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Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The draft header indicates that this document obsoletes RFC4646, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust Copyright Line does not match the current year == The document seems to use 'NOT RECOMMENDED' as an RFC 2119 keyword, but does not include the phrase in its RFC 2119 key words list. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (May 10, 2007) is 6196 days in the past. Is this intentional? Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10646' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO15924' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO3166-1' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO639-1' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO639-2' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO639-3' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO646' ** Obsolete normative reference: RFC 2028 (Obsoleted by RFC 9281) ** Obsolete normative reference: RFC 2434 (Obsoleted by RFC 5226) ** Downref: Normative reference to an Informational RFC: RFC 2860 ** Obsolete normative reference: RFC 4234 (Obsoleted by RFC 5234) ** Downref: Normative reference to an Informational RFC: RFC 4645 -- Obsolete informational reference (is this intentional?): RFC 1766 (Obsoleted by RFC 3066, RFC 3282) -- Obsolete informational reference (is this intentional?): RFC 3066 (Obsoleted by RFC 4646, RFC 4647) -- Obsolete informational reference (is this intentional?): RFC 4646 (Obsoleted by RFC 5646) Summary: 6 errors (**), 0 flaws (~~), 2 warnings (==), 18 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Phillips, Ed. 3 Internet-Draft Yahoo! Inc. 4 Obsoletes: 4646 (if approved) M. Davis, Ed. 5 Intended status: Best Current Google 6 Practice May 10, 2007 7 Expires: November 11, 2007 9 Tags for Identifying Languages 10 draft-ietf-ltru-4646bis-06 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on November 11, 2007. 37 Copyright Notice 39 Copyright (C) The IETF Trust (2007). 41 Abstract 43 This document describes the structure, content, construction, and 44 semantics of language tags for use in cases where it is desirable to 45 indicate the language used in an information object. It also 46 describes how to register values for use in language tags and the 47 creation of user-defined extensions for private interchange. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 52 2. The Language Tag . . . . . . . . . . . . . . . . . . . . . . . 5 53 2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 5 54 2.2. Language Subtag Sources and Interpretation . . . . . . . . 8 55 2.2.1. Primary Language Subtag . . . . . . . . . . . . . . . 9 56 2.2.2. Extended Language Subtags . . . . . . . . . . . . . . 11 57 2.2.3. Script Subtag . . . . . . . . . . . . . . . . . . . . 12 58 2.2.4. Region Subtag . . . . . . . . . . . . . . . . . . . . 13 59 2.2.5. Variant Subtags . . . . . . . . . . . . . . . . . . . 15 60 2.2.6. Extension Subtags . . . . . . . . . . . . . . . . . . 16 61 2.2.7. Private Use Subtags . . . . . . . . . . . . . . . . . 17 62 2.2.8. Grandfathered Registrations . . . . . . . . . . . . . 18 63 2.2.9. Classes of Conformance . . . . . . . . . . . . . . . . 18 64 3. Registry Format and Maintenance . . . . . . . . . . . . . . . 20 65 3.1. Format of the IANA Language Subtag Registry . . . . . . . 20 66 3.1.1. File Format . . . . . . . . . . . . . . . . . . . . . 20 67 3.1.2. Record Definitions . . . . . . . . . . . . . . . . . . 21 68 3.1.3. Subtag and Tag Fields . . . . . . . . . . . . . . . . 23 69 3.1.4. Description Field . . . . . . . . . . . . . . . . . . 24 70 3.1.5. Deprecated Field . . . . . . . . . . . . . . . . . . . 25 71 3.1.6. Preferred-Value Field . . . . . . . . . . . . . . . . 25 72 3.1.7. Prefix Field . . . . . . . . . . . . . . . . . . . . . 26 73 3.1.8. Comments Field . . . . . . . . . . . . . . . . . . . . 27 74 3.1.9. Suppress-Script Field . . . . . . . . . . . . . . . . 27 75 3.2. Language Subtag Reviewer . . . . . . . . . . . . . . . . . 27 76 3.3. Maintenance of the Registry . . . . . . . . . . . . . . . 28 77 3.4. Stability of IANA Registry Entries . . . . . . . . . . . . 29 78 3.5. Registration Procedure for Subtags . . . . . . . . . . . . 34 79 3.6. Possibilities for Registration . . . . . . . . . . . . . . 37 80 3.7. Extensions and Extensions Registry . . . . . . . . . . . . 39 81 3.8. Update of the Language Subtag Registry . . . . . . . . . . 42 82 4. Formation and Processing of Language Tags . . . . . . . . . . 43 83 4.1. Choice of Language Tag . . . . . . . . . . . . . . . . . . 43 84 4.2. Meaning of the Language Tag . . . . . . . . . . . . . . . 47 85 4.3. Length Considerations . . . . . . . . . . . . . . . . . . 48 86 4.3.1. Working with Limited Buffer Sizes . . . . . . . . . . 48 87 4.3.2. Truncation of Language Tags . . . . . . . . . . . . . 49 89 4.4. Canonicalization of Language Tags . . . . . . . . . . . . 50 90 4.5. Considerations for Private Use Subtags . . . . . . . . . . 52 91 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 53 92 5.1. Language Subtag Registry . . . . . . . . . . . . . . . . . 53 93 5.2. Extensions Registry . . . . . . . . . . . . . . . . . . . 54 94 6. Security Considerations . . . . . . . . . . . . . . . . . . . 55 95 7. Character Set Considerations . . . . . . . . . . . . . . . . . 56 96 8. Changes from RFC 4646 . . . . . . . . . . . . . . . . . . . . 57 97 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 61 98 9.1. Normative References . . . . . . . . . . . . . . . . . . . 61 99 9.2. Informative References . . . . . . . . . . . . . . . . . . 62 100 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 64 101 Appendix B. Examples of Language Tags (Informative) . . . . . . . 65 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 68 103 Intellectual Property and Copyright Statements . . . . . . . . . . 69 105 1. Introduction 107 Human beings on our planet have, past and present, used a number of 108 languages. There are many reasons why one would want to identify the 109 language used when presenting or requesting information. 111 A user's language preferences often need to be identified so that 112 appropriate processing can be applied. For example, the user's 113 language preferences in a Web browser can be used to select Web pages 114 appropriately. Language preferences can also be used to select among 115 tools (such as dictionaries) to assist in the processing or 116 understanding of content in different languages. 118 In addition, knowledge about the particular language used by some 119 piece of information content might be useful or even required by some 120 types of processing; for example, spell-checking, computer- 121 synthesized speech, Braille transcription, or high-quality print 122 renderings. 124 One means of indicating the language used is by labeling the 125 information content with an identifier or "tag". These tags can be 126 used to specify user preferences when selecting information content, 127 or for labeling additional attributes of content and associated 128 resources. 130 Tags can also be used to indicate additional language attributes of 131 content. For example, indicating specific information about the 132 dialect, writing system, or orthography used in a document or 133 resource may enable the user to obtain information in a form that 134 they can understand, or it can be important in processing or 135 rendering the given content into an appropriate form or style. 137 This document specifies a particular identifier mechanism (the 138 language tag) and a registration function for values to be used to 139 form tags. It also defines a mechanism for private use values and 140 future extension. 142 This document replaces [RFC4646], which replaced [RFC3066] and its 143 predecessor [RFC1766]. For a list of changes in this document, see 144 Section 8. 146 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 147 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 148 document are to be interpreted as described in [RFC2119]. 150 2. The Language Tag 152 Language tags are used to help identify languages, whether spoken, 153 written, signed, or otherwise signaled, for the purpose of 154 communication. This includes constructed and artificial languages, 155 but excludes languages not intended primarily for human 156 communication, such as programming languages. 158 2.1. Syntax 160 The language tag is composed of one or more parts, known as 161 "subtags". Each subtag consists of a sequence of alphanumeric 162 characters. Subtags are distinguished and separated from one another 163 by a hyphen ("-", ABNF [RFC4234] %x2D). A language tag consists of a 164 "primary language" subtag and a (possibly empty) series of subsequent 165 subtags, each of which refines or narrows the range of languages 166 identified by the overall tag. 168 Usually, each type of subtag is distinguished by length, position in 169 the tag, and content: subtags can be recognized solely by these 170 features. The only exception to this is a fixed list of 171 grandfathered tags registered under RFC 3066 [RFC3066]. This makes 172 it possible to construct a parser that can extract and assign some 173 semantic information to the subtags, even if the specific subtag 174 values are not recognized. Thus, a parser need not have an up-to- 175 date copy (or any copy at all) of the subtag registry to perform most 176 searching and matching operations. 178 The syntax of the language tag in ABNF [RFC4234] is: 180 Language-Tag = langtag 181 / privateuse ; private use tag 182 / irregular ; tags grandfathered by rule 184 langtag = (language 185 ["-" script] 186 ["-" region] 187 *("-" variant) 188 *("-" extension) 189 ["-" privateuse]) 191 language = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code 192 / 4ALPHA ; reserved for future use 193 / 5*8ALPHA ; registered language subtag 195 extlang = *3("-" 3ALPHA) ; specific ISO 639-3 codes 197 script = 4ALPHA ; ISO 15924 code 199 region = 2ALPHA ; ISO 3166 code 200 / 3DIGIT ; UN M.49 code 202 variant = 5*8alphanum ; registered variants 203 / (DIGIT 3alphanum) 205 extension = singleton 1*("-" (2*8alphanum)) 207 singleton = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT 208 ; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9" 209 ; Single alphanumerics 210 ; "x" is reserved for private use 212 privateuse = "x" 1*("-" (1*8alphanum)) 214 irregular = "en-GB-oed" / "i-ami" / "i-bnn" / "i-default" 215 / "i-enochian" / "i-hak" / "i-klingon" / "i-lux" 216 / "i-mingo" / "i-navajo" / "i-pwn" / "i-tao" 217 / "i-tay" / "i-tsu" / "sgn-BE-fr" / "sgn-BE-nl" 218 / "sgn-CH-de" 220 alphanum = (ALPHA / DIGIT) ; letters and numbers 222 Figure 1: Language Tag ABNF 224 All subtags have a maximum length of eight characters and whitespace 225 is not permitted in a language tag. There is a subtlety in the ABNF 226 production 'variant': variants starting with a digit MAY be four 227 characters long, while those starting with a letter MUST be at least 228 five characters long. For examples of language tags, see Appendix B. 230 Note Well: the ABNF syntax does not distinguish between upper and 231 lowercase. The appearance of upper and lowercase letters in the 232 varous ABNF productions above do not affect how implementations 233 interpret tags. That is, the tag "I-AMI" matches the item "i-ami" in 234 the 'irregular' production. At all times, the tags and their 235 subtags, including private use and extensions, are to be treated as 236 case insensitive: there exist conventions for the capitalization of 237 some of the subtags, but these MUST NOT be taken to carry meaning. 239 For example: 241 o [ISO639-1] recommends that language codes be written in lowercase 242 ('mn' Mongolian). 244 o [ISO3166-1] recommends that country codes be capitalized ('MN' 245 Mongolia). 247 o [ISO15924] recommends that script codes use lowercase with the 248 initial letter capitalized ('Cyrl' Cyrillic). 250 However, in the tags defined by this document, the uppercase US-ASCII 251 letters in the range 'A' through 'Z' are considered equivalent and 252 mapped directly to their US-ASCII lowercase equivalents in the range 253 'a' through 'z'. Thus, the tag "mn-Cyrl-MN" is not distinct from 254 "MN-cYRL-mn" or "mN-cYrL-Mn" (or any other combination), and each of 255 these variations conveys the same meaning: Mongolian written in the 256 Cyrillic script as used in Mongolia. 258 Although case distinctions do not carry meaning in language tags, 259 consistent formatting and presentation of the tags will aid users. 260 The format of the tags and subtags in the registry is RECOMMENDED. 261 In this format, all non-initial two-letter subtags are uppercase, all 262 non-initial four-letter subtags are titlecase, and all other subtags 263 are lowercase. 265 Note that although [RFC4234] refers to octets, the language tags 266 described in this document are sequences of characters from the US- 267 ASCII [ISO646] repertoire. Language tags MAY be used in documents 268 and applications that use other encodings, so long as these encompass 269 the US-ASCII repertoire. An example of this would be an XML document 270 that uses the UTF-16LE [RFC2781] encoding of [Unicode]. 272 2.2. Language Subtag Sources and Interpretation 274 The namespace of language tags and their subtags is administered by 275 the Internet Assigned Numbers Authority (IANA) [RFC2860] according to 276 the rules in Section 5 of this document. The Language Subtag 277 Registry maintained by IANA is the source for valid subtags: other 278 standards referenced in this section provide the source material for 279 that registry. 281 Terminology used in this document: 283 o Tag or tags refers to a complete language tag, such as 284 "sr-Latn-RS" or "az-Arab-IR". Examples of tags in this document 285 are enclosed in double-quotes ("en-US"). 287 o Subtag refers to a specific section of a tag, delimited by hyphen, 288 such as the subtag 'Hant' in "zh-Hant-CN". Examples of subtags in 289 this document are enclosed in single quotes ('Hant'). 291 o Code or codes refers to values defined in external standards (and 292 which are used as subtags in this document). For example, 'Hant' 293 is an [ISO15924] script code that was used to define the 'Hant' 294 script subtag for use in a language tag. Examples of codes in 295 this document are enclosed in single quotes ('en', 'Hant'). 297 The definitions in this section apply to the various subtags within 298 the language tags defined by this document, excepting those 299 "grandfathered" tags defined in Section 2.2.8. 301 Language tags are designed so that each subtag type has unique length 302 and content restrictions. These make identification of the subtag's 303 type possible, even if the content of the subtag itself is 304 unrecognized. This allows tags to be parsed and processed without 305 reference to the latest version of the underlying standards or the 306 IANA registry and makes the associated exception handling when 307 parsing tags simpler. 309 Subtags in the IANA registry that do not come from an underlying 310 standard can only appear in specific positions in a tag. 311 Specifically, they can only occur as primary language subtags or as 312 variant subtags. 314 Note that sequences of private use and extension subtags MUST occur 315 at the end of the sequence of subtags and MUST NOT be interspersed 316 with subtags defined elsewhere in this document. 318 Single-letter and single-digit subtags are reserved for current or 319 future use. These include the following current uses: 321 o The single-letter subtag 'x' is reserved to introduce a sequence 322 of private use subtags. The interpretation of any private use 323 subtags is defined solely by private agreement and is not defined 324 by the rules in this section or in any standard or registry 325 defined in this document. 327 o All other single-letter subtags are reserved to introduce 328 standardized extension subtag sequences as described in 329 Section 3.7. 331 The single-letter subtag 'i' is used by some grandfathered tags, such 332 as "i-default", where it always appears in the first position and 333 cannot be confused with an extension. 335 2.2.1. Primary Language Subtag 337 The primary language subtag is the first subtag in a language tag 338 (with the exception of private use and certain grandfathered tags) 339 and cannot be omitted. The following rules apply to the primary 340 language subtag: 342 1. All two-character primary language subtags were defined in the 343 IANA registry according to the assignments found in the standard 344 ISO 639 Part 1, "ISO 639-1:2002, Codes for the representation of 345 names of languages -- Part 1: Alpha-2 code" [ISO639-1], or using 346 assignments subsequently made by the ISO 639-1 registration 347 authority (RA) or governing standardization bodies. 349 2. All three-character primary language subtags were defined in the 350 IANA registry according to the assignments found in either ISO 351 639 Part 2, "ISO 639-2:1998 - Codes for the representation of 352 names of languages -- Part 2: Alpha-3 code - edition 1" 353 [ISO639-2], ISO 639 Part 3, "Codes for the representation of 354 names of languages -- Part 3: Alpha-3 code for comprehensive 355 coverage of languages" [ISO639-3], or assignments subsequently 356 made by the relevant ISO 639 registration authorities or 357 governing standardization bodies. 