.9.
Classes of Conformance
3.
Registry Format and Maintenance
3.1.
Format of the IANA Language Subtag Registry
3.1.1.
File Format
3.1.2.
Record Definitions
3.1.3.
Subtag and Tag Fields
3.1.4.
Description Field
3.1.5.
Deprecated Field
3.1.6.
Preferred-Value Field
3.1.7.
Prefix Field
3.1.8.
Comments Field
3.1.9.
Suppress-Script Field
3.2.
Language Subtag Reviewer
3.3.
Maintenance of the Registry
3.4.
Stability of IANA Registry Entries
3.5.
Registration Procedure for Subtags
3.6.
Possibilities for Registration
3.7.
Extensions and Extensions Registry
3.8.
Update of the Language Subtag Registry
4.
Formation and Processing of Language Tags
4.1.
Choice of Language Tag
4.2.
Meaning of the Language Tag
4.3.
Length Considerations
4.3.1.
Working with Limited Buffer Sizes
4.3.2.
Truncation of Language Tags
4.4.
Canonicalization of Language Tags
4.5.
Considerations for Private Use Subtags
5.
IANA Considerations
5.1.
Language Subtag Registry
5.2.
Extensions Registry
6.
Security Considerations
7.
Character Set Considerations
8.
Changes from RFC 4646
9.
References
9.1.
Normative References
9.2.
Informative References
Appendix A.
Acknowledgements
Appendix B.
Examples of Language Tags (Informative)
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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Human beings on our planet have, past and present, used a number of languages. There are many reasons why one would want to identify the language used when presenting or requesting information.
A user's language preferences often need to be identified so that appropriate processing can be applied. For example, the user's language preferences in a Web browser can be used to select Web pages appropriately. Language preferences can also be used to select among tools (such as dictionaries) to assist in the processing or understanding of content in different languages.
In addition, knowledge about the particular language used by some piece of information content might be useful or even required by some types of processing; for example, spell-checking, computer-synthesized speech, Braille transcription, or high-quality print renderings.
One means of indicating the language used is by labeling the information content with an identifier or "tag". These tags can be used to specify user preferences when selecting information content, or for labeling additional attributes of content and associated resources.
Tags can also be used to indicate additional language attributes of content. For example, indicating specific information about the dialect, writing system, or orthography used in a document or resource may enable the user to obtain information in a form that they can understand, or it can be important in processing or rendering the given content into an appropriate form or style.
This document specifies a particular identifier mechanism (the language tag) and a registration function for values to be used to form tags. It also defines a mechanism for private use values and future extension.
This document replaces [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.), which replaced [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.) and its predecessor [RFC1766] (Alvestrand, H., “Tags for the Identification of Languages,” March 1995.). For a list of changes in this document, see Section 8 (Changes from RFC 4646).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
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Language tags are used to help identify languages, whether spoken, written, signed, or otherwise signaled, for the purpose of communication. This includes constructed and artificial languages, but excludes languages not intended primarily for human communication, such as programming languages.
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The language tag is composed of one or more parts, known as "subtags". Each subtag consists of a sequence of alphanumeric characters. Subtags are distinguished and separated from one another by a hyphen ("-", ABNF [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.) %x2D). A language tag consists of a "primary language" subtag and a (possibly empty) series of subsequent subtags, each of which refines or narrows the range of languages identified by the overall tag.
Usually, each type of subtag is distinguished by length, position in the tag, and content: subtags can be recognized solely by these features. The only exception to this is a fixed list of grandfathered tags registered under RFC 3066 (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.) [RFC3066]. This makes it possible to construct a parser that can extract and assign some semantic information to the subtags, even if the specific subtag values are not recognized. Thus, a parser need not have an up-to-date copy (or any copy at all) of the subtag registry to perform most searching and matching operations.
The syntax of the language tag in ABNF [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.) is:
Language-Tag = langtag
/ privateuse ; private use tag
/ irregular ; tags grandfathered by rule
langtag = (language
["-" script]
["-" region]
*("-" variant)
*("-" extension)
["-" privateuse])
language = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code
/ 4ALPHA ; reserved for future use
/ 5*8ALPHA ; registered language subtag
extlang = *3("-" 3ALPHA) ; specific ISO 639-3 codes
script = 4ALPHA ; ISO 15924 code
region = 2ALPHA ; ISO 3166 code
/ 3DIGIT ; UN M.49 code
variant = 5*8alphanum ; registered variants
/ (DIGIT 3alphanum)
extension = singleton 1*("-" (2*8alphanum))
singleton = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT
; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9"
; Single alphanumerics
; "x" is reserved for private use
privateuse = "x" 1*("-" (1*8alphanum))
irregular = "en-GB-oed" / "i-ami" / "i-bnn" / "i-default"
/ "i-enochian" / "i-hak" / "i-klingon" / "i-lux"
/ "i-mingo" / "i-navajo" / "i-pwn" / "i-tao"
/ "i-tay" / "i-tsu" / "sgn-BE-fr" / "sgn-BE-nl"
/ "sgn-CH-de"
alphanum = (ALPHA / DIGIT) ; letters and numbers
| Figure 1: Language Tag ABNF |
All subtags have a maximum length of eight characters and whitespace is not permitted in a language tag. There is a subtlety in the ABNF production 'variant': variants starting with a digit MAY be four characters long, while those starting with a letter MUST be at least five characters long. For examples of language tags, see Appendix B (Examples of Language Tags (Informative)).
