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'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 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) Summary: 7 errors (**), 0 flaws (~~), 9 warnings (==), 15 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 Quest Software 4 Expires: February 16, 2006 M. Davis, Ed. 5 IBM 6 August 15, 2005 8 Tags for Identifying Languages 9 draft-ietf-ltru-registry-11 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on February 16, 2006. 36 Copyright Notice 38 Copyright (C) The Internet Society (2005). 40 Abstract 42 This document describes the structure, content, construction, and 43 semantics of language tags for use in cases where it is desirable to 44 indicate the language used in an information object. It also 45 describes how to register values for use in language tags and the 46 creation of user defined extensions for private interchange. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. The Language Tag . . . . . . . . . . . . . . . . . . . . . . . 4 52 2.1 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 4 53 2.2 Language Subtag Sources and Interpretation . . . . . . . . 6 54 2.2.1 Primary Language Subtag . . . . . . . . . . . . . . . 8 55 2.2.2 Extended Language Subtags . . . . . . . . . . . . . . 10 56 2.2.3 Script Subtag . . . . . . . . . . . . . . . . . . . . 10 57 2.2.4 Region Subtag . . . . . . . . . . . . . . . . . . . . 11 58 2.2.5 Variant Subtags . . . . . . . . . . . . . . . . . . . 13 59 2.2.6 Extension Subtags . . . . . . . . . . . . . . . . . . 14 60 2.2.7 Private Use Subtags . . . . . . . . . . . . . . . . . 15 61 2.2.8 Pre-Existing RFC 3066 Registrations . . . . . . . . . 16 62 2.2.9 Classes of Conformance . . . . . . . . . . . . . . . . 16 63 3. Registry Format and Maintenance . . . . . . . . . . . . . . . 18 64 3.1 Format of the IANA Language Subtag Registry . . . . . . . 18 65 3.2 Maintenance of the Registry . . . . . . . . . . . . . . . 23 66 3.3 Stability of IANA Registry Entries . . . . . . . . . . . . 24 67 3.4 Registration Procedure for Subtags . . . . . . . . . . . . 28 68 3.5 Possibilities for Registration . . . . . . . . . . . . . . 31 69 3.6 Extensions and Extensions Registry . . . . . . . . . . . . 33 70 3.7 Initialization of the Registries . . . . . . . . . . . . . 36 71 4. Formation and Processing of Language Tags . . . . . . . . . . 37 72 4.1 Choice of Language Tag . . . . . . . . . . . . . . . . . . 37 73 4.2 Meaning of the Language Tag . . . . . . . . . . . . . . . 39 74 4.3 Length Considerations . . . . . . . . . . . . . . . . . . 40 75 4.3.1 Working with Limited Buffer Sizes . . . . . . . . . . 40 76 4.3.2 Truncation of Language Tags . . . . . . . . . . . . . 42 77 4.4 Canonicalization of Language Tags . . . . . . . . . . . . 42 78 4.5 Considerations for Private Use Subtags . . . . . . . . . . 44 79 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 80 5.1 Language Subtag Registry . . . . . . . . . . . . . . . . . 46 81 5.2 Extensions Registry . . . . . . . . . . . . . . . . . . . 47 82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 48 83 7. Character Set Considerations . . . . . . . . . . . . . . . . . 49 84 8. Changes from RFC 3066 . . . . . . . . . . . . . . . . . . . . 50 85 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 53 86 9.1 Normative References . . . . . . . . . . . . . . . . . . . 53 87 9.2 Informative References . . . . . . . . . . . . . . . . . . 54 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 55 89 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 56 90 B. Examples of Language Tags (Informative) . . . . . . . . . . . 57 91 Intellectual Property and Copyright Statements . . . . . . . . 60 93 1. Introduction 95 Human beings on our planet have, past and present, used a number of 96 languages. There are many reasons why one would want to identify the 97 language used when presenting or requesting information. 99 User's language preferences often need to be identified so that 100 appropriate processing can be applied. For example, the user's 101 language preferences in a Web browser can be used to select Web pages 102 appropriately. Language preferences can also be used to select among 103 tools (such as dictionaries) to assist in the processing or 104 understanding of content in different languages. 106 In addition, knowledge about the particular language used by some 107 piece of information content might be useful or even required by some 108 types of processing; for example spell-checking, computer-synthesized 109 speech, Braille transcription, or high-quality print renderings. 111 One means of indicating the language used is by labeling the 112 information content with an identifier or "tag". These tags can be 113 used to specify user preferences when selecting information content, 114 or for labeling additional attributes of content and associated 115 resources. 117 Tags can also be used to indicate additional language attributes of 118 content. For example, indicating specific information about the 119 dialect, writing system, or orthography used in a document or 120 resource may enable the user to obtain information in a form that 121 they can understand, or important in processing or rendering the 122 given content into an appropriate form or style. 