359 3. The subtags in the range 'qaa' through 'qtz' are reserved for 360 private use in language tags. These subtags correspond to codes 361 reserved by ISO 639-2 for private use. These codes MAY be used 362 for non-registered primary language subtags (instead of using 363 private use subtags following 'x-'). Please refer to Section 4.5 364 for more information on private use subtags. 366 4. All four-character language subtags are reserved for possible 367 future standardization. 369 5. All language subtags of 5 to 8 characters in length in the IANA 370 registry were defined via the registration process in Section 3.5 371 and MAY be used to form the primary language subtag. At the time 372 this document was created, there were no examples of this kind of 373 subtag and future registrations of this type will be discouraged: 374 primary languages are strongly RECOMMENDED for registration with 375 ISO 639, and proposals rejected by ISO 639/RA-JAC will be closely 376 scrutinized before they are registered with IANA. 378 6. The single-character subtag 'x' as the primary subtag indicates 379 that the language tag consists solely of subtags whose meaning is 380 defined by private agreement. For example, in the tag "x-fr-CH", 381 the subtags 'fr' and 'CH' SHOULD NOT be taken to represent the 382 French language or the country of Switzerland (or any other value 383 in the IANA registry) unless there is a private agreement in 384 place to do so. See Section 4.5. 386 7. The single-character subtag 'i' is used by some grandfathered 387 tags (see Section 2.2.8) such as "i-klingon" and "i-bnn". (Other 388 grandfathered tags have a primary language subtag in their first 389 position.) 391 8. Other values MUST NOT be assigned to the primary subtag except by 392 revision or update of this document. 394 Note: For languages that have both an ISO 639-1 two-character code 395 and a three character code assigned by either ISO 639-2 or ISO 639-3, 396 only the ISO 639-1 two-character code is defined in the IANA 397 registry. 399 Note: For languages that have no ISO 639-1 two-character code and for 400 which the ISO 639-2/T (Terminology) code and the ISO 639-2/B 401 (Bibliographic) codes differ, only the Terminology code is defined in 402 the IANA registry. At the time this document was created, all 403 languages that had both kinds of three-character code were also 404 assigned a two-character code; it is expected that future assignments 405 of this nature will not occur. 407 Note: To avoid problems with versioning and subtag choice as 408 experienced during the transition between RFC 1766 and RFC 3066, as 409 well as the canonical nature of subtags defined by this document, the 410 ISO 639 Registration Authority Joint Advisory Committee (ISO 639/ 411 RA-JAC) has included the following statement in [iso639.prin]: 413 "A language code already in ISO 639-2 at the point of freezing ISO 414 639-1 shall not later be added to ISO 639-1. This is to ensure 415 consistency in usage over time, since users are directed in 416 Internet applications to employ the alpha-3 code when an alpha-2 417 code for that language is not available." 419 In order to avoid instability in the canonical form of tags, if a 420 two-character code is added to ISO 639-1 for a language for which a 421 three-character code was already included in either ISO 639-2 or ISO 422 639-3, the two-character code MUST NOT be registered. See 423 Section 3.4. 425 For example, if some content were tagged with 'haw' (Hawaiian), which 426 currently has no two-character code, the tag would not be invalidated 427 if ISO 639-1 were to assign a two-character code to the Hawaiian 428 language at a later date. 430 Note: An example of independent primary language subtag registration 431 might include: one of the grandfathered IANA registrations is 432 "i-enochian". The subtag 'enochian' could be registered in the IANA 433 registry as a primary language subtag (assuming that ISO 639 does not 434 register this language first), making tags such as "enochian-AQ" and 435 "enochian-Latn" valid. 437 2.2.2. Extended Language Subtags 439 Extended language subtags are used to identify languages that are 440 encompassed by a "macrolanguage". ISO 639-3 defines certain 441 languages to be "macrolanguages"; that is, they are groups of very 442 closely related languages which are treated as a single language in 443 certain contexts. In order to improve matching behavior and tagging 444 consistency, each language encompassed by a ISO 639-3 macrolanguage 445 is represented in the IANA registry using an extended language 446 subtag, provided that it is not already represented using a language 447 subtag. The following rules apply to the extended language subtags: 449 1. These subtags were defined in the IANA registry according to 450 assignments found in ISO 639 Part 3. 452 2. A sequence of up to three extended language subtags MAY appear in 453 a language tag. This sequence MUST follow the primary language 454 subtag and precede any other subtags. 456 3. Each extended language subtag MUST only be used with the exact 457 sequence of subtags that appears in the 'Prefix' field in its 458 registry record. 460 4. Other values MUST NOT be assigned to the extended language subtag 461 except by revision or update of this document. 463 Extended language subtag records MUST include exactly one 'Prefix' 464 field indicating an appropriate subtag or sequence of subtags for 465 that extended language subtag. 467 For example, the 'gan' and 'cmn' subtags represent the languages Gan 468 Chinese and Mandarin Chinese. Each is encompassed by the 469 macrolanguage 'zh' (Chinese). Therefore, they both have the prefix 470 "zh" in their registry records. Consequently, Gan Chinese is 471 represented as "zh-gan" and Mandarin Chinese as "zh-cmn". The 472 language subtag 'zh' can still be used without an extended language 473 subtag to label a resource as some unspecified variety of Chinese 474 (which in practice will usually be Mandarin, the dominant variety of 475 Chinese, but might also be some other variety). 477 Now suppose that, in the future, the ISO 639-3 Registration Authority 478 were to decide that Gan Chinese is actually two different closely 479 related languages: it might reclassify 'gan' as a macrolanguage and 480 introduce two new code elements. In that case, these code elements 481 would be added to the IANA registry as extended language subtags with 482 prefixes of "zh-gan". No change would be made to the registry record 483 for 'gan'. 485 2.2.3. Script Subtag 487 Script subtags are used to indicate the script or writing system 488 variations that distinguish the written forms of a language or its 489 dialects. The following rules apply to the script subtags: 491 1. All four-character subtags were defined according to 492 [ISO15924]--"Codes for the representation of the names of 493 scripts": alpha-4 script codes, or subsequently assigned by the 494 ISO 15924 maintenance agency or governing standardization bodies, 495 denoting the script or writing system used in conjunction with 496 this language. 498 2. Script subtags MUST immediately follow the primary language 499 subtag and all extended language subtags and MUST occur before 500 any other type of subtag described below. 502 3. The script subtags 'Qaaa' through 'Qabx' are reserved for private 503 use in language tags. These subtags correspond to codes reserved 504 by ISO 15924 for private use. These codes MAY be used for non- 505 registered script values. Please refer to Section 4.5 for more 506 information on private use subtags. 508 4. Script subtags MUST NOT be registered using the process in 509 Section 3.5 of this document. Variant subtags MAY be considered 510 for registration for that purpose. 512 5. There MUST be at most one script subtag in a language tag, and 513 the script subtag SHOULD be omitted when it adds no 514 distinguishing value to the tag or when the primary language 515 subtag's record includes a Suppress-Script field listing the 516 applicable script subtag. 518 Example: "sr-Latn" represents Serbian written using the Latin script. 520 2.2.4. Region Subtag 522 Region subtags are used to indicate linguistic variations associated 523 with or appropriate to a specific country, territory, or region. 524 Typically, a region subtag is used to indicate regional dialects or 525 usage, or region-specific spelling conventions. A region subtag can 526 also be used to indicate that content is expressed in a way that is 527 appropriate for use throughout a region, for instance, Spanish 528 content tailored to be useful throughout Latin America. 530 The following rules apply to the region subtags: 532 1. Region subtags MUST follow any language, extended language, or 533 script subtags and MUST precede all other subtags. 535 2. All two-character subtags following the primary subtag were 536 defined in the IANA registry according to the assignments found 537 in [ISO3166-1] ("Codes for the representation of names of 538 countries and their subdivisions -- Part 1: Country codes") using 539 the list of alpha-2 country codes, or using assignments 540 subsequently made by the ISO 3166 maintenance agency or governing 541 standardization bodies. 543 3. All three-character subtags consisting of digit (numeric) 544 characters following the primary subtag were defined in the IANA 545 registry according to the assignments found in UN Standard 546 Country or Area Codes for Statistical Use [UN_M.49] or 547 assignments subsequently made by the governing standards body. 548 Note that not all of the UN M.49 codes are defined in the IANA 549 registry. The following rules define which codes are entered 550 into the registry as valid subtags: 552 A. UN numeric codes assigned to 'macro-geographical 553 (continental)' or sub-regions MUST be registered in the 554 registry. These codes are not associated with an assigned 555 ISO 3166 alpha-2 code and represent supra-national areas, 556 usually covering more than one nation, state, province, or 557 territory. 559 B. UN numeric codes for 'economic groupings' or 'other 560 groupings' MUST NOT be registered in the IANA registry and 561 MUST NOT be used to form language tags. 563 C. UN numeric codes for countries or areas with ambiguous ISO 564 3166 alpha-2 codes, when entered into the registry, MUST be 565 defined according to the rules in Section 3.4 and MUST be 566 used to form language tags that represent the country or 567 region for which they are defined. 569 D. UN numeric codes for countries or areas for which there is an 570 associated ISO 3166 alpha-2 code in the registry MUST NOT be 571 entered into the registry and MUST NOT be used to form 572 language tags. Note that the ISO 3166-based subtag in the 573 registry MUST actually be associated with the UN M.49 code in 574 question. 576 E. UN numeric codes and ISO 3166 alpha-2 codes for countries or 577 areas listed as eligible for registration in [RFC4645] but 578 not presently registered MAY be entered into the IANA 579 registry via the process described in Section 3.5. Once 580 registered, these codes MAY be used to form language tags. 582 F. All other UN numeric codes for countries or areas that do not 583 have an associated ISO 3166 alpha-2 code MUST NOT be entered 584 into the registry and MUST NOT be used to form language tags. 585 For more information about these codes, see Section 3.4. 587 4. Note: The alphanumeric codes in Appendix X of the UN document 588 MUST NOT be entered into the registry and MUST NOT be used to 589 form language tags. (At the time this document was created, 590 these values matched the ISO 3166 alpha-2 codes.) 592 5. There MUST be at most one region subtag in a language tag and the 593 region subtag MAY be omitted, as when it adds no distinguishing 594 value to the tag. 596 6. The region subtags 'AA', 'QM'-'QZ', 'XA'-'XZ', and 'ZZ' are 597 reserved for private use in language tags. These subtags 598 correspond to codes reserved by ISO 3166 for private use. These 599 codes MAY be used for private use region subtags (instead of 600 using a private use subtag sequence). Please refer to 601 Section 4.5 for more information on private use subtags. 603 "de-CH" represents German ('de') as used in Switzerland ('CH'). 605 "sr-Latn-RS" represents Serbian ('sr') written using Latin script 606 ('Latn') as used in Serbia ('RS'). 608 "es-419" represents Spanish ('es') appropriate to the UN-defined 609 Latin America and Caribbean region ('419'). 611 2.2.5. Variant Subtags 613 Variant subtags are used to indicate additional, well-recognized 614 variations that define a language or its dialects that are not 615 covered by other available subtags. The following rules apply to the 616 variant subtags: 618 1. Variant subtags are not associated with any external standard. 619 Variant subtags and their meanings are defined by the 620 registration process defined in Section 3.5. 622 2. Variant subtags MUST follow all of the other defined subtags, but 623 precede any extension or private use subtag sequences. 625 3. More than one variant MAY be used to form the language tag. 627 4. Variant subtags MUST be registered with IANA according to the 628 rules in Section 3.5 of this document before being used to form 629 language tags. In order to distinguish variants from other types 630 of subtags, registrations MUST meet the following length and 631 content restrictions: 633 1. Variant subtags that begin with a letter (a-z, A-Z) MUST be 634 at least five characters long. 636 2. Variant subtags that begin with a digit (0-9) MUST be at 637 least four characters long. 639 Variant subtag records in the language subtag registry MAY include 640 one or more 'Prefix' fields, which indicate the language tag or tags 641 that would make a suitable prefix (with other subtags, as 642 appropriate) in forming a language tag with the variant. For 643 example, the subtag 'nedis' has a Prefix of "sl", making it suitable 644 to form language tags such as "sl-nedis" and "sl-IT-nedis", but not 645 suitable for use in a tag such as "zh-nedis" or "it-IT-nedis". 647 "sl-nedis" represents the Natisone or Nadiza dialect of Slovenian. 649 "de-CH-1996" represents German as used in Switzerland and as written 650 using the spelling reform beginning in the year 1996 C.E. 652 Most variants that share a prefix are mutually exclusive. For 653 example, the German orthographic variations '1996' and '1901' SHOULD 654 NOT be used in the same tag, as they represent the dates of different 655 spelling reforms. A variant that can meaningfully be used in 656 combination with another variant SHOULD include a 'Prefix' field in 657 its registry record that lists that other variant. For example, if 658 another German variant 'example' were created that made sense to use 659 with '1996', then 'example' should include two Prefix fields: "de" 660 and "de-1996". 662 2.2.6. Extension Subtags 664 Extensions provide a mechanism for extending language tags for use in 665 various applications. See Section 3.7. The following rules apply to 666 extensions: 668 1. Extension subtags are separated from the other subtags defined 669 in this document by a single-character subtag ("singleton"). 670 The singleton MUST be one allocated to a registration authority 671 via the mechanism described in Section 3.7 and MUST NOT be the 672 letter 'x', which is reserved for private use subtag sequences. 674 2. Note: Private use subtag sequences starting with the singleton 675 subtag 'x' are described in Section 2.2.7 below. 677 3. An extension MUST follow at least a primary language subtag. 678 That is, a language tag cannot begin with an extension. 679 Extensions extend language tags, they do not override or replace 680 them. For example, "a-value" is not a well-formed language tag, 681 while "de-a-value" is. 683 4. Each singleton subtag MUST appear at most one time in each tag 684 (other than as a private use subtag). That is, singleton 685 subtags MUST NOT be repeated. For example, the tag "en-a-bbb-a- 686 ccc" is invalid because the subtag 'a' appears twice. Note that 687 the tag "en-a-bbb-x-a-ccc" is valid because the second 688 appearance of the singleton 'a' is in a private use sequence. 690 5. Extension subtags MUST meet all of the requirements for the 691 content and format of subtags defined in this document. 693 6. Extension subtags MUST meet whatever requirements are set by the 694 document that defines their singleton prefix and whatever 695 requirements are provided by the maintaining authority. 697 7. Each extension subtag MUST be from two to eight characters long 698 and consist solely of letters or digits, with each subtag 699 separated by a single '-'. 701 8. Each singleton MUST be followed by at least one extension 702 subtag. For example, the tag "tlh-a-b-foo" is invalid because 703 the first singleton 'a' is followed immediately by another 704 singleton 'b'. 706 9. Extension subtags MUST follow all language, extended language, 707 script, region, and variant subtags in a tag. 709 10. All subtags following the singleton and before another singleton 710 are part of the extension. Example: In the tag "fr-a-Latn", the 711 subtag 'Latn' does not represent the script subtag 'Latn' 712 defined in the IANA Language Subtag Registry. Its meaning is 713 defined by the extension 'a'. 715 11. In the event that more than one extension appears in a single 716 tag, the tag SHOULD be canonicalized as described in 717 Section 4.4. 