Note Well: the ABNF syntax does not distinguish between upper and lowercase. The appearance of upper and lowercase letters in the varous ABNF productions above do not affect how implementations interpret tags. That is, the tag "I-AMI" matches the item "i-ami" in the 'irregular' production. At all times, the tags and their subtags, including private use and extensions, are to be treated as case insensitive: there exist conventions for the capitalization of some of the subtags, but these MUST NOT be taken to carry meaning.
For example:
However, in the tags defined by this document, the uppercase US-ASCII letters in the range 'A' through 'Z' are considered equivalent and mapped directly to their US-ASCII lowercase equivalents in the range 'a' through 'z'. Thus, the tag "mn-Cyrl-MN" is not distinct from "MN-cYRL-mn" or "mN-cYrL-Mn" (or any other combination), and each of these variations conveys the same meaning: Mongolian written in the Cyrillic script as used in Mongolia.
Although case distinctions do not carry meaning in language tags, consistent formatting and presentation of the tags will aid users. The format of the tags and subtags in the registry is RECOMMENDED. In this format, all non-initial two-letter subtags are uppercase, all non-initial four-letter subtags are titlecase, and all other subtags are lowercase.
Note that although [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.) refers to octets, the language tags described in this document are sequences of characters from the US-ASCII [ISO646] (International Organization for Standardization, “ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.,” 1991.) repertoire. Language tags MAY be used in documents and applications that use other encodings, so long as these encompass the US-ASCII repertoire. An example of this would be an XML document that uses the UTF-16LE [RFC2781] (Hoffman, P. and F. Yergeau, “UTF-16, an encoding of ISO 10646,” February 2000.) encoding of [Unicode] (Unicode Consortium, “The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0),” January 2007.).
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The namespace of language tags and their subtags is administered by the Internet Assigned Numbers Authority (IANA) [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) according to the rules in Section 5 (IANA Considerations) of this document. The Language Subtag Registry maintained by IANA is the source for valid subtags: other standards referenced in this section provide the source material for that registry.
Terminology used in this document:
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 (Grandfathered Registrations).
Language tags are designed so that each subtag type has unique length and content restrictions. These make identification of the subtag's type possible, even if the content of the subtag itself is unrecognized. This allows tags to be parsed and processed without reference to the latest version of the underlying standards or the IANA registry and makes the associated exception handling when parsing tags simpler.
Subtags in the IANA registry that do not come from an underlying standard can only appear in specific positions in a tag. Specifically, they can only occur as primary language subtags or as variant subtags.
Note that sequences of private use and extension subtags MUST occur at the end of the sequence of subtags and MUST NOT be interspersed with subtags defined elsewhere in this document.
Single-letter and single-digit subtags are reserved for current or future use. These include the following current uses:
The single-letter subtag 'i' is used by some grandfathered tags, such as "i-default", where it always appears in the first position and cannot be confused with an extension.
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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:
Note: For languages that have both an ISO 639-1 two-character code and a three character code assigned by either ISO 639-2 or ISO 639-3, only the ISO 639-1 two-character code is defined in the IANA registry.
Note: For languages that have no ISO 639-1 two-character code and for which the ISO 639-2/T (Terminology) code and the ISO 639-2/B (Bibliographic) codes differ, only the Terminology code is defined in the IANA registry. At the time this document was created, all languages that had both kinds of three-character code were also assigned a two-character code; it is expected that future assignments of this nature will not occur.
Note: To avoid problems with versioning and subtag choice as experienced during the transition between RFC 1766 and RFC 3066, as well as the canonical nature of subtags defined by this document, the ISO 639 Registration Authority Joint Advisory Committee (ISO 639/RA-JAC) has included the following statement in [iso639.prin] (ISO 639 Joint Advisory Committee, “ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance,” March 2000.):
"A language code already in ISO 639-2 at the point of freezing ISO 639-1 shall not later be added to ISO 639-1. This is to ensure consistency in usage over time, since users are directed in Internet applications to employ the alpha-3 code when an alpha-2 code for that language is not available."
In order to avoid instability in the canonical form of tags, if a two-character code is added to ISO 639-1 for a language for which a three-character code was already included in either ISO 639-2 or ISO 639-3, the two-character code MUST NOT be registered. See Section 3.4 (Stability of IANA Registry Entries).
For example, if some content were tagged with 'haw' (Hawaiian), which currently has no two-character code, the tag would not be invalidated if ISO 639-1 were to assign a two-character code to the Hawaiian language at a later date.
Note: An example of independent primary language subtag registration might include: one of the grandfathered IANA registrations is "i-enochian". The subtag 'enochian' could be registered in the IANA registry as a primary language subtag (assuming that ISO 639 does not register this language first), making tags such as "enochian-AQ" and "enochian-Latn" valid.
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Extended language subtags are used to identify languages that are encompassed by a "macrolanguage". ISO 639-3 defines certain languages to be "macrolanguages"; that is, they are groups of very closely related languages which are treated as a single language in certain contexts. In order to improve matching behavior and tagging consistency, each language encompassed by a ISO 639-3 macrolanguage is represented in the IANA registry using an extended language subtag, provided that it is not already represented using a language subtag. The following rules apply to the extended language subtags:
Extended language subtag records MUST include exactly one 'Prefix' field indicating an appropriate subtag or sequence of subtags for that extended language subtag.
For example, the 'gan' and 'cmn' subtags represent the languages Gan Chinese and Mandarin Chinese. Each is encompassed by the macrolanguage 'zh' (Chinese). Therefore, they both have the prefix "zh" in their registry records. Consequently, Gan Chinese is represented as "zh-gan" and Mandarin Chinese as "zh-cmn". The language subtag 'zh' can still be used without an extended language subtag to label a resource as some unspecified variety of Chinese (which in practice will usually be Mandarin, the dominant variety of Chinese, but might also be some other variety).