124 This document specifies a particular identifier mechanism (the 125 language tag) and a registration function for values to be used to 126 form tags. It also defines a mechanism for private use values and 127 future extension. 129 This document replaces [RFC3066], which replaced [RFC1766]. For a 130 list of changes in this document, see Section 8. 132 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 133 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 134 document are to be interpreted as described in [RFC2119]. 136 2. The Language Tag 138 Language tags are used to help identify languages, whether spoken, 139 written, signed, or otherwise signaled, for the purpose of 140 communication. This includes constructed and artificial languages, 141 but excludes languages not intended primarily for human 142 communication, such as programming languages. 144 2.1 Syntax 146 The language tag is composed of one or more parts or "subtags". Each 147 subtag consists of a sequence of alpha-numeric characters. Subtags 148 are distinguished and separated from one another by a hyphen ("-", 149 ABNF [RFC2234bis] %x2D). A language tag consists of a "primary 150 language" subtag and a (possibly empty) series of subsequent subtags, 151 each of which refines or narrows the range of language identified by 152 the overall tag. 154 Each type of subtag is distinguished by length, position in the tag, 155 and content: subtags can be recognized solely by these features. 156 This makes it possible to construct a parser that can extract and 157 assign some semantic information to the subtags, even if the specific 158 subtag values are not recognized. Thus a parser need not have an up- 159 to-date copy (or any copy at all) of the subtag registry to perform 160 most searching and matching operations. 162 The syntax of the language tag in ABNF [RFC2234bis] is: 164 Language-Tag = langtag 165 / privateuse ; private use tag 166 / grandfathered ; grandfathered registrations 168 langtag = (language 169 ["-" script] 170 ["-" region] 171 *("-" variant) 172 *("-" extension) 173 ["-" privateuse]) 175 language = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code 176 / 4ALPHA ; reserved for future use 177 / 5*8ALPHA ; registered language subtag 179 extlang = *3("-" 3ALPHA) ; reserved for future use 181 script = 4ALPHA ; ISO 15924 code 183 region = 2ALPHA ; ISO 3166 code 184 / 3DIGIT ; UN M.49 code 186 variant = 5*8alphanum ; registered variants 187 / (DIGIT 3alphanum) 189 extension = singleton 1*("-" (2*8alphanum)) 191 singleton = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT 192 ; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9" 193 ; Single letters: x/X is reserved for private use 195 privateuse = ("x"/"X") 1*("-" (1*8alphanum)) 197 grandfathered = 1*3ALPHA 1*2("-" (2*8alphanum)) 198 ; grandfathered registration 199 ; Note: i is the only singleton 200 ; that starts a grandfathered tag 202 alphanum = (ALPHA / DIGIT) ; letters and numbers 204 Figure 1: Language Tag ABNF 206 Note: There is a subtlety in the ABNF for 'variant': variants 207 starting with a digit MAY be four characters long, while those 208 starting with a letter MUST be at least five characters long. 210 All subtags have a maximum length of eight characters and whitespace 211 is not permitted in a language tag. For examples of language tags, 212 see Appendix B. 214 Note that although [RFC2234bis] refers to octets, the language tags 215 described in this document are sequences of characters from the US- 216 ASCII [ISO646] repertoire. Language tags MAY be used in documents 217 and applications that use other encodings, so long as these encompass 218 the US-ASCII repertoire. An example of this would be an XML document 219 that uses the UTF-16LE [RFC2781] encoding of [Unicode]. 221 The tags and their subtags, including private use and extensions, are 222 to be treated as case insensitive: there exist conventions for the 223 capitalization of some of the subtags, but these MUST NOT be taken to 224 carry meaning. 226 For example: 228 o [ISO639-1] recommends that language codes be written in lower case 229 ('mn' Mongolian). 231 o [ISO3166-1] recommends that country codes be capitalized ('MN' 232 Mongolia). 234 o [ISO15924] recommends that script codes use lower case with the 235 initial letter capitalized ('Cyrl' Cyrillic). 237 However, in the tags defined by this document, the uppercase US-ASCII 238 letters in the range 'A' through 'Z' are considered equivalent and 239 mapped directly to their US-ASCII lowercase equivalents in the range 240 'a' through 'z'. Thus the tag "mn-Cyrl-MN" is not distinct from "MN- 241 cYRL-mn" or "mN-cYrL-Mn" (or any other combination) and each of these 242 variations conveys the same meaning: Mongolian written in the 243 Cyrillic script as used in Mongolia. 245 2.2 Language Subtag Sources and Interpretation 247 The namespace of language tags and their subtags is administered by 248 the Internet Assigned Numbers Authority (IANA) [RFC2860] according to 249 the rules in Section 5 of this document. The Language Subtag 250 Registry maintained by IANA is the source for valid subtags: other 251 standards referenced in this section provide the source material for 252 that registry. 