719 For example, if the prefix singleton 'r' and the shown subtags were 720 defined, then the following tag would be a valid example: "en-Latn- 721 GB-boont-r-extended-sequence-x-private" 723 2.2.7. Private Use Subtags 725 Private use subtags are used to indicate distinctions in language 726 important in a given context by private agreement. The following 727 rules apply to private use subtags: 729 1. Private use subtags are separated from the other subtags defined 730 in this document by the reserved single-character subtag 'x'. 732 2. Private use subtags MUST conform to the format and content 733 constraints defined in the ABNF for all subtags. 735 3. Private use subtags MUST follow all language, extended language, 736 script, region, variant, and extension subtags in the tag. 737 Another way of saying this is that all subtags following the 738 singleton 'x' MUST be considered private use. Example: The 739 subtag 'US' in the tag "en-x-US" is a private use subtag. 741 4. A tag MAY consist entirely of private use subtags. 743 5. No source is defined for private use subtags. Use of private use 744 subtags is by private agreement only. 746 6. Private use subtags are NOT RECOMMENDED where alternatives exist 747 or for general interchange. See Section 4.5 for more information 748 on private use subtag choice. 750 For example: Users who wished to utilize codes from the Ethnologue 751 publication of SIL International for language identification might 752 agree to exchange tags such as "az-Arab-x-AZE-derbend". This example 753 contains two private use subtags. The first is 'AZE' and the second 754 is 'derbend'. 756 2.2.8. Grandfathered Registrations 758 Prior to RFC 4646, whole language tags were registered according to 759 the rules in RFC 1766 and/or RFC 3066. These registered tags 760 maintain their validity. Of those tags, those that were made 761 obsolete or redundant by the advent of RFC 4646, by this document, or 762 by subsequent registration of subtags are maintained in the registry 763 in records as "redundant" records. Those tags that do not match the 764 'langtag' production in the ABNF in this document or that contain 765 subtags that do not individually appear in the registry are 766 maintained in the registry in records of the "grandfathered" type. 768 Grandfathered tags contain one or more subtags that are not defined 769 in the Language Subtag Registry (see Section 3). Redundant tags 770 consist entirely of subtags defined above and whose independent 771 registration was superseded by [RFC4646]. For more information see 772 Section 3.8. 774 Some grandfathered tags are "regular" in that they match the 775 'langtag' production in Figure 1. In some cases, these tags could 776 become redundant if their (current unregistered) subtags were to be 777 registered (as variants, for example). In other cases, although the 778 subtags match the language tag pattern, the meaning assigned to the 779 various subtags is prohibited by rules elsewhere in this document. 780 Those tags can never become redundant. 782 The remaining grandfathered tags are "irregular" and do not match the 783 'langtag' production. These are listed in the 'irregular' production 784 in Figure 1. These grandfathered tags can never become redundant. 785 Many of these tags have been superseded by other registrations: their 786 record contains a Preferred-Value field that really ought to be used 787 to form language tags representing that value. 789 2.2.9. Classes of Conformance 791 Implementations sometimes need to describe their capabilities with 792 regard to the rules and practices described in this document. Tags 793 can be checked or verified in a number of ways, but two particular 794 classes of tag conformance are formally defined here. 796 A tag is considered "well-formed" if it conforms to the ABNF 797 (Section 2.1). Note that irregular grandfathered tags are now listed 798 in the 'irregular' production. 800 A tag is considered "valid" if it well-formed and it also satisfies 801 these conditions: 803 o The tag is either a grandfathered tag, or all of its language, 804 extended language, script, region, and variant subtags appear in 805 the IANA language subtag registry as of the particular registry 806 date. 808 o There are no duplicate singleton (extension) subtags and no 809 duplicate variant subtags. 811 o For each subtag that has a 'Prefix' field in the registry, the 812 Prefix matches the language tag using Extended Filtering 813 [RFC4647]. That is, each subtag in the Prefix is present in the 814 tag and in the same order. For example, the Prefix "zh-TW" 815 matches the tag "zh-Hant-TW". 817 Note that a tag's validity depends on the date of the registry used 818 to validate the tag. A more-recent copy of the registry might 819 contain a subtag that an older version does not. 821 A tag is considered "valid" for a given extension (Section 3.7) (as 822 of a particular version, revision, and date) if it meets the criteria 823 for "valid" above and also satisfies this condition: 825 Each subtag used in the extension part of the tag is valid 826 according to the extension. 828 3. Registry Format and Maintenance 830 This section defines the Language Subtag Registry and the maintenance 831 and update procedures associated with it, as well as a registry for 832 extensions to language tags (Section 3.7). 834 The Language Subtag Registry contains a comprehensive list of all of 835 the subtags valid in language tags. This allows implementers a 836 straightforward and reliable way to validate language tags. The 837 Language Subtag Registry will be maintained so that, except for 838 extension subtags, it is possible to validate all of the subtags that 839 appear in a language tag under the provisions of this document or its 840 revisions or successors. In addition, the meaning of the various 841 subtags will be unambiguous and stable over time. (The meaning of 842 private use subtags, of course, is not defined by the IANA registry.) 844 3.1. Format of the IANA Language Subtag Registry 846 The IANA Language Subtag Registry ("the registry") consists of a text 847 file that is machine readable in the format described in this 848 section, plus copies of the registration forms approved in accordance 849 with the process described in Section 3.5. The existing registration 850 forms for grandfathered and redundant tags taken from RFC 3066 will 851 be maintained as part of the obsolete RFC 3066 registry. The 852 remaining set of initial subtags will not have registration forms 853 created for them. 855 3.1.1. File Format 857 The registry is in the text format described below. This format was 858 based on the record-jar format described in [record-jar]. 860 Each line of text is limited to 72 characters, including all 861 whitespace. Records are separated by lines containing only the 862 sequence "%%" (%x25.25). 864 Each field can be viewed as a single, logical line of ASCII 865 characters, comprising a field-name and a field-body separated by a 866 COLON character (%x3A). For convenience, the field-body portion of 867 this conceptual entity can be split into a multiple-line 868 representation; this is called "folding". The format of the registry 869 is described by the following ABNF (per [RFC4234]): 871 registry = record *("%%" CRLF record) 872 record = 1*( field-name *SP ":" *SP field-body CRLF ) 873 field-name = (ALPHA / DIGIT) [*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)] 874 field-body = *(([*WSP CRLF] 1*WSP) 1*ASCCHAR) 875 ASCCHAR = %x21-25 / %x27-7E / UNICHAR ; Note: AMPERSAND is %x26 876 UNICHAR = "&#x" 2*6HEXDIG ";" 878 Figure 2: Registry Format ABNF 880 The sequence '..' (%x2E.2E) in a field-body denotes a range of 881 values. Such a range represents all subtags of the same length that 882 are in alphabetic or numeric order within that range, including the 883 values explicitly mentioned. For example 'a..c' denotes the values 884 'a', 'b', and 'c' and '11..13' denotes the values '11', '12', and 885 '13'. 887 Characters from outside the US-ASCII [ISO646] repertoire, as well as 888 the AMPERSAND character ("&", %x26) when it occurs in a field-body, 889 are represented by a "Numeric Character Reference" using hexadecimal 890 notation in the style used by [XML10] (see 891 ). This consists of the 892 sequence "&#x" (%x26.23.78) followed by a hexadecimal representation 893 of the character's code point in [ISO10646] followed by a closing 894 semicolon (%x3B). For example, the EURO SIGN, U+20AC, would be 895 represented by the sequence "€". Note that the hexadecimal 896 notation MAY have between two and six digits. 898 All fields whose field-body contains a date value use the "full-date" 899 format specified in [RFC3339]. For example: "2004-06-28" represents 900 June 28, 2004, in the Gregorian calendar. 902 3.1.2. Record Definitions 904 There are three types of records in the registry: "File-Date", 905 "Subtag", and "Tag" records. 907 The first record in the registry is a "File-Date" record. This 908 record contains the single field whose field-name is "File-Date" (see 909 Figure 2). The field-body of this record contains the last 910 modification date of this copy of the registry, making it possible to 911 compare different versions of the registry. The registry on the IANA 912 website is the most current. Versions with an older date than that 913 one are not up-to-date. 915 File-Date: 2004-06-28 916 %% 918 Figure 3: Example of the File-Date Record 920 Subsequent records represent either subtags or tags in the registry. 921 "Subtag" records contain a field with a field-name of "Subtag", 922 while, unsurprisingly, "Tag" records contain a field with a field- 923 name of "Tag". Each of the fields in each record MUST occur no more 924 than once, unless otherwise noted below. Each record MUST contain 925 the following fields: 927 o 'Type' 929 * Type's field-body MUST consist of one of the following strings: 930 "language", "extlang", "script", "region", "variant", 931 "grandfathered", and "redundant" and denotes the type of tag or 932 subtag. 934 o Either 'Subtag' or 'Tag' 936 * Subtag's field-body contains the subtag being defined. This 937 field MUST only appear in records of whose 'Type' has one of 938 these values: "language", "extlang", "script", "region", or 939 "variant". 941 * Tag's field-body contains a complete language tag. This field 942 MUST only appear in records whose 'Type' has one of these 943 values: "grandfathered" or "redundant". Note that the field- 944 body will always follow the 'grandfathered' production in the 945 ABNF in Section 2.1 947 o Description 949 * Description's field-body contains a non-normative description 950 of the subtag or tag. 952 o Added 954 * Added's field-body contains the date the record was added to 955 the registry. 957 Each record MAY also contain the following fields: 959 o Preferred-Value 961 * For fields of type 'script', 'region', and 'variant', 962 'Preferred-Value' contains the subtag of the same 'Type' that 963 is preferred for forming the language tag. 965 * For fields of type 'language' and 'extlang', 'Preferred-Value' 966 contains the language production (see Figure 1) that is 967 preferred when forming the language tag. This can be simply a 968 'language' subtag, or it can be a 'language' subtag followed by 969 an extended language sequence. 971 * For fields of type 'grandfathered' and 'redundant', a canonical 972 mapping to a complete language tag. 974 o Deprecated 976 * Deprecated's field-body contains the date the record was 977 deprecated. 979 o Prefix 981 * Prefix's field-body contains a language tag with which this 982 subtag MAY be used to form a new language tag, perhaps with 983 other subtags as well. This field MUST only appear in records 984 whose 'Type' field-body is 'variant' or 'extlang'. For 985 example, the 'Prefix' for the variant 'nedis' is 'sl', meaning 986 that the tags "sl-nedis" and "sl-IT-nedis" might be appropriate 987 while the tag "is-nedis" is not. 989 o Comments 991 * Comments contains additional information about the subtag, as 992 deemed appropriate for understanding the registry and 993 implementing language tags using the subtag or tag. 995 o Suppress-Script 997 * Suppress-Script contains a script subtag that SHOULD NOT be 998 used to form language tags with the associated primary language 999 subtag. This field MUST only appear in records whose 'Type' 1000 field-body is 'language'. See Section 4.1. 1002 Future versions of this document might add additional fields to the 1003 registry, so implementations SHOULD ignore fields found in the 1004 registry that are not defined in this document. 1006 3.1.3. Subtag and Tag Fields 1008 The 'Subtag' field MUST use lowercase letters to form the subtag, 1009 with two exceptions. Subtags whose 'Type' field is 'script' (in 1010 other words, subtags defined by ISO 15924) MUST use titlecase. 1011 Subtags whose 'Type' field is 'region' (in other words, subtags 1012 defined by ISO 3166) MUST use uppercase. These exceptions mirror the 1013 use of case in the underlying standards. 1015 Each subtag in the tags contained in a 'Tag' field MUST be formatted 1016 using the rules in the preceeding paragraph. That is, all subtags 1017 are lowercase except for subtags that represent script or region 1018 codes. 1020 3.1.4. Description Field 1022 The field 'Description' contains a description of the tag or subtag 1023 in the record. The 'Description' field MAY appear more than once per 1024 record, that is, there can be multiple descriptions for a given 1025 record. At least one of the 'Description' fields MUST be written or 1026 transcribed into the Latin script; additional 'Description' fields 1027 MAY also include a description in a non-Latin script. Each 1028 'Description' field MUST be unique, both within the record in which 1029 it appears and for the collection of records of the same type. 1030 Moreover, formatting variations of the same description MUST NOT 1031 occur in that specific record or in any other record of the same 1032 type. For example, while the ISO 639-1 code 'fy' contains both the 1033 descriptions "Western Frisian" and "Frisian, Western", only one of 1034 these descriptions appears in the registry. 1036 The 'Description' field is used for identification purposes and 1037 SHOULD NOT be taken to represent the actual native name of the 1038 language or variation or to be in any particular language. 1040 For records taken from a source standard (such as ISO 639 or ISO 1041 3166), the 'Description' value(s) SHOULD also be taken from the 1042 source standard. Multiple descriptions in the source standard MUST 1043 be split into separate 'Description' fields. The source standard's 1044 descriptions MAY be edited, either prior to insertion or via the 1045 registration process. For fields of type 'language' or 'extlang', 1046 the first 'Description' field appearing in the Registry corresponds 1047 to the Reference Name assigned by ISO 639-3. This helps facilitate 1048 cross-referencing between ISO 639 and the registry. 1050 When creating or updating a record due to the action of one of the 1051 source standards, the Language Subtag Reviewer SHOULD remove 1052 duplicate or redundant descriptions and MAY edit descriptions to 1053 correct irregularities in formatting (such as misspellings, 1054 inappropriate apostrophes or other punctuation, or excessive or 1055 missing spaces) prior to submitting the proposed record to the ietf- 1056 languages list. 1058 Note: Descriptions in registry entries that correspond to ISO 639, 1059 ISO 15924, ISO 3166, or UN M.49 codes are intended only to indicate 1060 the meaning of that identifier as defined in the source standard at 1061 the time it was added to the registry. The description does not 1062 replace the content of the source standard itself. The descriptions 1063 are not intended to be the English localized names for the subtags. 1065 Localization or translation of language tag and subtag descriptions 1066 is out of scope of this document. 1068 3.1.5. Deprecated Field 1070 The field 'Deprecated' MAY be added to any record via the maintenance 1071 process described in Section 3.3 or via the registration process 1072 described in Section 3.5. Usually, the addition of a 'Deprecated' 1073 field is due to the action of one of the standards bodies, such as 1074 ISO 3166, withdrawing a code. In some historical cases, it might not 1075 have been possible to reconstruct the original deprecation date. For 1076 these cases, an approximate date appears in the registry. Although 1077 valid in language tags, subtags and tags with a 'Deprecated' field 1078 are deprecated and validating processors SHOULD NOT generate these 1079 subtags. Note that a record that contains a 'Deprecated' field and 1080 no corresponding 'Preferred-Value' field has no replacement mapping. 1082 3.1.6. Preferred-Value Field 1084 The field 'Preferred-Value' contains a mapping between the record in 1085 which it appears and another tag or subtag. The value in this field 1086 is strongly RECOMMENDED as the best choice to represent the value of 1087 this record when selecting a language tag. These values form three 1088 groups: 1090 1. ISO 639 language codes that were later withdrawn in favor of 1091 other codes. These values are mostly a historical curiosity. 1093 2. ISO 3166 region codes that have been withdrawn in favor of a new 1094 code. This sometimes happens when a country changes its name or 1095 administration in such a way that warrants a new region code. 1097 3. Grandfathered or redundant tags from RFC 3066. In many cases, 1098 these tags have become obsolete because the values they represent 1099 were later encoded by ISO 639. 