Now suppose that, in the future, the ISO 639-3 Registration Authority were to decide that Gan Chinese is actually two different closely related languages: it might reclassify 'gan' as a macrolanguage and introduce two new code elements. In that case, these code elements would be added to the IANA registry as extended language subtags with prefixes of "zh-gan". No change would be made to the registry record for 'gan'.
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Script subtags are used to indicate the script or writing system variations that distinguish the written forms of a language or its dialects. The following rules apply to the script subtags:
Example: "sr-Latn" represents Serbian written using the Latin script.
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Region subtags are used to indicate linguistic variations associated with or appropriate to a specific country, territory, or region. Typically, a region subtag is used to indicate regional dialects or usage, or region-specific spelling conventions. A region subtag can also be used to indicate that content is expressed in a way that is appropriate for use throughout a region, for instance, Spanish content tailored to be useful throughout Latin America.
The following rules apply to the region subtags:
- A.
- UN numeric codes assigned to 'macro-geographical (continental)' or sub-regions MUST be registered in the registry. These codes are not associated with an assigned ISO 3166 alpha-2 code and represent supra-national areas, usually covering more than one nation, state, province, or territory.
- B.
- UN numeric codes for 'economic groupings' or 'other groupings' MUST NOT be registered in the IANA registry and MUST NOT be used to form language tags.
- C.
- UN numeric codes for countries or areas with ambiguous ISO 3166 alpha-2 codes, when entered into the registry, MUST be defined according to the rules in Section 3.4 (Stability of IANA Registry Entries) and MUST be used to form language tags that represent the country or region for which they are defined.
- D.
- UN numeric codes for countries or areas for which there is an associated ISO 3166 alpha-2 code in the registry MUST NOT be entered into the registry and MUST NOT be used to form language tags. Note that the ISO 3166-based subtag in the registry MUST actually be associated with the UN M.49 code in question.
- E.
- UN numeric codes and ISO 3166 alpha-2 codes for countries or areas listed as eligible for registration in [RFC4645] (Ewell, D., Ed., “Initial Language Subtag Registry,” September 2006.) but not presently registered MAY be entered into the IANA registry via the process described in Section 3.5 (Registration Procedure for Subtags). Once registered, these codes MAY be used to form language tags.
- F.
- All other UN numeric codes for countries or areas that do not have an associated ISO 3166 alpha-2 code MUST NOT be entered into the registry and MUST NOT be used to form language tags. For more information about these codes, see Section 3.4 (Stability of IANA Registry Entries).
"de-CH" represents German ('de') as used in Switzerland ('CH').
"sr-Latn-RS" represents Serbian ('sr') written using Latin script ('Latn') as used in Serbia ('RS').
"es-419" represents Spanish ('es') appropriate to the UN-defined Latin America and Caribbean region ('419').
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Variant subtags are used to indicate additional, well-recognized variations that define a language or its dialects that are not covered by other available subtags. The following rules apply to the variant subtags:
Variant subtag records in the language subtag registry MAY include one or more 'Prefix' fields, which indicate the language tag or tags that would make a suitable prefix (with other subtags, as appropriate) in forming a language tag with the variant. For example, the subtag 'nedis' has a Prefix of "sl", making it suitable to form language tags such as "sl-nedis" and "sl-IT-nedis", but not suitable for use in a tag such as "zh-nedis" or "it-IT-nedis".
"sl-nedis" represents the Natisone or Nadiza dialect of Slovenian.
"de-CH-1996" represents German as used in Switzerland and as written using the spelling reform beginning in the year 1996 C.E.
Most variants that share a prefix are mutually exclusive. For example, the German orthographic variations '1996' and '1901' SHOULD NOT be used in the same tag, as they represent the dates of different spelling reforms. A variant that can meaningfully be used in combination with another variant SHOULD include a 'Prefix' field in its registry record that lists that other variant. For example, if another German variant 'example' were created that made sense to use with '1996', then 'example' should include two Prefix fields: "de" and "de-1996".
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Extensions provide a mechanism for extending language tags for use in various applications. See Section 3.7 (Extensions and Extensions Registry). The following rules apply to extensions:
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"
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Private use subtags are used to indicate distinctions in language important in a given context by private agreement. The following rules apply to private use subtags:
For example: Users who wished to utilize codes from the Ethnologue publication of SIL International for language identification might agree to exchange tags such as "az-Arab-x-AZE-derbend". This example contains two private use subtags. The first is 'AZE' and the second is 'derbend'.
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Prior to RFC 4646, whole language tags were registered according to the rules in RFC 1766 and/or RFC 3066. These registered tags maintain their validity. Of those tags, those that were made obsolete or redundant by the advent of RFC 4646, by this document, or by subsequent registration of subtags are maintained in the registry in records as "redundant" records. Those tags that do not match the 'langtag' production in the ABNF in this document or that contain subtags that do not individually appear in the registry are maintained in the registry in records of the "grandfathered" type.
Grandfathered tags contain one or more subtags that are not defined in the Language Subtag Registry (see Section 3 (Registry Format and Maintenance)). Redundant tags consist entirely of subtags defined above and whose independent registration was superseded by [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.). For more information see Section 3.8 (Update of the Language Subtag Registry).
Some grandfathered tags are "regular" in that they match the 'langtag' production in Figure 1 (Language Tag ABNF). In some cases, these tags could become redundant if their (current unregistered) subtags were to be registered (as variants, for example). In other cases, although the subtags match the language tag pattern, the meaning assigned to the various subtags is prohibited by rules elsewhere in this document. Those tags can never become redundant.