254 Terminology in this section: 256 o Tag or tags refers to a complete language tag, such as 257 "fr-Latn-CA". Examples of tags in this document are enclosed in 258 double-quotes ("en-US"). 260 o Subtag refers to a specific section of a tag, delimited by hyphen, 261 such as the subtag 'Latn' in "fr-Latn-CA". Examples of subtags in 262 this document are enclosed in single quotes ('Latn'). 264 o Code or codes refers to values defined in external standards (and 265 which are used as subtags in this document). For example, 'Latn' 266 is an [ISO15924] script code which was used to define the 'Latn' 267 script subtag for use in a language tag. Examples of codes in 268 this document are enclosed in single quotes ('en', 'Latn'). 270 The definitions in this section apply to the various subtags within 271 the language tags defined by this document, excepting those 272 "grandfathered" tags defined in Section 2.2.8. 274 Language tags are designed so that each subtag type has unique length 275 and content restrictions. These make identification of the subtag's 276 type possible, even if the content of the subtag itself is 277 unrecognized. This allows tags to be parsed and processed without 278 reference to the latest version of the underlying standards or the 279 IANA registry and makes the associated exception handling when 280 parsing tags simpler. 282 Subtags in the IANA registry that do not come from an underlying 283 standard can only appear in specific positions in a tag. 284 Specifically, they can only occur as primary language subtags or as 285 variant subtags. 287 Note that sequences of private use and extension subtags MUST occur 288 at the end of the sequence of subtags and MUST NOT be interspersed 289 with subtags defined elsewhere in this document. 291 Single letter and digit subtags are reserved for current or future 292 use. These include the following current uses: 294 o The single letter subtag 'x' is reserved to introduce a sequence 295 of private use subtags. The interpretation of any private use 296 subtags is defined solely by private agreement and is not defined 297 by the rules in this section or in any standard or registry 298 defined in this document. 300 o All other single letter subtags are reserved to introduce 301 standardized extension subtag sequences as described in 302 Section 3.6. 304 The single letter subtag 'i' is used by some grandfathered tags, such 305 as "i-enochian", where it always appears in the first position and 306 cannot be confused with an extension. 308 2.2.1 Primary Language Subtag 310 The primary language subtag is the first subtag in a language tag 311 (with the exception of private use and certain grandfathered tags) 312 and cannot be omitted. The following rules apply to the primary 313 language subtag: 315 1. All two character language subtags were defined in the IANA 316 registry according to the assignments found in the standard ISO 317 639 Part 1, "ISO 639-1:2002, Codes for the representation of 318 names of languages -- Part 1: Alpha-2 code" [ISO639-1], or using 319 assignments subsequently made by the ISO 639 Part 1 maintenance 320 agency or governing standardization bodies. 322 2. All three character language subtags were defined in the IANA 323 registry according to the assignments found in ISO 639 Part 2, 324 "ISO 639-2:1998 - Codes for the representation of names of 325 languages -- Part 2: Alpha-3 code - edition 1" [ISO639-2], or 326 assignments subsequently made by the ISO 639 Part 2 maintenance 327 agency or governing standardization bodies. 329 3. The subtags in the range 'qaa' through 'qtz' are reserved for 330 private use in language tags. These subtags correspond to codes 331 reserved by ISO 639-2 for private use. These codes MAY be used 332 for non-registered primary-language subtags (instead of using 333 private use subtags following 'x-'). Please refer to Section 4.5 334 for more information on private use subtags. 336 4. All four character language subtags are reserved for possible 337 future standardization. 339 5. All language subtags of 5 to 8 characters in length in the IANA 340 registry were defined via the registration process in Section 3.4 341 and MAY be used to form the primary language subtag. At the time 342 this document was created, there were no examples of this kind of 343 subtag and future registrations of this type will be discouraged: 344 primary languages are strongly RECOMMENDED for registration with 345 ISO 639 and proposals rejected by ISO 639/RA will be closely 346 scrutinized before they are registered with IANA. 348 6. The single character subtag 'x' as the primary subtag indicates 349 that the language tag consists solely of subtags whose meaning is 350 defined by private agreement. For example, in the tag "x-fr-CH", 351 the subtags 'fr' and 'CH' SHOULD NOT be taken to represent the 352 French language or the country of Switzerland (or any other value 353 in the IANA registry) unless there is a private agreement in 354 place to do so. See Section 4.5. 356 7. The single character subtag 'i' is used by some grandfathered 357 tags (see Section 2.2.8) such as "i-klingon" and "i-bnn". (Other 358 grandfathered tags have a primary language subtag in their first 359 position) 361 8. Other values MUST NOT be assigned to the primary subtag except by 362 revision or update of this document. 