1101 Records that contain a 'Preferred-Value' field MUST also have a 1102 'Deprecated' field. This field contains a date of deprecation. 1103 Thus, a language tag processor can use the registry to construct the 1104 valid, non-deprecated set of subtags for a given date. In addition, 1105 for any given tag, a processor can construct the set of valid 1106 language tags that correspond to that tag for all dates up to the 1107 date of the registry. The ability to do these mappings MAY be 1108 beneficial to applications that are matching, selecting, for 1109 filtering content based on its language tags. 1111 Note that 'Preferred-Value' mappings in records of type 'region' 1112 sometimes do not represent exactly the same meaning as the original 1113 value. There are many reasons for a country code to be changed, and 1114 the effect this has on the formation of language tags will depend on 1115 the nature of the change in question. 1117 In particular, the 'Preferred-Value' field does not imply retagging 1118 content that uses the affected subtag. 1120 The field 'Preferred-Value' MUST NOT be modified once created in the 1121 registry. The field MAY be added to records according to the rules 1122 in Section 3.3. 1124 The 'Preferred-Value' field in records of type "grandfathered" and 1125 "redundant" contains whole language tags that are strongly 1126 RECOMMENDED for use in place of the record's value. In many cases, 1127 the mappings were created by deprecation of the tags during the 1128 period before this document was adopted. For example, the tag "no- 1129 nyn" was deprecated in favor of the ISO 639-1-defined language code 1130 'nn'. 1132 3.1.7. Prefix Field 1134 The field of type 'Prefix' MUST NOT be removed from any record. The 1135 field-body for this type of field MAY be modified, but only if the 1136 modification broadens the meaning of the subtag. That is, the field- 1137 body can be replaced only by a prefix a prefix of itself. For 1138 example, the Prefix "be-Latn" (Belarusian, Latin script) could be 1139 replaced by the Prefix "be" (Belarusian) but not by the Prefix "ru- 1140 Latn" (Russian, Latin script). 1142 The field-body of the 'Prefix' field consists of a language tag whose 1143 subtags are appropriate to use with this subtag. For example, the 1144 variant subtag '1996' has a 'Prefix' field of "de". This means that 1145 tags starting with the sequence "de-" are appropriate with this 1146 subtag, so "de-Latg-1996" and "de-CH-1996" are both acceptable, while 1147 the tag "fr-1996" is an inappropriate choice. 1149 Records of type 'variant' MAY have more than one field of type 1150 'Prefix'. Additional fields of this type MAY be added to a 'variant' 1151 record via the registration process. 1153 The field-body of the 'Prefix' field MUST NOT conflict with any 1154 'Prefix' already registered for a given record. Such a conflict 1155 would occur when when no valid tag could be constructed that would 1156 contain the prefix, such as when when two subtags each have a 1157 'Prefix' that contains the other subtag. For example, suppose that 1158 the subtag 'avariant' has the prefix "es-bvariant". Then the subtag 1159 'bvariant' cannot given the prefix 'avariant', for that would require 1160 a tag of the form "es-avariant-bvariant-avariant", which would not be 1161 valid. 1163 Records of type 'extlang' MUST have _exactly_ one 'Prefix' field. 1165 3.1.8. Comments Field 1167 The field 'Comments' MAY appear more than once per record. This 1168 field MAY be inserted or changed via the registration process and no 1169 guarantee of stability is provided. The content of this field is not 1170 restricted, except by the need to register the information, the 1171 suitability of the request, and by reasonable practical size 1172 limitations. 1174 3.1.9. Suppress-Script Field 1176 The field 'Suppress-Script' MUST only appear in records whose 'Type' 1177 field-body is 'language'. This field MUST NOT appear more than one 1178 time in a record. This field indicates a script used to write the 1179 overwhelming majority of documents for the given language and that 1180 therefore adds no distinguishing information to a language tag. It 1181 helps ensure greater compatibility between the language tags 1182 generated according to the rules in this document and language tags 1183 and tag processors or consumers based on RFC 3066. For example, 1184 virtually all Icelandic documents are written in the Latin script, 1185 making the subtag 'Latn' redundant in the tag "is-Latn". 1187 Many language subtag records do not have a Suppress-Script field. 1188 The lack of a Suppress-Script might indicate that the language is 1189 customarily written in more than one script or that the language is 1190 not customarily written at all. It might also mean that sufficient 1191 information was not available when the record was created and thus 1192 remains a candidate for future registration. 1194 3.2. Language Subtag Reviewer 1196 The Language Subtag Reviewer moderates the ietf-languages mailing 1197 list, responds to requests for registration, and performs the other 1198 registry maintenance duties described in Section 3.3. Only the 1199 Language Subtag Reviewer is permitted to request IANA to change, 1200 update, or add records to the Language Subtag Registry. The Language 1201 Subtag Reviewer MAY delegate list moderation and other clerical 1202 duties as needed. 1204 The Language Subtag Reviewer is appointed by the IESG for an 1205 indefinite term, subject to removal or replacement at the IESG's 1206 discretion. The IESG will solicit nominees for the position 1207 (initially or upon a vacancy) and seek to ascertain the candidates' 1208 qualifications. 1210 The subsequent performance or decisions of the Language Subtag 1211 Reviewer MAY be appealed to the IESG under the same rules as other 1212 IETF decisions (see [RFC2026]). The IESG can reverse or overturn the 1213 decision of the Language Subtag Reviewer, provide guidance, or take 1214 other appropriate actions. 1216 3.3. Maintenance of the Registry 1218 Maintenance of the registry requires that as codes are assigned or 1219 withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language 1220 Subtag Reviewer MUST evaluate each change and determine the 1221 appropriate course of action according to the rules in this document. 1222 Usually this requires that the Language Subtag Reviewer fill in and 1223 submit the registration form found in Section 3.5 for the new or 1224 updated record. If a change to one of these standards takes place 1225 and the Language Subtag Reviewer does not do this in a timely manner, 1226 then any interested party MAY submit the form to begin the 1227 registration process. Thereafter the registration process continues 1228 normally. 1230 Note: The redundant and grandfathered entries together are the 1231 complete list of tags registered under [RFC3066]. The redundant tags 1232 are those that can now be formed using the subtags defined in the 1233 registry together with the rules of Section 2.2. The grandfathered 1234 entries include those that can never be legal under those same 1235 provisions plus those tags that contain subtags not yet registered 1236 or, perhaps, inappropriate for registration. 1238 The set of redundant and grandfathered tags is permanent and stable: 1239 new entries in this section MUST NOT be added and existing entries 1240 MUST NOT be removed. Records of type 'grandfathered' MAY have their 1241 type converted to 'redundant'; see item 12 in Section 3.6 for more 1242 information. The decision-making process about which tags were 1243 initially grandfathered and which were made redundant is described in 1244 [RFC4645]. 1246 RFC 3066 tags that were deprecated prior to the adoption of [RFC4646] 1247 are part of the list of grandfathered tags, and their component 1248 subtags were not included as registered variants (although they 1249 remain eligible for registration). For example, the tag "art-lojban" 1250 was deprecated in favor of the language subtag 'jbo'. 1252 The Language Subtag Reviewer MUST ensure that new subtags meet the 1253 requirements in Section 4.1 or submit an appropriate registration 1254 form for an alternate subtag as described in that section. When 1255 either a change or addition to the registry is needed, the Language 1256 Subtag Reviewer MUST prepare the registration form and each record 1257 being modified or inserted MUST be sent to the ietf-languages list in 1258 a separate message. 1260 Upon approval of the registration, the Language Subtag Reviewer MUST 1261 forward the form containing the final record to IANA. If a record 1262 represents a new subtag that does not currently exist in the 1263 registry, then the message's subject line MUST include the word 1264 "INSERT". If the record represents a change to an existing subtag, 1265 then the subject line of the message MUST include the word "MODIFY". 1266 The message MUST contain both the form for the subtag being inserted 1267 or modified and the new File-Date record. Here is an example of what 1268 the body of the message might contain: 1270 LANGUAGE SUBTAG REGISTRATION FORM 1272 File-Date: 2005-01-02 1274 1. Name of requester: Michael Everson 1275 2. E-mail address of requester: someone@example.org 1276 3. Record Requested: 1277 %% 1278 Type: variant 1279 Subtag: nedis 1280 Description: Natisone dialect 1281 Description: Nadiza dialect 1282 Added: 2003-10-09 1283 Prefix: sl 1284 Comments: This is a comment shown 1285 as an example. 1286 %% 1287 4. Intended meaning of the subtag: Nadiza dialect of Slovenian 1288 5. Reference to published description 1289 of the language (book or article): N/A 1290 6. Any other relevant information: (none) 1292 Figure 4: Example of a Language Subtag Modification Form 1294 Whenever an entry is created or modified in the registry, the 'File- 1295 Date' record at the start of the registry is updated to reflect the 1296 most recent modification date in the [RFC3339] "full-date" format. 1298 Before forwarding a new registration to IANA, the Language Subtag 1299 Reviewer MUST ensure that values in the 'Subtag' field match case 1300 according to the description in Section 3.1. 1302 3.4. Stability of IANA Registry Entries 1304 The stability of entries and their meaning in the registry is 1305 critical to the long-term stability of language tags. The rules in 1306 this section guarantee that a specific language tag's meaning is 1307 stable over time and will not change. 1309 These rules specifically deal with how changes to codes (including 1310 withdrawal and deprecation of codes) maintained by ISO 639, ISO 1311 15924, ISO 3166, and UN M.49 are reflected in the IANA Language 1312 Subtag Registry. Assignments to the IANA Language Subtag Registry 1313 MUST follow the following stability rules: 1315 1. Values in the fields 'Type', 'Subtag', 'Tag', 'Added', 1316 'Deprecated' and 'Preferred-Value' MUST NOT be changed and are 1317 guaranteed to be stable over time. 1319 2. Values in the 'Description' field MUST NOT be changed in a way 1320 that would invalidate previously-existing tags. They MAY be 1321 broadened somewhat in scope, changed to add information, or 1322 adapted to the most common modern usage. For example, countries 1323 occasionally change their official names; a historical example 1324 of this would be "Upper Volta" changing to "Burkina Faso". 1326 3. Values in the field 'Prefix' MAY be added to records of type 1327 'variant' via the registration process. If a prefix is added to 1328 a variant record, 'Comment' fields SHOULD be used to explain 1329 different usages with the various prefixes. 1331 4. Values in the field 'Prefix' in records of type 'variant' MAY be 1332 modified, so long as the modifications broaden the set of 1333 prefixes. That is, a prefix MAY be replaced by one of its own 1334 prefixes. For example, the prefix "en-US" could be replaced by 1335 "en", but not by the prefixes "en-Latn", "fr", or "en-US-boont". 1336 If one of those prefixes were needed, a new Prefix SHOULD be 1337 registered. 1339 5. Values in the field 'Prefix' in records of type 'extlang' MUST 1340 NOT be modified. 1342 6. Values in the field 'Prefix' MUST NOT be removed. 1344 7. The field 'Comments' MAY be added, changed, modified, or removed 1345 via the registration process or any of the processes or 1346 considerations described in this section. 1348 8. The field 'Suppress-Script' MAY be added or removed via the 1349 registration process. 1351 9. Codes assigned by ISO 639-1 that do not conflict with existing 1352 two-letter primary language subtags and which have no 1353 corresponding three-letter primary or extended language subtags 1354 defined in the registry are entered into the IANA registry as 1355 new records of type 'language'. 1357 10. Codes assigned by ISO 639-2 that do not conflict with existing 1358 three-letter primary or extended language subtags are entered 1359 into the IANA registry as new records of type 'language'. 1361 11. Codes assigned by ISO 639-3 that do not conflict with existing 1362 three-letter primary or extended language subtags are entered 1363 into the IANA registry as new records. 1365 1. Codes that have a defined "macro-language" mapping at the 1366 time of their registration MUST be entered into the registry 1367 as records of type 'extlang' with a 'Prefix' field 1368 containing the appropriate prefix tag. 1370 2. Codes that represent sign languages MUST be entered into the 1371 registry as record of type 'extlang' with a 'Prefix' field 1372 that matches the Basic Language Range "sgn" (see Section 1373 3.3.1 "Basic Filtering" in [RFC4647]). 1375 3. All other codes MUST be entered into the registry as records 1376 of type 'language'. 1378 12. A record of type 'language' or 'extlang' MUST NOT be registered 1379 if there exists a record of either type with the same subtag 1380 value. For example, if an 'extlang' subtag 'foo' exists in the 1381 registry, all attempts to register a 'language' subtag 'foo' 1382 will be rejected. 1384 13. Codes assigned by ISO 15924 and ISO 3166 that do not conflict 1385 with existing subtags of the associated type and whose meaning 1386 is not the same as an existing subtag of the same type are 1387 entered into the IANA registry as new records. 1389 14. Codes assigned by ISO 639, ISO 15924, or ISO 3166 that are 1390 withdrawn by their respective maintenance or registration 1391 authority remain valid in language tags. A 'Deprecated' field 1392 containing the date of withdrawal MUST be added to the record. 1393 If a new record of the same type is added that represents a 1394 replacement value, then a 'Preferred-Value' field MAY also be 1395 added. The registration process MAY be used to add comments 1396 about the withdrawal of the code by the respective standard. 1398 Example The region code 'TL' was assigned to the country 1399 'Timor-Leste', replacing the code 'TP' (which was assigned to 1400 'East Timor' when it was under administration by Portugal). 1401 The subtag 'TP' remains valid in language tags, but its 1402 record contains the a 'Preferred-Value' of 'TL' and its field 1403 'Deprecated' contains the date the new code was assigned 1404 ('2004-07-06'). 1406 15. Codes assigned by ISO 639, ISO 15924, or ISO 3166 that conflict 1407 with existing subtags of the associated type, including subtags 1408 that are deprecated, MUST NOT be entered into the registry. The 1409 following additional considerations apply to subtag values that 1410 are reassigned: 1412 A. For ISO 639 codes, if the newly assigned code's meaning is 1413 not represented by a subtag in the IANA registry, the 1414 Language Subtag Reviewer, as described in Section 3.5, SHALL 1415 prepare a proposal for entering in the IANA registry as soon 1416 as practical a registered language subtag as an alternate 1417 value for the new code. The form of the registered language 1418 subtag will be at the discretion of the Language Subtag 1419 Reviewer and MUST conform to other restrictions on language 1420 subtags in this document. 1422 B. For all subtags whose meaning is derived from an external 1423 standard (that is, by ISO 639, ISO 15924, ISO 3166, or UN 1424 M.49), if a new meaning is assigned to an existing code and 1425 the new meaning broadens the meaning of that code, then the 1426 meaning for the associated subtag MAY be changed to match. 1427 The meaning of a subtag MUST NOT be narrowed, however, as 1428 this can result in an unknown proportion of the existing 1429 uses of a subtag becoming invalid. Note: ISO 639 1430 maintenance agency/registration authority (MA/RA) has 1431 adopted a similar stability policy. 1433 C. For ISO 15924 codes, if the newly assigned code's meaning is 1434 not represented by a subtag in the IANA registry, the 1435 Language Subtag Reviewer, as described in Section 3.5, SHALL 1436 prepare a proposal for entering in the IANA registry as soon 1437 as practical a registered variant subtag as an alternate 1438 value for the new code. The form of the registered variant 1439 subtag will be at the discretion of the Language Subtag 1440 Reviewer and MUST conform to other restrictions on variant 1441 subtags in this document. 1443 D. For ISO 3166 codes, if the newly assigned code's meaning is 1444 associated with the same UN M.49 code as another 'region' 1445 subtag, then the existing region subtag remains as the 1446 preferred value for that region and no new entry is created. 