The remaining grandfathered tags are "irregular" and do not match the 'langtag' production. These are listed in the 'irregular' production in Figure 1 (Language Tag ABNF). These grandfathered tags can never become redundant. Many of these tags have been superseded by other registrations: their record contains a Preferred-Value field that really ought to be used to form language tags representing that value.
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Implementations sometimes need to describe their capabilities with regard to the rules and practices described in this document. Tags can be checked or verified in a number of ways, but two particular classes of tag conformance are formally defined here.
A tag is considered "well-formed" if it conforms to the ABNF (Syntax). Note that irregular grandfathered tags are now listed in the 'irregular' production.
A tag is considered "valid" if it well-formed and it also satisfies these conditions:
Note that a tag's validity depends on the date of the registry used to validate the tag. A more-recent copy of the registry might contain a subtag that an older version does not.
A tag is considered "valid" for a given extension (Extensions and Extensions Registry) (as of a particular version, revision, and date) if it meets the criteria for "valid" above and also satisfies this condition:
Each subtag used in the extension part of the tag is valid according to the extension.
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This section defines the Language Subtag Registry and the maintenance and update procedures associated with it, as well as a registry for extensions to language tags (Section 3.7 (Extensions and Extensions Registry)).
The Language Subtag Registry contains a comprehensive list of all of the subtags valid in language tags. This allows implementers a straightforward and reliable way to validate language tags. The Language Subtag Registry will be maintained so that, except for extension subtags, it is possible to validate all of the subtags that appear in a language tag under the provisions of this document or its revisions or successors. In addition, the meaning of the various subtags will be unambiguous and stable over time. (The meaning of private use subtags, of course, is not defined by the IANA registry.)
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The IANA Language Subtag Registry ("the registry") consists of a text file that is machine readable in the format described in this section, plus copies of the registration forms approved in accordance with the process described in Section 3.5 (Registration Procedure for Subtags). The existing registration forms for grandfathered and redundant tags taken from RFC 3066 will be maintained as part of the obsolete RFC 3066 registry. The remaining set of initial subtags will not have registration forms created for them.
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The registry is in the text format described below. This format was based on the record-jar format described in [record‑jar] (Raymond, E., “The Art of Unix Programming,” 2003.).
Each line of text is limited to 72 characters, including all whitespace. Records are separated by lines containing only the sequence "%%" (%x25.25).
Each field can be viewed as a single, logical line of ASCII characters, comprising a field-name and a field-body separated by a COLON character (%x3A). For convenience, the field-body portion of this conceptual entity can be split into a multiple-line representation; this is called "folding". The format of the registry is described by the following ABNF (per [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.)):
registry = record *("%%" CRLF record)
record = 1*( field-name *SP ":" *SP field-body CRLF )
field-name = (ALPHA / DIGIT) [*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)]
field-body = *(ASCCHAR/LWSP)
ASCCHAR = %x21-25 / %x27-7E / UNICHAR ; Note: AMPERSAND is %x26
UNICHAR = "&#x" 2*6HEXDIG ";"
| Figure 2: Registry Format ABNF |
The sequence '..' (%x2E.2E) in a field-body denotes a range of values. Such a range represents all subtags of the same length that are in alphabetic or numeric order within that range, including the values explicitly mentioned. For example 'a..c' denotes the values 'a', 'b', and 'c' and '11..13' denotes the values '11', '12', and '13'.
Characters from outside the US-ASCII (International Organization for Standardization, “ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.,” 1991.) [ISO646] repertoire, as well as the AMPERSAND character ("&", %x26) when it occurs in a field-body, are represented by a "Numeric Character Reference" using hexadecimal notation in the style used by [XML10] (Bray (et al), T., “Extensible Markup Language (XML) 1.0,” 02 2004.) (see http://www.w3.org/TR/REC-xml/#dt-charref). This consists of the sequence "&#x" (%x26.23.78) followed by a hexadecimal representation of the character's code point in [ISO10646] (International Organization for Standardization, “ISO/IEC 10646:2003. Information technology -- Universal Multiple-Octet Coded Character Set (UCS),” 2003.) 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 [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.). For example: "2004-06-28" represents June 28, 2004, in the Gregorian calendar.
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There are three types of records in the registry: "File-Date", "Subtag", and "Tag" records.
The first record in the registry is a "File-Date" record. This record contains the single field whose field-name is "File-Date" (see Figure 2 (Registry Format ABNF)). The field-body of this record contains the last modification date of this copy of the registry, making it possible to compare different versions of the registry. The registry on the IANA website is the most current. Versions with an older date than that one are not up-to-date.
File-Date: 2004-06-28 %%
| Figure 3: Example of the File-Date Record |
Subsequent records represent either subtags or tags in the registry. "Subtag" records contain a field with a field-name of "Subtag", while, unsurprisingly, "Tag" records contain a field with a field-name of "Tag". Each of the fields in each record MUST occur no more than once, unless otherwise noted below. Each record MUST contain the following fields:
Each record MAY also contain the following fields:
Future versions of this document might add additional fields to the registry, so implementations SHOULD ignore fields found in the registry that are not defined in this document.
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The 'Subtag' field MUST use lowercase letters to form the subtag, with two exceptions. Subtags whose 'Type' field is 'script' (in other words, subtags defined by ISO 15924) MUST use titlecase. Subtags whose 'Type' field is 'region' (in other words, subtags defined by ISO 3166) MUST use uppercase. These exceptions mirror the use of case in the underlying standards.