364 Note: For languages that have both an ISO 639-1 two character code 365 and an ISO 639-2 three character code, only the ISO 639-1 two 366 character code is defined in the IANA registry. 368 Note: For languages that have no ISO 639-1 two character code and for 369 which the ISO 639-2/T (Terminology) code and the ISO 639-2/B 370 (Bibliographic) codes differ, only the Terminology code is defined in 371 the IANA registry. At the time this document was created, all 372 languages that had both kinds of three character code were also 373 assigned a two character code; it is not expected that future 374 assignments of this nature will occur. 376 Note: To avoid problems with versioning and subtag choice as 377 experienced during the transition between RFC 1766 and RFC 3066, as 378 well as the canonical nature of subtags defined by this document, the 379 ISO 639 Registration Authority Joint Advisory Committee (ISO 639/ 380 RA-JAC) has included the following statement in [iso639.principles]: 382 "A language code already in ISO 639-2 at the point of freezing ISO 383 639-1 shall not later be added to ISO 639-1. This is to ensure 384 consistency in usage over time, since users are directed in Internet 385 applications to employ the alpha-3 code when an alpha-2 code for that 386 language is not available." 388 In order to avoid instability in the canonical form of tags, if a two 389 character code is added to ISO 639-1 for a language for which a three 390 character code was already included in ISO 639-2, the two character 391 code MUST NOT be registered. See Section 3.3. 393 For example, if some content were tagged with 'haw' (Hawaiian), which 394 currently has no two character code, the tag would not be invalidated 395 if ISO 639-1 were to assign a two character code to the Hawaiian 396 language at a later date. 398 For example, one of the grandfathered IANA registrations is 399 "i-enochian". The subtag 'enochian' could be registered in the IANA 400 registry as a primary language subtag (assuming that ISO 639 does not 401 register this language first), making tags such as "enochian-AQ" and 402 "enochian-Latn" valid. 404 2.2.2 Extended Language Subtags 406 The following rules apply to the extended language subtags: 408 1. Three letter subtags immediately following the primary subtag are 409 reserved for future standardization, anticipating work that is 410 currently under way on ISO 639. 412 2. Extended language subtags MUST follow the primary subtag and 413 precede any other subtags. 415 3. There MAY be up to three extended language subtags. 417 4. Extended language subtags MUST NOT be registered or used to form 418 language tags. Their syntax is described here so that 419 implementations can be compatible with any future revision of 420 this document which does provide for their registration. 422 Extended language subtag records, once they appear in the registry, 423 MUST include exactly one 'Prefix' field indicating an appropriate 424 language subtag or sequence of subtags that MUST always appear as a 425 prefix to the extended language subtag. 427 Example: In a future revision or update of this document, the tag 428 "zh-gan" (registered under RFC 3066) might become a valid non- 429 grandfathered (that is, redundant) tag in which the subtag 'gan' 430 might represent the Chinese dialect 'Gan'. 432 2.2.3 Script Subtag 434 Script subtags are used to indicate the script or writing system 435 variations that distinguish the written forms of a language or its 436 dialects. The following rules apply to the script subtags: 438 1. All four character subtags were defined according to 439 [ISO15924]--"Codes for the representation of the names of 440 scripts": alpha-4 script codes, or subsequently assigned by the 441 ISO 15924 maintenance agency or governing standardization bodies, 442 denoting the script or writing system used in conjunction with 443 this language. 445 2. Script subtags MUST immediately follow the primary language 446 subtag and all extended language subtags and MUST occur before 447 any other type of subtag described below. 449 3. The script subtags 'Qaaa' through 'Qabx' are reserved for private 450 use in language tags. These subtags correspond to codes reserved 451 by ISO 15924 for private use. These codes MAY be used for non- 452 registered script values. Please refer to Section 4.5 for more 453 information on private use subtags. 455 4. Script subtags MUST NOT be registered using the process in 456 Section 3.4 of this document. Variant subtags MAY be considered 457 for registration for that purpose. 459 5. There MUST be at most one script subtag in a language tag and the 460 script subtag SHOULD be omitted when it adds no distinguishing 461 value to the tag or when the primary language subtag's record 462 includes a Suppress-Script field listing the applicable script 463 subtag. 465 Example: "sr-Latn" represents Serbian written using the Latin script. 467 2.2.4 Region Subtag 469 Region subtags are used to indicate linguistic variations associated 470 with or appropriate to a specific country, territory, or region. 