1447 A comment MAY be added to the existing region subtag 1448 indicating the relationship to the new ISO 3166 code. 1450 E. For ISO 3166 codes, if the newly assigned code's meaning is 1451 associated with a UN M.49 code that is not represented by an 1452 existing region subtag, then the Language Subtag Reviewer, 1453 as described in Section 3.5, SHALL prepare a proposal for 1454 entering the appropriate UN M.49 country code as an entry in 1455 the IANA registry. 1457 F. For ISO 3166 codes, if there is no associated UN numeric 1458 code, then the Language Subtag Reviewer SHALL petition the 1459 UN to create one. If there is no response from the UN 1460 within ninety days of the request being sent, the Language 1461 Subtag Reviewer SHALL prepare a proposal for entering in the 1462 IANA registry as soon as practical a registered variant 1463 subtag as an alternate value for the new code. The form of 1464 the registered variant subtag will be at the discretion of 1465 the Language Subtag Reviewer and MUST conform to other 1466 restrictions on variant subtags in this document. This 1467 situation is very unlikely to ever occur. 1469 16. UN M.49 has codes for both countries and areas (such as '276' 1470 for Germany) and geographical regions and sub-regions (such as 1471 '150' for Europe). UN M.49 country or area codes for which 1472 there is no corresponding ISO 3166 code SHOULD NOT be 1473 registered, except as a surrogate for an ISO 3166 code that is 1474 blocked from registration by an existing subtag. If such a code 1475 becomes necessary, then the registration authority for ISO 3166 1476 SHOULD first be petitioned to assign a code to the region. If 1477 the petition for a code assignment by ISO 3166 is refused or not 1478 acted on in a timely manner, the registration process described 1479 in Section 3.5 MAY then be used to register the corresponding UN 1480 M.49 code. This way, UN M.49 codes remain available as the 1481 value of last resort in cases where ISO 3166 reassigns a 1482 deprecated value in the registry. 1484 17. Stability provisions apply to grandfathered tags with this 1485 exception: should it be possible to compose one of the 1486 grandfathered tags from registered subtags, then the field 1487 'Type' in that record is changed from 'grandfathered' to 1488 'redundant'. Note that this will not affect language tags that 1489 match the grandfathered tag, since these tags will now match 1490 valid generative subtag sequences. For example, this document 1491 caused the ISO 639-3 code 'gan', used in the redundant tag "zh- 1492 gan", to be registered as an extended language subtag. The 1493 formerly-grandfathered tag "zh-gan" became a redundant tag as a 1494 result (but existing content or implementations that use "zh- 1495 gan" remain valid). 1497 3.5. Registration Procedure for Subtags 1499 The procedure given here MUST be used by anyone who wants to use a 1500 subtag not currently in the IANA Language Subtag Registry. 1502 Only subtags of type 'language' and 'variant' will be considered for 1503 independent registration of new subtags. Subtags needed for 1504 stability and subtags necessary to keep the registry synchronized 1505 with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits 1506 defined by this document also use this process, as described in 1507 Section 3.3. Stability provisions are described in Section 3.4. 1509 This procedure MAY also be used to register or alter the information 1510 for the 'Description', 'Comments', 'Deprecated', 'Prefix', or 1511 'Suppress-Script' fields in a subtag's record as described in 1512 Section 3.4. Changes to all other fields in the IANA registry are 1513 NOT permitted. 1515 Registering a new subtag or requesting modifications to an existing 1516 tag or subtag starts with the requester filling out the registration 1517 form reproduced below. Note that each response is not limited in 1518 size so that the request can adequately describe the registration. 1519 The fields in the "Record Requested" section SHOULD follow the 1520 requirements in Section 3.1. 1522 LANGUAGE SUBTAG REGISTRATION FORM 1523 1. Name of requester: 1524 2. E-mail address of requester: 1525 3. Record Requested: 1527 Type: 1528 Subtag: 1529 Description: 1530 Prefix: 1531 Preferred-Value: 1532 Deprecated: 1533 Suppress-Script: 1534 Comments: 1536 4. Intended meaning of the subtag: 1537 5. Reference to published description 1538 of the language (book or article): 1539 6. Any other relevant information: 1541 Figure 5: The Language Subtag Registration Form 1543 The subtag registration form MUST be sent to 1544 for a two-week review period before it can 1545 be submitted to IANA. If modifications are made to the request 1546 during the course of the registration process (such as corrections to 1547 meet the requirements in Section 3.1) the corrected form MUST also be 1548 sent to prior to submission to IANA. 1550 The ietf-languages list is an open list and can be joined by sending 1551 a request to . The list can be 1552 hosted by IANA or by any third party at the request of IESG. 1554 Variant subtags are usually registered for use with a particular 1555 range of language tags. For example, the subtag 'rozaj' is intended 1556 for use with language tags that start with the primary language 1557 subtag "sl", since Resian is a dialect of Slovenian. Thus, the 1558 subtag 'rozaj' would be appropriate in tags such as "sl-Latn-rozaj" 1559 or "sl-IT-rozaj". This information is stored in the 'Prefix' field 1560 in the registry. Variant registration requests SHOULD include at 1561 least one 'Prefix' field in the registration form. 1563 Extended language subtags MUST include exactly one 'Prefix' field. 1565 The 'Prefix' field for a given registered subtag exists in the IANA 1566 registry as a guide to usage. Additional prefixes MAY be added by 1567 filing an additional registration form. In that form, the "Any other 1568 relevant information:" field MUST indicate that it is the addition of 1569 a prefix. 1571 Requests to add a prefix to a variant subtag that imply a different 1572 semantic meaning will probably be rejected. For example, a request 1573 to add the prefix "de" to the subtag 'nedis' so that the tag "de- 1574 nedis" represented some German dialect would be rejected. The 1575 'nedis' subtag represents a particular Slovenian dialect and the 1576 additional registration would change the semantic meaning assigned to 1577 the subtag. A separate subtag SHOULD be proposed instead. 1579 The 'Description' field MUST contain a description of the tag being 1580 registered written or transcribed into the Latin script; it MAY also 1581 include a description in a non-Latin script. Non-ASCII characters 1582 MUST be escaped using the syntax described in Section 3.1. The 1583 'Description' field is used for identification purposes and doesn't 1584 necessarily represent the actual native name of the language or 1585 variation or to be in any particular language. 1587 While the 'Description' field itself is not guaranteed to be stable 1588 and errata corrections MAY be undertaken from time to time, attempts 1589 to provide translations or transcriptions of entries in the registry 1590 itself will probably be frowned upon by the community or rejected 1591 outright, as changes of this nature have an impact on the provisions 1592 in Section 3.4. 1594 When the two-week period has passed, the Language Subtag Reviewer 1595 MUST take one of the following actions: 1597 o Explicitly accept the request and forward the form containing the 1598 record to be inserted or modified to iana@iana.org according to 1599 the procedure described in Section 3.3. 1601 o Explicitly reject the request because of significant objections 1602 raised on the list or due to problems with constraints in this 1603 document (which MUST be explicitly cited). 1605 o Extend the review period by granting an additional two-week 1606 increment to permit further discussion. After each two-week 1607 increment, the Language Subtag Reviewer MUST indicate on the list 1608 whether the registration has been accepted, rejected, or extended. 1610 Note that the Language Subtag Reviewer MAY raise objections on the 1611 list if he or she so desires. The important thing is that the 1612 objection MUST be made publicly. 1614 Sometimes the request needs to be modified as a result of discussion 1615 during the review period or due to requirements in this document. 1616 The applicant, Language Subtag Reviewer, or others are free to submit 1617 a modified version of the completed registration form, which will be 1618 considered in lieu of the original request with the explicit approval 1619 of the applicant. Such changes do not restart the two-week 1620 discussion period, although an application containing the final 1621 record submitted to IANA MUST appear on the list at least one week 1622 prior to the Language Subtag Reviewer forwarding the record to IANA. 1623 The applicant is also free to modify a rejected application with 1624 additional information and submit it again; this starts a new two- 1625 week comment period. 1627 Registrations initiated due to the provisions of Section 3.3 or 1628 Section 3.4 SHALL NOT be rejected altogether (since they have to 1629 ultimately appear in the registry) and SHOULD be completed as quickly 1630 as possible. The review process allows list members to comment on 1631 the specific information in the form and the record it contains and 1632 thus help ensure that it is correct and consistent. The Language 1633 Subtag Reviewer MAY reject a specific version of the form, but MUST 1634 include in the rejection a suitable replacement, extending the review 1635 period as described above, until the form is in a format worthy of 1636 reviewer's approval. 1638 Decisions made by the Language Subtag Reviewer MAY be appealed to the 1639 IESG [RFC2028] under the same rules as other IETF decisions 1640 [RFC2026]. This includes a decision to extend the review period or 1641 the failure to announce a decision in a clear and timely manner. 1643 The approved records appear in the Language Subtag Registry. The 1644 approved registration forms are available online under 1645 http://www.iana.org/assignments/lang-subtags-templates/. 1647 Updates or changes to existing records follow the same procedure as 1648 new registrations. The Language Subtag Reviewer decides whether 1649 there is consensus to update the registration following the two week 1650 review period; normally, objections by the original registrant will 1651 carry extra weight in forming such a consensus. 1653 Registrations are permanent and stable. Once registered, subtags 1654 will not be removed from the registry and will remain a valid way in 1655 which to specify a specific language or variant. 1657 Note: The purpose of the "Reference to published description" section 1658 in the registration form is to aid in verifying whether a language is 1659 registered or what language or language variation a particular subtag 1660 refers to. In most cases, reference to an authoritative grammar or 1661 dictionary of that language will be useful; in cases where no such 1662 work exists, other well-known works describing that language or in 1663 that language MAY be appropriate. The Language Subtag Reviewer 1664 decides what constitutes "good enough" reference material. This 1665 requirement is not intended to exclude particular languages or 1666 dialects due to the size of the speaker population or lack of a 1667 standardized orthography. Minority languages will be considered 1668 equally on their own merits. 1670 3.6. Possibilities for Registration 1672 Possibilities for registration of subtags or information about 1673 subtags include: 1675 o Primary language subtags for languages not listed in ISO 639 that 1676 are not variants of any listed or registered language MAY be 1677 registered. At the time this document was created, there were no 1678 examples of this form of subtag. Before attempting to register a 1679 language subtag, there MUST be an attempt to register the language 1680 with ISO 639. Subtags MUST NOT be registered for languages 1681 defined by codes that exist in ISO 639-1, ISO 639-2, or ISO 639-3, 1682 or that are under consideration by the ISO 639 registration 1683 authorities, or that have never been attempted for registration 1684 with those authorities. If ISO 639 has previously rejected a 1685 language for registration, it is reasonable to assume that there 1686 must be additional, very compelling evidence of need before it 1687 will be registered as a primary language subtag in the IANA 1688 registry (to the extent that it is very unlikely that any subtags 1689 will be registered of this type). 1691 o Dialect or other divisions or variations within a language, its 1692 orthography, writing system, regional or historical usage, 1693 transliteration or other transformation, or distinguishing 1694 variation MAY be registered as variant subtags. An example is the 1695 'rozaj' subtag (the Resian dialect of Slovenian). 1697 o The addition or maintenance of fields (generally of an 1698 informational nature) in Tag or Subtag records as described in 1699 Section 3.1 and subject to the stability provisions in 1700 Section 3.4. This includes descriptions, comments, deprecation 1701 and preferred values for obsolete or withdrawn codes, or the 1702 addition of script or extlang information to primary language 1703 subtags. 1705 o The addition of records and related field value changes necessary 1706 to reflect assignments made by ISO 639, ISO 15924, ISO 3166, and 1707 UN M.49 as described in Section 3.4. 1709 Subtags proposed for registration that would cause all or part of a 1710 grandfathered tag to become redundant but whose meaning conflicts 1711 with or alters the meaning of the grandfathered tag MUST be rejected. 1713 This document leaves the decision on what subtags or changes to 1714 subtags are appropriate (or not) to the registration process 1715 described in Section 3.5. 1717 Note: four-character primary language subtags are reserved to allow 1718 for the possibility of alpha4 codes in some future addition to the 1719 ISO 639 family of standards. 1721 ISO 639 defines a maintenance agency for additions to and changes in 1722 the list of languages in ISO 639. This agency is: 1724 International Information Centre for Terminology (Infoterm) 1725 Aichholzgasse 6/12, AT-1120 1726 Wien, Austria 1727 Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72 1729 ISO 639-2 defines a maintenance agency for additions to and changes 1730 in the list of languages in ISO 639-2. This agency is: 1732 Library of Congress 1733 Network Development and MARC Standards Office 1734 Washington, D.C. 20540 USA 1735 Phone: +1 202 707 6237 Fax: +1 202 707 0115 1736 URL: http://www.loc.gov/standards/iso639-2 1738 ISO 639-3 defines a maintenance agency for additions to and changes 1739 in the list of languages in ISO 639-3. This agency is: 1741 SIL International 1742 ISO 639-3 Registrar 1743 7500 W. Camp Wisdom Rd. 1744 Dallas, TX 75236 USA 1745 Phone: +1 972 708 7400, ext. 2293 Fax: +1 972 708 7546 1746 Email: iso639-3@sil.org 1747 URL: http://www.sil.org/iso639-3 1749 The maintenance agency for ISO 3166 (country codes) is: 1751 ISO 3166 Maintenance Agency 1752 c/o International Organization for Standardization 1753 Case postale 56 1754 CH-1211 Geneva 20 Switzerland 1755 Phone: +41 22 749 72 33 Fax: +41 22 749 73 49 1756 URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html 1758 The registration authority for ISO 15924 (script codes) is: 1760 Unicode Consortium Box 391476 1761 Mountain View, CA 94039-1476, USA 1762 URL: http://www.unicode.org/iso15924 1764 The Statistics Division of the United Nations Secretariat maintains 1765 the Standard Country or Area Codes for Statistical Use and can be 1766 reached at: 1768 Statistical Services Branch 1769 Statistics Division 1770 United Nations, Room DC2-1620 1771 New York, NY 10017, USA 1773 Fax: +1-212-963-0623 1774 E-mail: statistics@un.org 1775 URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm 1777 3.7. Extensions and Extensions Registry 1779 Extension subtags are those introduced by single-character subtags 1780 ("singletons") other than 'x'. They are reserved for the generation 1781 of identifiers that contain a language component and are compatible 1782 with applications that understand language tags. 1784 The structure and form of extensions are defined by this document so 1785 that implementations can be created that are forward compatible with 1786 applications that might be created using singletons in the future. 1788 In addition, defining a mechanism for maintaining singletons will 1789 lend stability to this document by reducing the likely need for 1790 future revisions or updates. 1792 Single-character subtags are assigned by IANA using the "IETF 1793 Consensus" policy defined by [RFC2434]. This policy requires the 1794 development of an RFC, which SHALL define the name, purpose, 1795 processes, and procedures for maintaining the subtags. The 1796 maintaining or registering authority, including name, contact email, 1797 discussion list email, and URL location of the registry, MUST be 1798 indicated clearly in the RFC. The RFC MUST specify or include each 1799 of the following: 1801 o The specification MUST reference the specific version or revision 1802 of this document that governs its creation and MUST reference this 1803 section of this document. 