Each subtag in the tags contained in a 'Tag' field MUST be formatted using the rules in the preceeding paragraph. That is, all subtags are lowercase except for subtags that represent script or region codes.
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The field 'Description' contains a description of the tag or subtag in the record. The 'Description' field MAY appear more than once per record, that is, there can be multiple descriptions for a given record. At least one of the 'Description' fields MUST be written or transcribed into the Latin script; additional 'Description' fields MAY also include a description in a non-Latin script. Each 'Description' field MUST be unique, both within the record in which it appears and for the collection of records of the same type. Moreover, formatting variations of the same description MUST NOT occur in that specific record or in any other record of the same type. For example, while the ISO 639-1 code 'fy' contains both the descriptions "Western Frisian" and "Frisian, Western", only one of these descriptions appears in the registry.
The 'Description' field is used for identification purposes and SHOULD NOT be taken to represent the actual native name of the language or variation or to be in any particular language.
For records taken from a source standard (such as ISO 639 or ISO 3166), the 'Description' value(s) SHOULD also be taken from the source standard. Multiple descriptions in the source standard MUST be split into separate 'Description' fields. The source standard's descriptions MAY be edited, either prior to insertion or via the registration process. For fields of type 'language' or 'extlang', the first 'Description' field appearing in the Registry corresponds to the Reference Name assigned by ISO 639-3. This helps facilitate cross-referencing between ISO 639 and the registry.
When creating or updating a record due to the action of one of the source standards, the Language Subtag Reviewer SHOULD remove duplicate or redundant descriptions and MAY edit descriptions to correct irregularities in formatting (such as misspellings, inappropriate apostrophes or other punctuation, or excessive or missing spaces) prior to submitting the proposed record to the ietf-languages list.
Note: Descriptions in registry entries that correspond to ISO 639, ISO 15924, ISO 3166, or UN M.49 codes are intended only to indicate the meaning of that identifier as defined in the source standard at the time it was added to the registry. The description does not replace the content of the source standard itself. The descriptions are not intended to be the English localized names for the subtags. Localization or translation of language tag and subtag descriptions is out of scope of this document.
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The field 'Deprecated' MAY be added to any record via the maintenance process described in Section 3.3 (Maintenance of the Registry) or via the registration process described in Section 3.5 (Registration Procedure for Subtags). Usually, the addition of a 'Deprecated' field is due to the action of one of the standards bodies, such as ISO 3166, withdrawing a code. In some historical cases, it might not have been possible to reconstruct the original deprecation date. For these cases, an approximate date appears in the registry. Although valid in language tags, subtags and tags with a 'Deprecated' field are deprecated and validating processors SHOULD NOT generate these subtags. Note that a record that contains a 'Deprecated' field and no corresponding 'Preferred-Value' field has no replacement mapping.
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The field 'Preferred-Value' contains a mapping between the record in which it appears and another tag or subtag. The value in this field is strongly RECOMMENDED as the best choice to represent the value of this record when selecting a language tag. These values form three groups:
Records that contain a 'Preferred-Value' field MUST also have a 'Deprecated' field. This field contains a date of deprecation. Thus, a language tag processor can use the registry to construct the valid, non-deprecated set of subtags for a given date. In addition, for any given tag, a processor can construct the set of valid language tags that correspond to that tag for all dates up to the date of the registry. The ability to do these mappings MAY be beneficial to applications that are matching, selecting, for filtering content based on its language tags.
Note that 'Preferred-Value' mappings in records of type 'region' sometimes do not represent exactly the same meaning as the original value. There are many reasons for a country code to be changed, and the effect this has on the formation of language tags will depend on the nature of the change in question.
In particular, the 'Preferred-Value' field does not imply retagging content that uses the affected subtag.
The field 'Preferred-Value' MUST NOT be modified once created in the registry. The field MAY be added to records according to the rules in Section 3.3 (Maintenance of the Registry).
The 'Preferred-Value' field in records of type "grandfathered" and "redundant" contains whole language tags that are strongly RECOMMENDED for use in place of the record's value. In many cases, the mappings were created by deprecation of the tags during the period before this document was adopted. For example, the tag "no-nyn" was deprecated in favor of the ISO 639-1-defined language code 'nn'.
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The field of type 'Prefix' MUST NOT be removed from any record. The field-body for this type of field MAY be modified, but only if the modification broadens the meaning of the subtag. That is, the field-body can be replaced only by a prefix a prefix of itself. For example, the Prefix "be-Latn" (Belarusian, Latin script) could be replaced by the Prefix "be" (Belarusian) but not by the Prefix "ru-Latn" (Russian, Latin script).
The field-body of the 'Prefix' field consists of a language tag whose subtags are appropriate to use with this subtag. For example, the variant subtag '1996' has a 'Prefix' field of "de". This means that tags starting with the sequence "de-" are appropriate with this subtag, so "de-Latg-1996" and "de-CH-1996" are both acceptable, while the tag "fr-1996" is an inappropriate choice.
Records of type 'variant' MAY have more than one field of type 'Prefix'. Additional fields of this type MAY be added to a 'variant' record via the registration process.
The field-body of the 'Prefix' field MUST NOT conflict with any 'Prefix' already registered for a given record. Such a conflict would occur when when no valid tag could be constructed that would contain the prefix, such as when when two subtags each have a 'Prefix' that contains the other subtag. For example, suppose that the subtag 'avariant' has the prefix "es-bvariant". Then the subtag 'bvariant' cannot given the prefix 'avariant', for that would require a tag of the form "es-avariant-bvariant-avariant", which would not be valid.
Records of type 'extlang' MUST have exactly one 'Prefix' field.
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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.