471 Typically, a region subtag is used to indicate regional dialects or 472 usage, or region-specific spelling conventions. A region subtag can 473 also be used to indicate that content is expressed in a way that is 474 appropriate for use throughout a region; for instance, Spanish 475 content tailored to be useful throughout Latin America. 477 The following rules apply to the region subtags: 479 1. Region subtags MUST follow any language, extended language, or 480 script subtags and MUST precede all other subtags. 482 2. All two character subtags following the primary subtag were 483 defined in the IANA registry according to the assignments found 484 in [ISO3166-1] ("Codes for the representation of names of 485 countries and their subdivisions -- Part 1: Country codes") using 486 the list of alpha-2 country codes, or using assignments 487 subsequently made by the ISO 3166 maintenance agency or governing 488 standardization bodies. 490 3. All three character subtags consisting of digit (numeric) 491 characters following the primary subtag were defined in the IANA 492 registry according to the assignments found in UN Standard 493 Country or Area Codes for Statistical Use [UN_M.49] or 494 assignments subsequently made by the governing standards body. 495 Note that not all of the UN M.49 codes are defined in the IANA 496 registry. The following rules define which codes are entered 497 into the registry as valid subtags: 499 A. UN numeric codes assigned to 'macro-geographical 500 (continental)' or sub-regions MUST be registered in the 501 registry. These codes are not associated with an assigned 502 ISO 3166 alpha-2 code and represent supra-national areas, 503 usually covering more than one nation, state, province, or 504 territory. 506 B. UN numeric codes for 'economic groupings' or 'other 507 groupings' MUST NOT be registered in the IANA registry and 508 MUST NOT be used to form language tags. 510 C. UN numeric codes for countries or areas with ambiguous ISO 511 3166 alpha-2 codes, when entered into the registry, MUST be 512 defined according to the rules in Section 3.3 and MUST be 513 used to form language tags that represent the country or 514 region for which they are defined. 516 D. UN numeric codes for countries or areas for which there is an 517 associated ISO 3166 alpha-2 code in the registry MUST NOT be 518 entered into the registry and MUST NOT be used to form 519 language tags. Note that the ISO 3166-based subtag in the 520 registry MUST actually be associated with the UN M.49 code in 521 question. 523 E. UN numeric codes and ISO 3166 alpha-2 codes for countries or 524 areas listed as eligible for registration in [initial- 525 registry] but not presently registered MAY be entered into 526 the IANA registry via the process described in Section 3.4. 527 Once registered, these codes MAY be used to form language 528 tags. 530 F. All other UN numeric codes for countries or areas which do 531 not have an associated ISO 3166 alpha-2 code MUST NOT be 532 entered into the registry and MUST NOT be used to form 533 language tags. For more information about these codes, see 534 Section 3.3. 536 4. Note: The alphanumeric codes in Appendix X of the UN document 537 MUST NOT be entered into the registry and MUST NOT be used to 538 form language tags. (At the time this document was created these 539 values match the ISO 3166 alpha-2 codes.) 541 5. There MUST be at most one region subtag in a language tag and the 542 region subtag MAY be omitted, as when it adds no distinguishing 543 value to the tag. 545 6. The region subtags 'AA', 'QM'-'QZ', 'XA'-'XZ', and 'ZZ' are 546 reserved for private use in language tags. These subtags 547 correspond to codes reserved by ISO 3166 for private use. These 548 codes MAY be used for private use region subtags (instead of 549 using a private use subtag sequence). Please refer to 550 Section 4.5 for more information on private use subtags. 552 "de-CH" represents German ('de') as used in Switzerland ('CH'). 554 "sr-Latn-CS" represents Serbian ('sr') written using Latin script 555 ('Latn') as used in Serbia and Montenegro ('CS'). 557 "es-419" represents Spanish ('es') appropriate to the UN-defined 558 Latin America and Caribbean region ('419'). 560 2.2.5 Variant Subtags 562 Variant subtags are used to indicate additional, well-recognized 563 variations that define a language or its dialects which are not 564 covered by other available subtags. The following rules apply to the 565 variant subtags: 567 1. Variant subtags are not associated with any external standard. 568 Variant subtags and their meanings are defined by the 569 registration process defined in Section 3.4. 571 2. Variant subtags MUST follow all of the other defined subtags, but 572 precede any extension or private use subtag sequences. 574 3. More than one variant MAY be used to form the language tag. 576 4. Variant subtags MUST be registered with IANA according to the 577 rules in Section 3.4 of this document before being used to form 578 language tags. In order to distinguish variants from other types 579 of subtags, registrations MUST meet the following length and 580 content restrictions: 582 1. Variant subtags that begin with a letter (a-z, A-Z) MUST be 583 at least five characters long. 585 2. Variant subtags that begin with a digit (0-9) MUST be at 586 least four characters long. 588 Variant subtag records in the language subtag registry MAY include 589 one or more 'Prefix' fields, which indicates the language tag or tags 590 that would make a suitable prefix (with other subtags, as 591 appropriate) in forming a language tag with the variant. For 592 example, the subtag 'nedis' has a Prefix of "sl", making it suitable 593 to form language tags such as "sl-nedis" and "sl-IT-nedis", but not 594 suitable for use in a tag such as "zh-nedis" or "it-IT-nedis". 