1805 o The specification and all subtags defined by the specification 1806 MUST follow the ABNF and other rules for the formation of tags and 1807 subtags as defined in this document. In particular, it MUST 1808 specify that case is not significant and that subtags MUST NOT 1809 exceed eight characters in length. 1811 o The specification MUST specify a canonical representation. 1813 o The specification of valid subtags MUST be available over the 1814 Internet and at no cost. 1816 o The specification MUST be in the public domain or available via a 1817 royalty-free license acceptable to the IETF and specified in the 1818 RFC. 1820 o The specification MUST be versioned, and each version of the 1821 specification MUST be numbered, dated, and stable. 1823 o The specification MUST be stable. That is, extension subtags, 1824 once defined by a specification, MUST NOT be retracted or change 1825 in meaning in any substantial way. 1827 o The specification MUST include in a separate section the 1828 registration form reproduced in this section (below) to be used in 1829 registering the extension upon publication as an RFC. 1831 o IANA MUST be informed of changes to the contact information and 1832 URL for the specification. 1834 IANA will maintain a registry of allocated single-character 1835 (singleton) subtags. This registry MUST use the record-jar format 1836 described by the ABNF in Section 3.1. Upon publication of an 1837 extension as an RFC, the maintaining authority defined in the RFC 1838 MUST forward this registration form to iesg@ietf.org, who MUST 1839 forward the request to iana@iana.org. The maintaining authority of 1840 the extension MUST maintain the accuracy of the record by sending an 1841 updated full copy of the record to iana@iana.org with the subject 1842 line "LANGUAGE TAG EXTENSION UPDATE" whenever content changes. Only 1843 the 'Comments', 'Contact_Email', 'Mailing_List', and 'URL' fields MAY 1844 be modified in these updates. 1846 Failure to maintain this record, maintain the corresponding registry, 1847 or meet other conditions imposed by this section of this document MAY 1848 be appealed to the IESG [RFC2028] under the same rules as other IETF 1849 decisions (see [RFC2026]) and MAY result in the authority to maintain 1850 the extension being withdrawn or reassigned by the IESG. 1851 %% 1852 Identifier: 1853 Description: 1854 Comments: 1855 Added: 1856 RFC: 1857 Authority: 1858 Contact_Email: 1859 Mailing_List: 1860 URL: 1861 %% 1863 Figure 6: Format of Records in the Language Tag Extensions Registry 1865 'Identifier' contains the single-character subtag (singleton) 1866 assigned to the extension. The Internet-Draft submitted to define 1867 the extension SHOULD specify which letter or digit to use, although 1868 the IESG MAY change the assignment when approving the RFC. 1870 'Description' contains the name and description of the extension. 1872 'Comments' is an OPTIONAL field and MAY contain a broader description 1873 of the extension. 1875 'Added' contains the date the RFC was published in the "full-date" 1876 format specified in [RFC3339]. For example: 2004-06-28 represents 1877 June 28, 2004, in the Gregorian calendar. 1879 'RFC' contains the RFC number assigned to the extension. 1881 'Authority' contains the name of the maintaining authority for the 1882 extension. 1884 'Contact_Email' contains the email address used to contact the 1885 maintaining authority. 1887 'Mailing_List' contains the URL or subscription email address of the 1888 mailing list used by the maintaining authority. 1890 'URL' contains the URL of the registry for this extension. 1892 The determination of whether an Internet-Draft meets the above 1893 conditions and the decision to grant or withhold such authority rests 1894 solely with the IESG and is subject to the normal review and appeals 1895 process associated with the RFC process. 1897 Extension authors are strongly cautioned that many (including most 1898 well-formed) processors will be unaware of any special relationships 1899 or meaning inherent in the order of extension subtags. Extension 1900 authors SHOULD avoid subtag relationships or canonicalization 1901 mechanisms that interfere with matching or with length restrictions 1902 that sometimes exist in common protocols where the extension is used. 1903 In particular, applications MAY truncate the subtags in doing 1904 matching or in fitting into limited lengths, so it is RECOMMENDED 1905 that the most significant information be in the most significant 1906 (left-most) subtags and that the specification gracefully handle 1907 truncated subtags. 1909 When a language tag is to be used in a specific, known, protocol, it 1910 is RECOMMENDED that that the language tag not contain extensions not 1911 supported by that protocol. In addition, note that some protocols 1912 MAY impose upper limits on the length of the strings used to store or 1913 transport the language tag. 1915 3.8. Update of the Language Subtag Registry 1917 Upon adoption of this document the IANA Language Subtag Registry will 1918 need an update so that it contains the complete set of subtags valid 1919 in a language tag. This collection of subtags, along with a 1920 description of the process used to create it, is described by 1921 [registry-update]. IANA will publish the updated version of the 1922 registry described by this document using the instructions and 1923 content of [registry-update]. Once published by IANA, the 1924 maintenance procedures, rules, and registration processes described 1925 in this document will be available for new registrations or updates. 1927 Registrations that are in process under the rules defined in 1928 [RFC4646] when this document is adopted MUST be completed under the 1929 rules contained in this document. 1931 4. Formation and Processing of Language Tags 1933 This section addresses how to use the information in the registry 1934 with the tag syntax to choose, form, and process language tags. 1936 4.1. Choice of Language Tag 1938 The guiding principle in forming language tags is to "tag content 1939 wisely." This means that sometimes there is a choice between several 1940 possible tags for the same content and that the choice of which tag 1941 to use depends on the content and application in question. 1943 Interoperability is best served when the same language tag is used 1944 consistently to represent the same language. If an application has 1945 requirements that make the rules here inapplicable, then that 1946 application risks damaging interoperability. It is strongly 1947 RECOMMENDED that users not define their own rules for language tag 1948 choice. 1950 A subtag SHOULD only be used when it adds useful distinguishing 1951 information to the tag. Extraneous subtags interfere with the 1952 meaning, understanding, and processing of language tags. In 1953 particular, users and implementations SHOULD follow the 'Prefix' and 1954 'Suppress-Script' fields in the registry (defined in Section 3.1): 1955 these fields provide guidance on when specific additional subtags 1956 SHOULD be used or avoided in a language tag. 1958 In particular, some applications can benefit from the use of script 1959 subtags in language tags, as long as the use is consistent for a 1960 given context. Script subtags are never appropriate for unwritten 1961 content (such as audio recordings). 1963 Script subtags were not formally defined in [RFC3066] and their use 1964 can affect matching and subtag identification for implementations of 1965 RFC 3066, as these subtags appear between the primary language and 1966 region subtags. For example, if an implementation selects content 1967 using Basic Filtering [RFC4647] (originally described in Section 2.5 1968 of [RFC3066]) and the user requested the language range "en-US", 1969 content labeled "en-Latn-US" will not match the request and thus not 1970 be selected. Therefore, it is important to know when script subtags 1971 will customarily be used and when they ought not be used. In the 1972 registry, the Suppress-Script field helps ensure greater 1973 compatibility between the language tags by defining when users SHOULD 1974 NOT include a script subtag with a particular primary language 1975 subtag. 1977 Extended language subtags (type 'extlang' in the registry; see 1978 Section 3.1) also appear between the primary language and subsequent 1979 (script, region, or variant) subtags. Applications sometimes benefit 1980 from their judicious use in forming language tags. 1982 Standards, protocols, and applications that reference this document 1983 normatively but apply different rules to the ones given in this 1984 section MUST specify how language tag selection varies from the 1985 guidelines given here. 1987 The choice of subtags used to form a language tag SHOULD be guided by 1988 the following rules: 1990 1. Use as precise a tag as possible, but no more specific than is 1991 justified. Avoid using subtags that are not important for 1992 distinguishing content in an application. 1994 * For example, 'de' might suffice for tagging an email written 1995 in German, while "de-CH-1996" is probably unnecessarily 1996 precise for such a task. 1998 2. The script subtag SHOULD NOT be used to form language tags unless 1999 the script adds some distinguishing information to the tag. The 2000 field 'Suppress-Script' in the primary language record in the 2001 registry indicates script subtags that do not add distinguishing 2002 information for most applications. For example: 2004 * The subtag 'Latn' should not be used with the primary language 2005 'en' because nearly all English documents are written in the 2006 Latin script and it adds no distinguishing information. 2007 However, if a document were written in English mixing Latin 2008 script with another script such as Braille ('Brai'), then it 2009 might be appropriate to choose to indicate both scripts to aid 2010 in content selection, such as the application of a style 2011 sheet. 2013 * When labeling content that is unwritten (such as a recording 2014 of human speech), the script subtag should not be used, even 2015 if the language is customarily written in several scripts. 2016 Thus the subtitles to a movie might use the tag "zh-cmn-Hant" 2017 (Chinese, Mandarin, Traditional script), but the audio track 2018 for the same language would be tagged "zh-cmn". 2020 3. If a tag or subtag has a 'Preferred-Value' field in its registry 2021 entry, then the value of that field SHOULD be used to form the 2022 language tag in preference to the tag or subtag in which the 2023 preferred value appears. 2025 * For example, use 'he' for Hebrew in preference to 'iw'. 2027 4. [ISO639-2] has defined several codes included in the subtag 2028 registry that require additional care when choosing language 2029 tags. In most of these cases, where omitting the language tag is 2030 permitted, such omission is preferable to using these codes. 2031 Language tags SHOULD NOT incorporate these subtags as a prefix, 2032 unless the additional information conveys some value to the 2033 application. 2035 1. Use specific language subtags or subtag sequences in 2036 preference to subtags for language collections. A "language 2037 collection" is a subtag derived from one of the [ISO639-2] 2038 codes that represents multiple related languages. These 2039 codes are included as primary language subtags in the 2040 registry. For example, the code 'cmc' represents "Chamic 2041 languages". The registry contains values for each of the 2042 approximately ten individual languages represented by this 2043 collective code. Some other examples include the subtags 2044 Germanic ('ger') or Algonquian languages ('alg'). Since 2045 these codes are interpreted inclusively, content tagged with 2046 "en" (English), "de" (German), or "gsw" (Swiss German, 2047 Alemannic) could also (but SHOULD NOT) be tagged with "ger" 2048 (Germanic languages). Subtags derived from collection codes 2049 SHOULD NOT be used be used unless more specific language 2050 information is not available. Note that matching 2051 implementations generally do not understand the relationship 2052 between the collection and its encompassed languages, and so 2053 users ought not assume a subtag based on a language 2054 collection is a useful means for selecting content in its 2055 encompassed languages. 2057 2. The 'mul' (Multiple) primary language subtag is intended to 2058 identify content in multiple languages. It SHOULD NOT be 2059 used when a list of languages (such as Content-Language) or 2060 individual tags for each content element can be used instead. 2062 3. The 'und' (Undetermined) primary language subtag is intended 2063 to identify linguistic content whose language is not known. 2064 It SHOULD NOT be used unless a language tag is required and 2065 language information is not available or cannot be 2066 determined. Omitting the language tag (where permitted) is 2067 preferred. The 'und' subtag MAY be useful for protocols that 2068 require a language tag to be provided or where a primary 2069 language subtag is required (such as in "und-Latn"). The 2070 'und' subtag MAY also be useful when matching language tags 2071 in certain situations. 2073 4. The 'zxx' (Non-Linguistic) primary language subtag is 2074 intended to identify content that has no language. Some 2075 examples might include instrumental or electronic music; 2076 sound recordings consisting of nonverbal sounds; audiovisual 2077 materials with no narration, printed titles, or subtitles; 2078 machine-readable data files consisting of machine languages 2079 or character codes; or programming source code. Note: where 2080 there are fragments of linguistic content, such as 2081 programming source code containing comments written in 2082 English, the subtag 'zxx' might still be used to indicate the 2083 primary status of the content, just as 'en' can be applied to 2084 a predominantly English text that contains a few French 2085 phrases. 2087 5. The 'mis' (Miscellaneous) primary language subtag is derived 2088 from a collective code and is used to identify linguistic 2089 content whose language is known but cannot otherwise be 2090 identified. It is commonly used when the range of language 2091 tags is constrained or for languages not otherwise 2092 categorized. For example, a library application might be 2093 limited to the set of subtags defined for use by the [MARC21] 2094 standard. The 'mis' subtag might be used by this application 2095 for languages not included in that set. It SHOULD NOT be 2096 used unless a language tag is required and no other means of 2097 identifying the language is available. 2099 6. The grandfathered tag "i-default" (Default Language) was 2100 originally registered according to [RFC1766] to meet the 2101 needs of [RFC2277]. It is used to indicate not a specific 2102 language, but rather, it identifies the condition or content 2103 used where the language preferences of the user cannot be 2104 established. It SHOULD NOT be used except as a means of 2105 labeling the default content for applications or protocols 2106 that require default language content to be labeled with that 2107 specific tag. It MAY also be used by an application or 2108 protocol to identify when the default language content is 2109 being returned. 2111 5. The same variant subtag MUST NOT be used more than once within a 2112 language tag. 2114 * For example, the tag "de-DE-1901-1901" is not valid. 2116 To ensure consistent backward compatibility, this document contains 2117 several provisions to account for potential instability in the 2118 standards used to define the subtags that make up language tags. 2119 These provisions mean that no language tag created under the rules in 2120 this document will become invalid. 2122 4.2. Meaning of the Language Tag 2124 The relationship between the tag and the information it relates to is 2125 defined by the context in which the tag appears. Accordingly, this 2126 section gives only possible examples of its usage. 2128 o For a single information object, the associated language tags 2129 might be interpreted as the set of languages that is necessary for 2130 a complete comprehension of the complete object. Example: Plain 2131 text documents. 2133 o For an aggregation of information objects, the associated language 2134 tags could be taken as the set of languages used inside components 2135 of that aggregation. Examples: Document stores and libraries. 2137 o For information objects whose purpose is to provide alternatives, 2138 the associated language tags could be regarded as a hint that the 2139 content is provided in several languages and that one has to 2140 inspect each of the alternatives in order to find its language or 2141 languages. In this case, the presence of multiple tags might not 2142 mean that one needs to be multi-lingual to get complete 2143 understanding of the document. Example: MIME multipart/ 2144 alternative. 2146 o In markup languages, such as HTML and XML, language information 2147 can be added to each part of the document identified by the markup 2148 structure (including the whole document itself). For example, one 2149 could write C'est la vie. inside a 2150 Norwegian document; the Norwegian-speaking user could then access 2151 a French-Norwegian dictionary to find out what the marked section 2152 meant. If the user were listening to that document through a 2153 speech synthesis interface, this formation could be used to signal 2154 the synthesizer to appropriately apply French text-to-speech 2155 pronunciation rules to that span of text, instead of applying the 2156 inappropriate Norwegian rules. 