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The field 'Suppress-Script' MUST only appear in records whose 'Type' field-body is 'language'. This field MUST NOT appear more than one time in a record. This field indicates a script used to write the overwhelming majority of documents for the given language and that 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".
Many language subtag records do not have a Suppress-Script field. The lack of a Suppress-Script might indicate that the language is customarily written in more than one script or that the language is not customarily written at all. It might also mean that sufficient information was not available when the record was created and thus remains a candidate for future registration.
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The Language Subtag Reviewer moderates the ietf-languages mailing list, responds to requests for registration, and performs the other registry maintenance duties described in Section 3.3 (Maintenance of the Registry). Only the Language Subtag Reviewer is permitted to request IANA to change, update, or add records to the Language Subtag Registry. The Language Subtag Reviewer MAY delegate list moderation and other clerical duties as needed.
The Language Subtag Reviewer is appointed by the IESG for an indefinite term, subject to removal or replacement at the IESG's discretion. The IESG will solicit nominees for the position (initially or upon a vacancy) and seek to ascertain the candidates' qualifications.
The subsequent performance or decisions of the Language Subtag Reviewer MAY be appealed to the IESG under the same rules as other IETF decisions (see [RFC2026] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.)). The IESG can reverse or overturn the decision of the Language Subtag Reviewer, provide guidance, or take other appropriate actions.
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Maintenance of the registry requires that as codes are assigned or withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language Subtag Reviewer MUST evaluate each change, determine whether it conflicts with existing registry entries, and submit the information to IANA for inclusion in the registry. If a change takes place and the Language Subtag Reviewer does not do this in a timely manner, then any interested party MAY use the procedure in Section 3.5 (Registration Procedure for Subtags) to register the appropriate update.
Note: The redundant and grandfathered entries together are the complete list of tags registered under [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.). 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 (Language Subtag Sources and Interpretation). The grandfathered entries include those that can never be legal under those same provisions plus those tags that contain subtags not yet registered or, perhaps, inappropriate for registration.
The set of redundant and grandfathered tags is permanent and stable: new entries in this section MUST NOT be added and existing entries MUST NOT be removed. Records of type 'grandfathered' MAY have their type converted to 'redundant'; see item 12 in Section 3.6 (Possibilities for Registration) for more information. The decision-making process about which tags were initially grandfathered and which were made redundant is described in [RFC4645] (Ewell, D., Ed., “Initial Language Subtag Registry,” September 2006.).
RFC 3066 tags that were deprecated prior to the adoption of [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.) 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 (Choice of Language Tag) or submit an appropriate alternate subtag as described in that section. When either a change or addition to the registry is needed, the Language Subtag Reviewer MUST prepare the complete record, including all fields, and forward it to IANA for insertion into the registry. Each record being modified or inserted MUST be forwarded in a separate message.
If a record represents a new subtag that does not currently exist in the registry, then the message's subject line MUST include the word "INSERT". If the record represents a change to an existing subtag, then the subject line of the message MUST include the word "MODIFY". The message MUST contain both the record for the subtag being inserted or modified and the new File-Date record. Here is an example of what the body of the message might contain:
LANGUAGE SUBTAG MODIFICATION File-Date: 2005-01-02 %% Type: variant Subtag: nedis Description: Natisone dialect Description: Nadiza dialect Added: 2003-10-09 Prefix: sl Comments: This is a comment shown as an example. %%
| Figure 4: Example of a Language Subtag Modification Form |
Whenever an entry is created or modified in the registry, the 'File-Date' record at the start of the registry is updated to reflect the most recent modification date in the [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.) "full-date" format.
Before forwarding a new registration to IANA, the Language Subtag Reviewer MUST ensure that values in the 'Subtag' field match case according to the description in Section 3.1 (Format of the IANA Language Subtag Registry).
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The stability of entries and their meaning in the registry is critical to the long-term stability of language tags. The rules in this section guarantee that a specific language tag's meaning is stable over time and will not change.
These rules specifically deal with how changes to codes (including withdrawal and deprecation of codes) maintained by ISO 639, ISO 15924, ISO 3166, and UN M.49 are reflected in the IANA Language Subtag Registry. Assignments to the IANA Language Subtag Registry MUST follow the following stability rules:
- Example
- The region code 'TL' was assigned to the country 'Timor-Leste', replacing the code 'TP' (which was assigned to 'East Timor' when it was under administration by Portugal). The subtag 'TP' remains valid in language tags, but its record contains the a 'Preferred-Value' of 'TL' and its field 'Deprecated' contains the date the new code was assigned ('2004-07-06').
- A.
- For ISO 639 codes, if the newly assigned code's meaning is not represented by a subtag in the IANA registry, the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered language subtag as an alternate value for the new code. The form of the registered language subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on language subtags in this document.
- B.
- For all subtags whose meaning is derived from an external standard (that is, by ISO 639, ISO 15924, ISO 3166, or UN M.49), if a new meaning is assigned to an existing code and the new meaning broadens the meaning of that code, then the meaning for the associated subtag MAY be changed to match. The meaning of a subtag MUST NOT be narrowed, however, as this can result in an unknown proportion of the existing uses of a subtag becoming invalid. Note: ISO 639 maintenance agency/registration authority (MA/RA) has adopted a similar stability policy.
- C.
- For ISO 15924 codes, if the newly assigned code's meaning is not represented by a subtag in the IANA registry, the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on variant subtags in this document.
- D.
- For ISO 3166 codes, if the newly assigned code's meaning is associated with the same UN M.49 code as another 'region' subtag, then the existing region subtag remains as the preferred value for that region and no new entry is created. A comment MAY be added to the existing region subtag indicating the relationship to the new ISO 3166 code.