596 "sl-nedis" represents the Natisone or Nadiza dialect of Slovenian. 598 "de-CH-1996" represents German as used in Switzerland and as written 599 using the spelling reform beginning in the year 1996 C.E. 601 Most variants that share a prefix are mutually exclusive. For 602 example, the German orthographic variations '1996' and '1901' SHOULD 603 NOT be used in the same tag, as they represent the dates of different 604 spelling reforms. A variant that can meaningfully be used in 605 combination with another variant SHOULD include a 'Prefix' field in 606 its registry record that lists that other variant. For example, if 607 another German variant 'example' were created that made sense to use 608 with '1996', then 'example' should include two Prefix fields: "de" 609 and "de-1996". 611 2.2.6 Extension Subtags 613 Extensions provide a mechanism for extending language tags for use in 614 various applications. See: Section 3.6. The following rules apply 615 to extensions: 617 1. Extension subtags are separated from the other subtags defined 618 in this document by a single character subtag ("singleton"). 619 The singleton MUST be one allocated to a registration authority 620 via the mechanism described in Section 3.6 and MUST NOT be the 621 letter 'x', which is reserved for private use subtag sequences. 623 2. Note: Private use subtag sequences starting with the singleton 624 subtag 'x' are described below. 626 3. An extension MUST follow at least a primary language subtag. 627 That is, a language tag cannot begin with an extension. 628 Extensions extend language tags, they do not override or replace 629 them. For example, "a-value" is not a well-formed language tag, 630 while "de-a-value" is. 632 4. Each singleton subtag MUST appear at most one time in each tag 633 (other than as a private use subtag). That is, singleton 634 subtags MUST NOT be repeated. For example, the tag "en-a-bbb-a- 635 ccc" is invalid because the subtag 'a' appears twice. Note that 636 the tag "en-a-bbb-x-a-ccc" is valid because the second 637 appearance of the singleton 'a' is in a private use sequence. 639 5. Extension subtags MUST meet all of the requirements for the 640 content and format of subtags defined in this document. 642 6. Extension subtags MUST meet whatever requirements are set by the 643 document that defines their singleton prefix and whatever 644 requirements are provided by the maintaining authority. 646 7. Each extension subtag MUST be from two to eight characters long 647 and consist solely of letters or digits, with each subtag 648 separated by a single '-'. 650 8. Each singleton MUST be followed by at least one extension 651 subtag. For example, the tag "tlh-a-b-foo" is invalid because 652 the first singleton 'a' is followed immediately by another 653 singleton 'b'. 655 9. Extension subtags MUST follow all language, extended language, 656 script, region and variant subtags in a tag. 658 10. All subtags following the singleton and before another singleton 659 are part of the extension. Example: In the tag "fr-a-Latn", the 660 subtag 'Latn' does not represent the script subtag 'Latn' 661 defined in the IANA Language Subtag Registry. Its meaning is 662 defined by the extension 'a'. 664 11. In the event that more than one extension appears in a single 665 tag, the tag SHOULD be canonicalized as described in 666 Section 4.4. 668 For example, if the prefix singleton 'r' and the shown subtags were 669 defined, then the following tag would be a valid example: "en-Latn- 670 GB-boont-r-extended-sequence-x-private" 672 2.2.7 Private Use Subtags 674 Private use subtags are used to indicate distinctions in language 675 important in a given context by private agreement. The following 676 rules apply to private use subtags: 678 1. Private use subtags are separated from the other subtags defined 679 in this document by the reserved single-character subtag 'x'. 681 2. Private use subtags MUST conform to the format and content 682 constraints defined in the ABNF for all subtags. 684 3. Private use subtags MUST follow all language, extended language, 685 script, region, variant, and extension subtags in the tag. 686 Another way of saying this is that all subtags following the 687 singleton 'x' MUST be considered private use. Example: The 688 subtag 'US' in the tag "en-x-US" is a private use subtag. 690 4. A tag MAY consist entirely of private use subtags. 692 5. No source is defined for private use subtags. Use of private use 693 subtags is by private agreement only. 695 6. Private use subtags are NOT RECOMMENDED where alternatives exist 696 or for general interchange. See Section 4.5 for more information 697 on private use subtag choice. 