2158 Language tags are related when they contain a similar sequence of 2159 subtags. For example, if a language tag B contains language tag A as 2160 a prefix, then B is typically "narrower" or "more specific" than A. 2161 Thus, "zh-Hant-TW" is more specific than "zh-Hant". 2163 This relationship is not guaranteed in all cases: specifically, 2164 languages that begin with the same sequence of subtags are NOT 2165 guaranteed to be mutually intelligible, although they might be. For 2166 example, the tag "az" shares a prefix with both "az-Latn" 2167 (Azerbaijani written using the Latin script) and "az-Cyrl" 2168 (Azerbaijani written using the Cyrillic script). A person fluent in 2169 one script might not be able to read the other, even though the text 2170 might be identical. Content tagged as "az" most probably is written 2171 in just one script and thus might not be intelligible to a reader 2172 familiar with the other script. 2174 4.3. Length Considerations 2176 There is no defined upper limit on the size of language tags. While 2177 historically most language tags have consisted of language and region 2178 subtags with a combined total length of up to six characters, larger 2179 tags have always been both possible and actually appeared in use. 2181 Neither the language tag syntax nor other requirements in this 2182 document impose a fixed upper limit on the number of subtags in a 2183 language tag (and thus an upper bound on the size of a tag). The 2184 language tag syntax suggests that, depending on the specific 2185 language, more subtags (and thus a longer tag) are sometimes 2186 necessary to completely identify the language for certain 2187 applications; thus, it is possible to envision long or complex subtag 2188 sequences. 2190 4.3.1. Working with Limited Buffer Sizes 2192 Some applications and protocols are forced to allocate fixed buffer 2193 sizes or otherwise limit the length of a language tag. A conformant 2194 implementation or specification MAY refuse to support the storage of 2195 language tags that exceed a specified length. Any such limitation 2196 SHOULD be clearly documented, and such documentation SHOULD include 2197 what happens to longer tags (for example, whether an error value is 2198 generated or the language tag is truncated). A protocol that allows 2199 tags to be truncated at an arbitrary limit, without giving any 2200 indication of what that limit is, has the potential for causing harm 2201 by changing the meaning of tags in substantial ways. 2203 In practice, most language tags do not require more than a few 2204 subtags and will not approach reasonably sized buffer limitations; 2205 see Section 4.1. 2207 Some specifications or protocols have limits on tag length but do not 2208 have a fixed length limitation. For example, [RFC2231] has no 2209 explicit length limitation: the length available for the language tag 2210 is constrained by the length of other header components (such as the 2211 charset's name) coupled with the 76-character limit in [RFC2047]. 2212 Thus, the "limit" might be 50 or more characters, but it could 2213 potentially be quite small. 2215 The considerations for assigning a buffer limit are: 2217 Implementations SHOULD NOT truncate language tags unless the 2218 meaning of the tag is purposefully being changed, or unless the 2219 tag does not fit into a limited buffer size specified by a 2220 protocol for storage or transmission. 2222 Implementations SHOULD warn the user when a tag is truncated since 2223 truncation changes the semantic meaning of the tag. 2225 Implementations of protocols or specifications that are space 2226 constrained but do not have a fixed limit SHOULD use the longest 2227 possible tag in preference to truncation. 2229 Protocols or specifications that specify limited buffer sizes for 2230 language tags MUST allow for language tags of up to 33 characters. 2232 Protocols or specifications that specify limited buffer sizes for 2233 language tags SHOULD allow for language tags of at least 42 2234 characters. 2236 The following illustration shows how the 42-character recommendation 2237 was derived. The combination of language and extended language 2238 subtags was chosen for future compatibility. At up to 15 characters, 2239 this combination is longer than the longest possible primary language 2240 subtag (8 characters): 2242 language = 3 (ISO 639-2; ISO 639-1 requires 2) 2243 extlang1 = 4 (each subsequent subtag includes '-') 2244 extlang2 = 4 (unlikely: needs prefix="language-extlang1") 2245 extlang3 = 4 (extremely unlikely) 2246 script = 5 (if not suppressed: see Section 4.1) 2247 region = 4 (UN M.49; ISO 3166 requires 3) 2248 variant1 = 9 (needs 'language' as a prefix) 2249 variant2 = 9 (needs 'language-variant1' as a prefix) 2251 total = 42 characters 2253 Figure 7: Derivation of the Limit on Tag Length 2255 4.3.2. Truncation of Language Tags 2257 Truncation of a language tag alters the meaning of the tag, and thus 2258 SHOULD be avoided. However, truncation of language tags is sometimes 2259 necessary due to limited buffer sizes. Such truncation MUST NOT 2260 permit a subtag to be chopped off in the middle or the formation of 2261 invalid tags (for example, one ending with the "-" character). 2263 This means that applications or protocols that truncate tags MUST do 2264 so by progressively removing subtags along with their preceding "-" 2265 from the right side of the language tag until the tag is short enough 2266 for the given buffer. If the resulting tag ends with a single- 2267 character subtag, that subtag and its preceding "-" MUST also be 2268 removed. For example: 2270 Tag to truncate: zh-Latn-CN-variant1-a-extend1-x-wadegile-private1 2271 1. zh-Latn-CN-variant1-a-extend1-x-wadegile 2272 2. zh-Latn-CN-variant1-a-extend1 2273 3. zh-Latn-CN-variant1 2274 4. zh-Latn-CN 2275 5. zh-Latn 2276 6. zh 2278 Figure 8: Example of Tag Truncation 2280 4.4. Canonicalization of Language Tags 2282 Since a particular language tag is sometimes used by many processes, 2283 language tags SHOULD always be created or generated in a canonical 2284 form. 2286 A language tag is in canonical form when: 2288 1. The tag is well-formed according the rules in Section 2.1 and 2289 Section 2.2. 2291 2. Subtags of type 'Region' that have a Preferred-Value mapping in 2292 the IANA registry (see Section 3.1) SHOULD be replaced with their 2293 mapped value. Note: In rare cases, the mapped value will also 2294 have a Preferred-Value. 2296 3. Redundant or grandfathered tags that have a Preferred-Value 2297 mapping in the IANA registry (see Section 3.1) MUST be replaced 2298 with their mapped value. These items either are deprecated 2299 mappings created before the adoption of this document (such as 2300 the mapping of "no-nyn" to "nn" or "i-klingon" to "tlh") or are 2301 the result of later registrations or additions to this document 2302 (for example, "zh-hakka" was deprecated in favor of the language- 2303 extlang combination "zh-hak" when this document was adopted). 2305 4. Other subtags that have a Preferred-Value mapping in the IANA 2306 registry (see Section 3.1) MUST be replaced with their mapped 2307 value. These items consist entirely of clerical corrections to 2308 ISO 639-1 in which the deprecated subtags have been maintained 2309 for compatibility purposes. 2311 5. If more than one extension subtag sequence exists, the extension 2312 sequences are ordered into case-insensitive ASCII order by 2313 singleton subtag. 2315 Example: The language tag "en-A-aaa-B-ccc-bbb-x-xyz" is in canonical 2316 form, while "en-B-ccc-bbb-A-aaa-X-xyz" is well-formed but not in 2317 canonical form. 2319 Example: The language tag "en-BU" (English as used in Burma) is not 2320 canonical because the 'BU' subtag has a canonical mapping to 'MM' 2321 (Myanmar), although the tag "en-BU" maintains its validity. 2323 Canonicalization of language tags does not imply anything about the 2324 use of upper or lowercase letters when processing or comparing 2325 subtags (and as described in Section 2.1). All comparisons MUST be 2326 performed in a case-insensitive manner. 2328 When performing canonicalization of language tags, processors MAY 2329 regularize the case of the subtags (that is, this process is 2330 OPTIONAL), following the case used in the registry. Note that this 2331 corresponds to the following casing rules: uppercase all non-initial 2332 two-letter subtags; titlecase all non-initial four-letter subtags; 2333 lowercase everything else. 2335 Note: Case folding of ASCII letters in certain locales, unless 2336 carefully handled, sometimes produces non-ASCII character values. 2337 The Unicode Character Database file "SpecialCasing.txt" defines the 2338 specific cases that are known to cause problems with this. In 2339 particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is 2340 uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE). 2341 Implementers SHOULD specify a locale-neutral casing operation to 2342 ensure that case folding of subtags does not produce this value, 2343 which is illegal in language tags. For example, if one were to 2344 uppercase the region subtag 'in' using Turkish locale rules, the 2345 sequence U+0130 U+004E would result instead of the expected 'IN'. 2347 Note: if the field 'Deprecated' appears in a registry record without 2348 an accompanying 'Preferred-Value' field, then that tag or subtag is 2349 deprecated without a replacement. Validating processors SHOULD NOT 2350 generate tags that include these values, although the values are 2351 canonical when they appear in a language tag. 2353 An extension MUST define any relationships that exist between the 2354 various subtags in the extension and thus MAY define an alternate 2355 canonicalization scheme for the extension's subtags. Extensions MAY 2356 define how the order of the extension's subtags are interpreted. For 2357 example, an extension could define that its subtags are in canonical 2358 order when the subtags are placed into ASCII order: that is, "en-a- 2359 aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension might 2360 define that the order of the subtags influences their semantic 2361 meaning (so that "en-b-ccc-bbb-aaa" has a different value from "en-b- 2362 aaa-bbb-ccc"). However, extension specifications SHOULD be designed 2363 so that they are tolerant of the typical processes described in 2364 Section 3.7. 2366 4.5. Considerations for Private Use Subtags 2368 Private use subtags, like all other subtags, MUST conform to the 2369 format and content constraints in the ABNF. Private use subtags have 2370 no meaning outside the private agreement between the parties that 2371 intend to use or exchange language tags that employ them. The same 2372 subtags MAY be used with a different meaning under a separate private 2373 agreement. They SHOULD NOT be used where alternatives exist and 2374 SHOULD NOT be used in content or protocols intended for general use. 2376 Private use subtags are simply useless for information exchange 2377 without prior arrangement. The value and semantic meaning of private 2378 use tags and of the subtags used within such a language tag are not 2379 defined by this document. 2381 Subtags defined in the IANA registry as having a specific private use 2382 meaning convey more information that a purely private use tag 2383 prefixed by the singleton subtag 'x'. For applications, this 2384 additional information MAY be useful. 2386 For example, the region subtags 'AA', 'ZZ', and in the ranges 2387 'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166 private use codes) MAY 2388 be used to form a language tag. A tag such as "zh-Hans-XQ" conveys a 2389 great deal of public, interchangeable information about the language 2390 material (that it is Chinese in the simplified Chinese script and is 2391 suitable for some geographic region 'XQ'). While the precise 2392 geographic region is not known outside of private agreement, the tag 2393 conveys far more information than an opaque tag such as "x-someLang", 2394 which contains no information about the language subtag or script 2395 subtag outside of the private agreement. 2397 However, in some cases content tagged with private use subtags MAY 2398 interact with other systems in a different and possibly unsuitable 2399 manner compared to tags that use opaque, privately defined subtags, 2400 so the choice of the best approach sometimes depends on the 2401 particular domain in question. 2403 5. IANA Considerations 2405 This section deals with the processes and requirements necessary for 2406 IANA to undertake to maintain the subtag and extension registries as 2407 defined by this document and in accordance with the requirements of 2408 [RFC2434]. 2410 The impact on the IANA maintainers of the two registries defined by 2411 this document will be a small increase in the frequency of new 2412 entries or updates. 2414 5.1. Language Subtag Registry 2416 Upon adoption of this document, IANA will update the registry using 2417 instructions and content provided in a companion document: 2418 [registry-update]. The criteria and process for selecting the 2419 updated set of records are described in that document. The updated 2420 set of records represents no impact on IANA, since the work to create 2421 it will be performed externally. 2423 Future work on the Language Subtag Registry has been limited to 2424 inserting or replacing whole records preformatted for IANA by the 2425 Language Subtag Reviewer as described in Section 3.3 of this document 2426 and archiving and making publically available the forwarded 2427 registration form. 2429 Each registration form sent to IANA contains a single record for 2430 incorporation into the registry. The form MUST be sent to 2431 iana@iana.org by the Language Subtag Reviewer. It will have a 2432 subject line indicating whether the enclosed form represents an 2433 insertion of a new record (indicated by the word "INSERT" in the 2434 subject line) or a replacement of an existing record (indicated by 2435 the word "MODIFY" in the subject line). Records MUST NOT be deleted 2436 from the registry. 2438 IANA MUST extract the record from the form and place the inserted or 2439 modified record into the appropriate section of the language subtag 2440 registry, grouping the records by their 'Type' field. Inserted 2441 records MAY be placed anywhere in the appropriate section; there is 2442 no guarantee of the order of the records beyond grouping them 2443 together by 'Type'. Modified records MUST overwrite the record they 2444 replace. 2446 IANA MUST update the File-Date record to contain the most recent 2447 modification date when performing any inserting or modification: 2448 included in any request to insert or modify records will be a new 2449 File-Date record indicating the acceptance date of the record. This 2450 record MUST be placed first in the registry, replacing the existing 2451 File-Date record. In the event that the File-Date record present in 2452 the registry has a later date than the record being inserted or 2453 modified, then the latest (most recent) record MUST be preserved. 2454 IANA SHOULD process multiple registration requests in order according 2455 to the File-Date in the form, since one registration could otherwise 2456 cause a more recent change to be overwritten. 2458 The registration form sent to IANA MUST be archived and made publicly 2459 available from 2460 "http://www.iana.org/assignments/lang-subtags-templates/". Note that 2461 multiple registrations can pertain to the same record in the 2462 registry. 2464 5.2. Extensions Registry 2466 The Language Tag Extensions Registry can contain at most 35 records 2467 and thus changes to this registry are expected to be very infrequent. 2469 Future work by IANA on the Language Tag Extensions Registry is 2470 limited to two cases. First, the IESG MAY request that new records 2471 be inserted into this registry from time to time. These requests 2472 MUST include the record to insert in the exact format described in 2473 Section 3.7. In addition, there MAY be occasional requests from the 2474 maintaining authority for a specific extension to update the contact 2475 information or URLs in the record. These requests MUST include the 2476 complete, updated record. IANA is not responsible for validating the 2477 information provided, only that it is properly formatted. It should 2478 reasonably be seen to come from the maintaining authority named in 2479 the record present in the registry. 2481 6. Security Considerations 2483 Language tags used in content negotiation, like any other information 2484 exchanged on the Internet, might be a source of concern because they 2485 might be used to infer the nationality of the sender, and thus 2486 identify potential targets for surveillance. 2488 This is a special case of the general problem that anything sent is 2489 visible to the receiving party and possibly to third parties as well. 2490 It is useful to be aware that such concerns can exist in some cases. 2492 The evaluation of the exact magnitude of the threat, and any possible 2493 countermeasures, is left to each application protocol (see BCP 72 2494 [RFC3552] for best current practice guidance on security threats and 2495 defenses). 