- E.
- For ISO 3166 codes, if the newly assigned code's meaning is associated with a UN M.49 code that is not represented by an existing region subtag, then the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering the appropriate UN M.49 country code as an entry in the IANA registry.
- F.
- For ISO 3166 codes, if there is no associated UN numeric code, then the Language Subtag Reviewer SHALL petition the UN to create one. If there is no response from the UN within ninety days of the request being sent, the Language Subtag Reviewer SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on variant subtags in this document. This situation is very unlikely to ever occur.
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The procedure given here MUST be used by anyone who wants to use a subtag not currently in the IANA Language Subtag Registry.
Only subtags of type 'language' and 'variant' will be considered for independent registration of new subtags. Handling of subtags needed for stability and subtags necessary to keep the registry synchronized with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits defined by this document are described in Section 3.3 (Maintenance of the Registry). Stability provisions are described in Section 3.4 (Stability of IANA Registry Entries).
This procedure MAY also be used to register or alter the information for the 'Description', 'Comments', 'Deprecated', 'Prefix', or 'Suppress-Script' fields in a subtag's record as described in Section 3.4 (Stability of IANA Registry Entries). Changes to all other fields in the IANA registry are NOT permitted.
Registering a new subtag or requesting modifications to an existing tag or subtag starts with the requester filling out
the registration form reproduced below. Note that each response is not limited
in size so that the request can adequately describe the registration.
The fields in the "Record Requested" section SHOULD follow the requirements in Section 3.1 (Format of the IANA Language Subtag Registry).
LANGUAGE SUBTAG REGISTRATION FORM 1. Name of requester: 2. E-mail address of requester: 3. Record Requested: Type: Subtag: Description: Prefix: Preferred-Value: Deprecated: Suppress-Script: Comments: 4. Intended meaning of the subtag: 5. Reference to published description of the language (book or article): 6. Any other relevant information:
| Figure 5: The Language Subtag Registration Form |
The subtag registration form MUST be sent to <ietf-languages@iana.org> for a two-week review period before it can be submitted to IANA. If modifications are made to the request during the course of the registration process (such as corrections to meet the requirements in Section 3.1 (Format of the IANA Language Subtag Registry)) the corrected form MUST also be sent to <ietf-languages@iana.org> prior to submission to IANA.
The ietf-languages list is an open list and can be joined by sending a request to <ietf-languages-request@iana.org>. The list can be hosted by IANA or by any third party at the request of IESG.
Variant subtags are usually registered for use with a particular range of language tags. For example, the subtag 'rozaj' is intended for use with language tags that start with the primary language subtag "sl", since Resian is a dialect of Slovenian. Thus, the subtag 'rozaj' would be appropriate in tags such as "sl-Latn-rozaj" or "sl-IT-rozaj". This information is stored in the 'Prefix' field in the registry. Variant registration requests SHOULD include at least one 'Prefix' field in the registration form.
Extended language subtags MUST include exactly one 'Prefix' field.
The 'Prefix' field for a given registered subtag exists in the IANA registry as a guide to usage. Additional prefixes MAY be added by filing an additional registration form. In that form, the "Any other relevant information:" field MUST indicate that it is the addition of a prefix.
Requests to add a prefix to a variant subtag that imply a different semantic meaning will probably be rejected. For example, a request to add the prefix "de" to the subtag 'nedis' so that the tag "de-nedis" represented some German dialect would be rejected. The 'nedis' subtag represents a particular Slovenian dialect and the additional registration would change the semantic meaning assigned to the subtag. A separate subtag SHOULD be proposed instead.
The 'Description' field MUST contain a description of the tag being registered written or transcribed into the Latin script; it MAY also include a description in a non-Latin script. Non-ASCII characters MUST be escaped using the syntax described in Section 3.1 (Format of the IANA Language Subtag Registry). The 'Description' field is used for identification purposes and doesn't necessarily represent the actual native name of the language or variation or to be in any particular language.
While the 'Description' field itself is not guaranteed to be stable and errata corrections MAY be undertaken from time to time, attempts to provide translations or transcriptions of entries in the registry itself will probably be frowned upon by the community or rejected outright, as changes of this nature have an impact on the provisions in Section 3.4 (Stability of IANA Registry Entries).
When the two-week period has passed, the Language Subtag Reviewer MUST take one of the following actions:
Forward the record to be inserted or modified to iana@iana.org according to the procedure described in Section 3.3 (Maintenance of the Registry).
Explicitly reject the request because of significant objections raised on the list or due to problems with constraints in this document (which MUST be explicitly cited)
Extend the review period by granting an additional two-week increment to permit further discussion. After each two-week increment, the Language Subtag Reviewer MUST indicate on the list whether the registration has been accepted, rejected, or extended.
Note that the Language Subtag Reviewer MAY raise objections on the list if he or she so desires. The important thing is that the objection MUST be made publicly.
Sometimes the requested record needs to be modified as a result of discussion during the review period or due to requirements in this document. The applicant, Language Subtag Reviewer, or others are free to submit a modified version of the request, which will be considered in lieu of the original request with the explicit approval of the applicant. Such changes do not restart the two-week discussion period, although an application containing the final record submitted to IANA MUST appear on the list at least one week prior to the Language Subtag Reviewer forwarding the record to IANA. The applicant is also free to modify a rejected application with additional information and submit it again; this starts a new two-week comment period.