699 For example: Users who wished to utilize codes from the Ethnologue 700 publication of SIL International for language identification might 701 agree to exchange tags such as "az-Arab-x-AZE-derbend". This example 702 contains two private use subtags. The first is 'AZE' and the second 703 is 'derbend'. 705 2.2.8 Pre-Existing RFC 3066 Registrations 707 Existing IANA-registered language tags from RFC 1766 and/or RFC 3066 708 maintain their validity. These tags will be maintained in the 709 registry in records of either the "grandfathered" or "redundant" 710 type. For more information see Section 3.7. 712 It is important to note that all language tags formed under the 713 guidelines in this document were either legal, well-formed tags or 714 could have been registered under RFC 3066. 716 2.2.9 Classes of Conformance 718 Implementations sometimes need to describe their capabilities with 719 regard to the rules and practices described in this document. There 720 are two classes of conforming implementations described by this 721 document: "well-formed" processors and "validating" processors. 722 Claims of conformance SHOULD explicitly reference one of these 723 definitions. 725 An implementation that claims to check for well-formed language tags 726 MUST: 728 o Check that the tag and all of its subtags, including extension and 729 private use subtags, conform to the ABNF or that the tag is on the 730 list of grandfathered tags. 732 o Check that singleton subtags that identify extensions do not 733 repeat. For example, the tag "en-a-xx-b-yy-a-zz" is not well- 734 formed. 736 Well-formed processors are strongly encouraged to implement the 737 canonicalization rules contained in Section 4.4. 739 An implementation that claims to be validating MUST: 741 o Check that the tag is well-formed. 743 o Specify the particular registry date for which the implementation 744 performs validation of subtags. 746 o Check that either the tag is a grandfathered tag, or that all 747 language, script, region, and variant subtags consist of valid 748 codes for use in language tags according to the IANA registry as 749 of the particular date specified by the implementation. 751 o Specify which, if any, extension RFCs as defined in Section 3.6 752 are supported, including version, revision, and date. 754 o For any such extensions supported, check that all subtags used in 755 that extension are valid. 757 o For variant and extended language subtags, if the registry 758 contains one or more 'Prefix' fields for that subtag, check that 759 the tag matches at least one prefix. The tag matches if all the 760 subtags in the 'Prefix' also appear in the tag. For example, the 761 prefix "es-CO" matches the tag "es-Latn-CO-x-private" because both 762 the 'es' language subtag and 'CO' region subtag appear in the tag. 764 3. Registry Format and Maintenance 766 This section defines the Language Subtag Registry and the maintenance 767 and update procedures associated with it, as well as a registry for 768 extensions to language tags (Section 3.6). 770 The Language Subtag Registry contains a comprehensive list of all of 771 the subtags valid in language tags. This allows implementers a 772 straightforward and reliable way to validate language tags. The 773 Language Subtag Registry will be maintained so that, except for 774 extension subtags, it is possible to validate all of the subtags that 775 appear in a language tag under the provisions of this document or its 776 revisions or successors. In addition, the meaning of the various 777 subtags will be unambiguous and stable over time. (The meaning of 778 private use subtags, of course, is not defined by the IANA registry.) 780 3.1 Format of the IANA Language Subtag Registry 782 The IANA Language Subtag Registry ("the registry") consists of a text 783 file that is machine readable in the format described in this 784 section, plus copies of the registration forms approved by the 785 Language Subtag Reviewer in accordance with the process described in 786 Section 3.4. With the exception of the registration forms for 787 grandfathered and redundant tags, no registration records will be 788 maintained for the initial set of subtags. 790 The registry is in a modified record-jar format text file [record- 791 jar]. Lines are limited to 72 characters, including all whitespace. 793 Records are separated by lines containing only the sequence "%%" 794 (%x25.25). 796 Each field can be viewed as a single, logical line of ASCII 797 characters, comprising a field-name and a field-body separated by a 798 COLON character (%x3A). For convenience, the field-body portion of 799 this conceptual entity can be split into a multiple-line 800 representation; this is called "folding". The format of the registry 801 is described by the following ABNF (per [RFC2234bis]): 803 registry = record *("%%" CRLF record) 804 record = 1*( field-name *SP ":" *SP field-body CRLF ) 805 field-name = (ALPHA / DIGIT)[*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)] 806 field-body = *(ASCCHAR/LWSP) 807 ASCCHAR = %x21-25 / %x27-7E / UNICHAR ; Note: AMPERSAND is %x26 808 UNICHAR = "&#x" 2*6HEXDIG ";" 810 The sequence '..' (%x2E.2E) in a field-body denotes a range of 811 values. Such a range represents all subtags of the same length that 812 are alphabetically within that range, including the values explicitly 813 mentioned. For example 'a..c' denotes the values 'a', 'b', and 'c'. 