2497 The language tag associated with a particular information item is of 2498 no consequence whatsoever in determining whether that content might 2499 contain possible homographs. The fact that a text is tagged as being 2500 in one language or using a particular script subtag provides no 2501 assurance whatsoever that it does not contain characters from scripts 2502 other than the one(s) associated with or specified by that language 2503 tag. 2505 Since there is no limit to the number of variant, private use, and 2506 extension subtags, and consequently no limit on the possible length 2507 of a tag, implementations need to guard against buffer overflow 2508 attacks. See Section 4.3 for details on language tag truncation, 2509 which can occur as a consequence of defenses against buffer overflow. 2511 Although the specification of valid subtags for an extension (see 2512 Section 3.7) MUST be available over the Internet, implementations 2513 SHOULD NOT mechanically depend on it being always accessible, to 2514 prevent denial-of-service attacks. 2516 7. Character Set Considerations 2518 The syntax in this document requires that language tags use only the 2519 characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most 2520 character sets, so the composition of language tags should not have 2521 any character set issues. 2523 Rendering of characters based on the content of a language tag is not 2524 addressed in this memo. Historically, some languages have relied on 2525 the use of specific character sets or other information in order to 2526 infer how a specific character should be rendered (notably this 2527 applies to language- and culture-specific variations of Han 2528 ideographs as used in Japanese, Chinese, and Korean). When language 2529 tags are applied to spans of text, rendering engines sometimes use 2530 that information in deciding which font to use in the absence of 2531 other information, particularly where languages with distinct writing 2532 traditions use the same characters. 2534 8. Changes from RFC 4646 2536 The main goal for this revision of this document was to incorporate 2537 ISO 639-3 and its attendent set of language codes into the IANA 2538 Language Subtag Registry, permitting the identification of many more 2539 languages and dialects than previously supported. 2541 The specific changes in this document to meet these goals are: 2543 o Defines the incorporation of ISO 639-3 codes as language and 2544 extlang subtags. Extlangs are now permitted in language tags. 2545 The changes necessary to achieve this were: 2547 * something 2549 o Changed the ABNF related to grandfathered tags. The irregular 2550 tags are now listed. Well-formed grandfathered tags are now 2551 described by the 'langtag' production and the 'grandfathered' 2552 production was removed as a result. Also: added description of 2553 both types of grandfathered tags to Section 2.2.8. 2555 o Added the paragraph on "collections" to Section 4.1. 2557 o Changed the capitalization rules for 'Tag' fields in Section 3.1. 2559 o Split section 3.1 up into subsections. 2561 o Modified section 3.5 to allow Suppress-Script fields to be added, 2562 modified, or removed via the registration process. This was an 2563 erratum from RFC 4646. 2565 o Modified examples that used region code 'CS' (formerly Serbia and 2566 Montenegro) to use 'RS' (Serbia) instead. 2568 o Modified the rules for creating and maintaining record 2569 'Description' fields to prevent duplicates, including inverted 2570 duplicates. 2572 o Removed the lengthy description of why RFC 4646 was created from 2573 this section, which also caused the removal of the reference to 2574 XML Schema. 2576 o Modified the text in section 2.1 to place more emphasis on the 2577 fact that language tags are not case sensitive. 2579 o Replaced the example "fr-Latn-CA" in Section 2.1 with "sr-Latn-RS" 2580 and "az-Arab-IR" because "fr-Latn-CA" doesn't respect the 2581 Suppress-Script on 'Latn' with 'fr'. 2583 o Changed the requirements for well-formedness to make singleton 2584 repetition checking optional (it is required for validity 2585 checking) in Section 2.2.9. 2587 o Changed the text in Section 2.2.9 refering to grandfathered 2588 checking to note that the list is now included in the ABNF. 2590 o Modified and added text to Section 3.2. The job description was 2591 placed first. A note was added making clear that the Language 2592 Subtag Reviewer may delegate various non-critical duties, 2593 including list moderation. Finally, additional text was added to 2594 make the appointment process clear and to clarify that decisions 2595 and performance of the reviewer are appealable. 2597 o Added text to Section 3.5 clarifying that the ietf-languages list 2598 is operated by whomever the IESG appoints. 2600 o Added text to Section 3.1.4 clarifying that the first Description 2601 in a 'language' or 'extlang' record matches the corresponding 2602 Reference Name for the language in ISO 639-3. 2604 o Modified Section 2.2.9 to define classes of conformance related to 2605 specific tags (formerly 'well-formed' and 'valid' referred to 2606 implementations). 2608 o Added text to the end of Section 3.1.2 noting that future versions 2609 of this document might add new field types and recommending that 2610 implementations ignore any unrecognized fields. 2612 o Modified the 'extlang' examples in Appendix A to use valid subtags 2613 and removed the note saying that they were only examples. 2615 o Added text about what the lack of a Suppress-Script field means in 2616 a record to Section 3.1.9. 2618 o Added text allowing the correction of misspellings and typographic 2619 errors to Section 3.1.4. 2621 o Added text to Section 3.1.7 disallowing Prefix field conflicts 2622 (such as circular prefix references). 2624 o Modified text in Section 3.5 to require the subtag reviewer to 2625 announce his/her decision (or extension) following the two-week 2626 period. Also clarified that any decision or failure to decide can 2627 be appealed. 2629 o Modified text in Section 4.1 to include the (heretofore anecdotal) 2630 guiding principle of tag choice, and clarifying the non-use of 2631 script subtags in non-written applications. Also updated examples 2632 in this section to use Chamic languages as an example of language 2633 collections. 2635 o Prohibited multiple use of the same variant in a tag (i.e. "de- 2636 1901-1901"). Previously this was only a recommendation 2637 ("SHOULD"). 2639 o Removed inappropriate [RFC2119] language from the illustration in 2640 Section 4.3.1. 2642 o Replaced the example of "zh-gouyu" with "zh-hakka"->"zh-hak" in 2643 Section 4.4, noting that it was this document that caused the 2644 change. 2646 o Replaced the section in Section 4.1 dealing with "mul"/"und" to 2647 include the subtags 'zxx' and 'mis', as well as the tag 2648 "i-default". A normative reference to RFC 2277 was added, along 2649 with an informative reference to MARC21. 2651 o Added text to Section 3.5 clarifying that any modifications of a 2652 registration request must be sent to the ietf-languages list 2653 before submission to IANA. 2655 o Changed the ABNF for the record-jar format from using the LWSP 2656 production to use the FWS production intead. This effectively 2657 prevents blank lines in the file. 2659 o Clarified and revised text in Section 3.3, Section 3.5, and 2660 Section 5.1 to clarify that the Language Subtag Reviewer sends the 2661 complete registration forms to IANA, that IANA extracts the record 2662 from the form, and that the forms must also be archived separately 2663 from the registry. 2665 [[Ed.Note: Open issues in this version: 2667 Whether encompassed language rules for the creation of extlang 2668 records in the registry should be retained or modified. 2670 Modification of the registry to use UTF-8 as its character 2671 encoding. (removed and apparently rejected) 2673 Details of the appointment, term duration, performance review of 2674 the subtag reviewer by the IESG. (addressed?) 2676 Inclusion of additional information related to Suppress-Script in 2677 the registry (e.g. that it wasn't assigned on purpose) 2679 ]] 2681 9. References 2683 9.1. Normative References 2685 [ISO10646] 2686 International Organization for Standardization, "ISO/IEC 2687 10646:2003. Information technology -- Universal Multiple- 2688 Octet Coded Character Set (UCS)", 2003. 2690 [ISO15924] 2691 International Organization for Standardization, "ISO 2692 15924:2004. Information and documentation -- Codes for the 2693 representation of names of scripts", January 2004. 2695 [ISO3166-1] 2696 International Organization for Standardization, "ISO 3166- 2697 1:1997. Codes for the representation of names of countries 2698 and their subdivisions -- Part 1: Country codes", 1997. 2700 [ISO639-1] 2701 International Organization for Standardization, "ISO 639- 2702 1:2002. Codes for the representation of names of languages 2703 -- Part 1: Alpha-2 code", 2002. 2705 [ISO639-2] 2706 International Organization for Standardization, "ISO 639- 2707 2:1998. Codes for the representation of names of languages 2708 -- Part 2: Alpha-3 code, first edition", 1998. 2710 [ISO639-3] 2711 International Organization for Standardization, "ISO 639- 2712 3:2007. Codes for the representation of names of languages 2713 -- Part 3: Alpha-3 code for comprehensive coverage of 2714 languages", 2007. 2716 [ISO646] International Organization for Standardization, "ISO/IEC 2717 646:1991, Information technology -- ISO 7-bit coded 2718 character set for information interchange.", 1991. 2720 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 2721 3", BCP 9, RFC 2026, October 1996. 2723 [RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in 2724 the IETF Standards Process", BCP 11, RFC 2028, 2725 October 1996. 2727 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2728 Requirement Levels", BCP 14, RFC 2119, March 1997. 2730 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and 2731 Languages", BCP 18, RFC 2277, January 1998. 2733 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2734 IANA Considerations Section in RFCs", BCP 26, RFC 2434, 2735 October 1998. 2737 [RFC2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of 2738 Understanding Concerning the Technical Work of the 2739 Internet Assigned Numbers Authority", RFC 2860, June 2000. 2741 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 2742 Timestamps", RFC 3339, July 2002. 2744 [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 2745 Specifications: ABNF", RFC 4234, October 2005. 2747 [RFC4645] Ewell, D., Ed., "Initial Language Subtag Registry", 2748 September 2006, . 2750 [RFC4647] Phillips, A., Ed. and M. Davis, Ed., "Matching of Language 2751 Tags", September 2006, 2752 . 2754 [UN_M.49] Statistics Division, United Nations, "Standard Country or 2755 Area Codes for Statistical Use", UN Standard Country or 2756 Area Codes for Statistical Use, Revision 4 (United Nations 2757 publication, Sales No. 98.XVII.9, June 1999. 2759 9.2. Informative References 2761 [MARC21] Library of Congress, National Development and MARC 2762 Standards Office, "MARC 21 Specifications for Record 2763 Structure, Character Sets, and Exchange Media", 2764 January 2000, . 2766 [RFC1766] Alvestrand, H., "Tags for the Identification of 2767 Languages", RFC 1766, March 1995. 2769 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) 2770 Part Three: Message Header Extensions for Non-ASCII Text", 2771 RFC 2047, November 1996. 2773 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded 2774 Word Extensions: Character Sets, Languages, and 2775 Continuations", RFC 2231, November 1997. 2777 [RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 2778 10646", RFC 2781, February 2000. 2780 [RFC3066] Alvestrand, H., "Tags for the Identification of 2781 Languages", BCP 47, RFC 3066, January 2001. 2783 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 2784 Text on Security Considerations", BCP 72, RFC 3552, 2785 July 2003. 2787 [RFC4646] Phillips, A., Ed. and M. Davis, Ed., "Tags for the 2788 Identification of Languages", September 2006, 2789 . 2791 [Unicode] Unicode Consortium, "The Unicode Consortium. The Unicode 2792 Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. 2793 ISBN 0-321-49081-0)", January 2007. 2795 [XML10] Bray (et al), T., "Extensible Markup Language (XML) 1.0", 2796 02 2004. 2798 [iso639.prin] 2799 ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory 2800 Committee: Working principles for ISO 639 maintenance", 2801 March 2000, 2802 . 2805 [record-jar] 2806 Raymond, E., "The Art of Unix Programming", 2003, 2807 . 2809 [registry-update] 2810 Ewell, D., Ed., "Update to the Language Subtag Registry", 2811 September 2006, . 2814 Appendix A. Acknowledgements 2816 Any list of contributors is bound to be incomplete; please regard the 2817 following as only a selection from the group of people who have 2818 contributed to make this document what it is today. 2820 The contributors to RFC 4646, RFC 4647, RFC 3066, and RFC 1766, the 2821 precursors of this document, made enormous contributions directly or 2822 indirectly to this document and are generally responsible for the 2823 success of language tags. 2825 The following people contributed to this document: 2827 Stephane Bortzmeyer, Karen Broome, Peter Constable, John Cowan, 2828 Martin Duerst, Frank Ellerman, Doug Ewell, Deborah Garside, Marion 2829 Gunn, Kent Karlsson, Chris Newman, Randy Presuhn, Stephen Silver, and 2830 many, many others. 2832 Very special thanks must go to Harald Tveit Alvestrand, who 2833 originated RFCs 1766 and 3066, and without whom this document would 2834 not have been possible. 2836 Special thanks go to Michael Everson, who served as the Language Tag 2837 Reviewer for almost the entire RFC 1766/RFC 3066 period, as well as 2838 the Language Subtag Reviewer since the adoption of RFC 4646. 2840 Special thanks also to Doug Ewell, for his production of the first 2841 complete subtag registry, his work to support and maintain new 2842 registrations, and his careful editorship of both RFC 4645 and 2843 [registry-update]. 2845 Appendix B. Examples of Language Tags (Informative) 2847 Simple language subtag: 2849 de (German) 2851 fr (French) 2853 ja (Japanese) 2855 i-enochian (example of a grandfathered tag) 2857 Language subtag plus Script subtag: 2859 zh-Hant (Chinese written using the Traditional Chinese script) 2861 zh-Hans (Chinese written using the Simplified Chinese script) 2863 sr-Cyrl (Serbian written using the Cyrillic script) 2865 sr-Latn (Serbian written using the Latin script) 2867 Language-Script-Region: 2869 zh-Hans-CN (Chinese written using the Simplified script as used in 2870 mainland China) 2872 sr-Latn-RS (Serbian written using the Latin script as used in 2873 Serbia) 2875 Language-Variant: 2877 sl-rozaj (Resian dialect of Slovenian) 2879 sl-nedis (Nadiza dialect of Slovenian) 2881 Language-Region-Variant: 2883 de-CH-1901 (German as used in Switzerland using the 1901 variant 2884 [orthography]) 2886 sl-IT-nedis (Slovenian as used in Italy, Nadiza dialect) 2888 Language-Script-Region-Variant: 2890 hy-Latn-IT-arevela (Eastern Armenian written in Latin script, as 2891 used in Italy) 2893 Language-Region: 2895 de-DE (German for Germany) 2897 en-US (English as used in the United States) 2899 es-419 (Spanish appropriate for the Latin America and Caribbean 2900 region using the UN region code) 2902 Private use subtags: 2904 de-CH-x-phonebk 2906 az-Arab-x-AZE-derbend 2908 Extended language subtags: 2910 zh-cmn 2912 zh-cmn-Hant-CN 2914 Private use registry values: 2916 x-whatever (private use using the singleton 'x') 2918 qaa-Qaaa-QM-x-southern (all private tags) 2920 de-Qaaa (German, with a private script) 2922 sr-Latn-QM (Serbian, Latin-script, private region) 2924 sr-Qaaa-RS (Serbian, private script, for Serbia) 2926 Tags that use extensions (examples ONLY: extensions MUST be defined 2927 by revision or update to this document or by RFC): 2929 en-US-u-islamCal 2931 zh-CN-a-myExt-x-private 2933 en-a-myExt-b-another 2935 Some Invalid Tags: 2937 de-419-DE (two region tags) 2939 a-DE (use of a single-character subtag in primary position; note 2940 that there are a few grandfathered tags that start with "i-" that 2941 are valid) 2943 ar-a-aaa-b-bbb-a-ccc (two extensions with same single-letter 2944 prefix) 2946 Authors' Addresses 2948 Addison Phillips (editor) 2949 Yahoo! Inc. 2951 Email: addison@inter-locale.com 2952 URI: http://www.inter-locale.com 2954 Mark Davis (editor) 2955 Google 2957 Email: mark.davis@macchiato.com or mark.davis@google.com 2959 Full Copyright Statement 2961 Copyright (C) The IETF Trust (2007). 2963 This document is subject to the rights, licenses and restrictions 2964 contained in BCP 78, and except as set forth therein, the authors 2965 retain all their rights. 2967 This document and the information contained herein are provided on an 2968 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 2969 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 2970 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 2971 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 2972 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 2973 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 2975 Intellectual Property 2977 The IETF takes no position regarding the validity or scope of any 2978 Intellectual Property Rights or other rights that might be claimed to 2979 pertain to the implementation or use of the technology described in 2980 this document or the extent to which any license under such rights 2981 might or might not be available; nor does it represent that it has 2982 made any independent effort to identify any such rights. 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