Decisions made by the Language Subtag Reviewer MAY be appealed to the IESG [RFC2028] (Hovey, R. and S. Bradner, “The Organizations Involved in the IETF Standards Process,” October 1996.) under the same rules as other IETF decisions [RFC2026] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.). This includes a decision to extend the review period or the failure to announce a decision in a clear and timely manner.
All approved registration forms are available online in the directory http://www.iana.org/numbers.html under "languages".
Updates or changes to existing records follow the same procedure as new registrations. The Language Subtag Reviewer decides whether there is consensus to update the registration following the two week review period; normally, objections by the original registrant will carry extra weight in forming such a consensus.
Registrations are permanent and stable. Once registered, subtags will not be removed from the registry and will remain a valid way in which to specify a specific language or variant.
Note: The purpose of the "Reference to published description" section in the registration form is to aid in verifying whether a language is registered or what language or language variation a particular subtag refers to. In most cases, reference to an authoritative grammar or dictionary of that language will be useful; in cases where no such work exists, other well-known works describing that language or in that language MAY be appropriate. The Language Subtag Reviewer decides what constitutes "good enough" reference material. This requirement is not intended to exclude particular languages or dialects due to the size of the speaker population or lack of a standardized orthography. Minority languages will be considered equally on their own merits.
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Possibilities for registration of subtags or information about subtags include:
Subtags proposed for registration that would cause all or part of a grandfathered tag to become redundant but whose meaning conflicts with or alters the meaning of the grandfathered tag MUST be rejected.
This document leaves the decision on what subtags or changes to subtags are appropriate (or not) to the registration process described in Section 3.5 (Registration Procedure for Subtags).
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/iso639-2
ISO 639-3 defines a maintenance agency for additions to and changes in the list of languages in ISO 639-3. This agency is:
SIL International
ISO 639-3 Registrar
7500 W. Camp Wisdom Rd.
Dallas, TX 75236 USA
Phone: +1 972 708 7400, ext. 2293 Fax: +1 972 708 7546
Email: iso639-3@sil.org
URL: http://www.sil.org/iso639-3
The maintenance agency for ISO 3166 (country codes) is:
ISO 3166 Maintenance Agency
c/o International Organization for Standardization
Case postale 56
CH-1211 Geneva 20 Switzerland
Phone: +41 22 749 72 33 Fax: +41 22 749 73 49
URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html
The registration authority for ISO 15924 (script codes) is:
Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
URL: http://www.unicode.org/iso15924
The Statistics Division of the United Nations Secretariat maintains the Standard Country or Area Codes for Statistical Use and can be 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
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Extension subtags are those introduced by single-character subtags ("singletons") other than 'x'. They are reserved for the generation of identifiers that contain a language component and are compatible with applications that understand language tags.
The structure and form of extensions are defined by this document so that implementations can be created that are forward compatible with applications that might be created using singletons in the future. In addition, defining a mechanism for maintaining singletons will lend stability to this document by reducing the likely need for future revisions or updates.
Single-character subtags are assigned by IANA using the "IETF Consensus" policy defined by [RFC2434] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.). This policy requires the development of an RFC, which SHALL define the name, purpose, processes, and procedures for maintaining the subtags. The maintaining or registering authority, including name, contact email, discussion list email, and URL location of the registry, MUST be indicated clearly in the RFC. The RFC MUST specify or include each of the following:
IANA will maintain a registry of allocated single-character (singleton) subtags. This registry MUST use the record-jar format described by the ABNF in Section 3.1 (Format of the IANA Language Subtag Registry). 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 MUST 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, maintain the corresponding registry, or meet other conditions imposed by this section of this document MAY be appealed to the IESG [RFC2028] (Hovey, R. and S. Bradner, “The Organizations Involved in the IETF Standards Process,” October 1996.) under the same rules as other IETF decisions (see [RFC2026] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.)) 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-character subtag (singleton) assigned to the extension. The Internet-Draft submitted to define the extension SHOULD specify which letter or digit to use, although the IESG MAY change the assignment when approving the RFC.
'Description' contains the name and description of the extension.
'Comments' is an OPTIONAL field and MAY contain a broader description of the extension.
'Added' contains the date the RFC was published in the "full-date" format specified in [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.). For example: 2004-06-28 represents June 28, 2004, in the Gregorian calendar.
'RFC' contains the RFC number assigned to the extension.
'Authority' contains the name of the maintaining authority for the extension.
'Contact_Email' contains the email address used to contact the maintaining authority.
'Mailing_List' contains the URL or subscription email address of the mailing list used by the maintaining authority.
'URL' contains the URL of the registry for this extension.
The determination of whether an Internet-Draft meets the above conditions and the decision to grant or withhold such authority rests solely with the IESG and is subject to the normal review and appeals process associated with the RFC process.
Extension authors are strongly cautioned that many (including most well-formed) processors will be unaware of any special relationships or meaning inherent in the order of extension subtags. Extension authors SHOULD avoid subtag relationships or canonicalization mechanisms that interfere with matching or with length restrictions that sometimes exist in common protocols where the extension is used. In particular, applications MAY truncate the subtags in doing matching or in fitting into limited lengths, so it is RECOMMENDED that the most significant information be in the most significant (left-most) subtags and that the specification gracefully handle truncated subtags.
When a language tag is to be used in a specific, known, protocol, it is RECOMMENDED that that the language tag not contain extensions not supported by that protocol. In addition, note that some protocols MAY impose upper limits on the length of the strings used to store or transport the language tag.
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Upon adoption of this document the IANA Language Subtag Registry will need an update so that it contains the complete set of subtags valid in a language tag. This collection of subtags, along with a description of the process used to create it, is described by [registry‑update] (Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.). IANA will publi