815 Characters from outside the US-ASCII[ISO646] repertoire, as well as 816 the AMPERSAND character ("&", %x26) when it occurs in a field-body 817 are represented by a "Numeric Character Reference" using hexadecimal 818 notation in the style used by [XML10] (see 819 ). This consists of the 820 sequence "&#x" (%x26.23.78) followed by a hexadecimal representation 821 of the character's code point in [ISO10646] followed by a closing 822 semicolon (%x3B). For example, the EURO SIGN, U+20AC, would be 823 represented by the sequence "€". Note that the hexadecimal 824 notation MAY have between two and six digits. 826 All fields whose field-body contains a date value use the "full-date" 827 format specified in [RFC3339]. For example: "2004-06-28" represents 828 June 28, 2004 in the Gregorian calendar. 830 The first record in the file contains the single field whose field- 831 name is "File-Date". The field-body of this record contains the last 832 modification date of this copy of the registry, making it possible to 833 compare different versions of the registry. The registry on the IANA 834 website is the most current. Versions with an older date than that 835 one are not up-to-date. 837 File-Date: 2004-06-28 838 %% 840 Subsequent records represent subtags in the registry. Each of the 841 fields in each record MUST occur no more than once, unless otherwise 842 noted below. Each record MUST contain the following fields: 844 o 'Type' 846 * Type's field-value MUST consist of one of the following 847 strings: "language", "extlang", "script", "region", "variant", 848 "grandfathered", and "redundant" and denotes the type of tag or 849 subtag. 851 o Either 'Subtag' or 'Tag' 853 * Subtag's field-value contains the subtag being defined. This 854 field MUST only appear in records of whose 'Type' has one of 855 these values: "language", "extlang", "script", "region", or 856 "variant". 858 * Tag's field-value contains a complete language tag. This field 859 MUST only appear in records whose 'Type' has one of these 860 values: "grandfathered" or "redundant". 862 o Description 864 * Description's field-value contains a non-normative description 865 of the subtag or tag. 867 o Added 869 * Added's field-value contains the date the record was added to 870 the registry. 872 The 'Subtag' or 'Tag' field MUST use lowercase letters to form the 873 subtag or tag, with two exceptions. Subtags whose 'Type' field is 874 'script' (in other words, subtags defined by ISO 15924) MUST use 875 titlecase. Subtags whose 'Type' field is 'region' (in other words, 876 subtags defined by ISO 3166) MUST use uppercase. These exceptions 877 mirror the use of case in the underlying standards. 879 The field 'Description' MAY appear more than one time. At least one 880 of the 'Description' fields MUST contain a description of the tag 881 being registered written or transcribed into the Latin script; the 882 same or additional fields MAY also include a description in a non- 883 Latin script. The 'Description' field is used for identification 884 purposes and SHOULD NOT be taken to represent the actual native name 885 of the language or variation or to be in any particular language. 886 Most descriptions are taken directly from source standards such as 887 ISO 639 or ISO 3166. 889 Note: Descriptions in registry entries that correspond to ISO 639, 890 ISO 15924, ISO 3166 or UN M.49 codes are intended only to indicate 891 the meaning of that identifier as defined in the source standard at 892 the time it was added to the registry. The description does not 893 replace the content of the source standard itself. The descriptions 894 are not intended to be the English localized names for the subtags. 895 Localization or translation of language tag and subtag descriptions 896 is out of scope of this document. 898 Each record MAY also contain the following fields: 900 o Preferred-Value 902 * For fields of type 'language', 'extlang', 'script', 'region', 903 and 'variant', 'Preferred-Value' contains a subtag of the same 904 'Type' which is preferred for forming the language tag. 906 * For fields of type 'grandfathered' and 'redundant', a canonical 907 mapping to a complete language tag. 909 o Deprecated 911 * Deprecated's field-value contains the date the record was 912 deprecated. 914 o Prefix 916 * Prefix's field-value contains a language tag with which this 917 subtag MAY be used to form a new language tag, perhaps with 918 other subtags as well. This field MUST only appear in records 919 whose 'Type' field-value is 'variant' or 'extlang'. For 920 example, the 'Prefix' for the variant 'nedis' is 'sl', meaning 921 that the tags "sl-nedis" and "sl-IT-nedis" might be appropriate 922 while the tag "is-nedis" is not. 924 o Comments 926 * Comments contains additional information about the subtag, as 927 deemed appropriate for understanding the registry and 928 implementing language tags using the subtag or tag. 930 o Suppress-Script 932 * Suppress-Script contains a script subtag that SHOULD NOT be 933 used to form language tags with the associated primary language 934 subtag. This field MUST only appear in records whose 'Type' 935 field-value is 'language'. See Section 4.1. 937 The field 'Deprecated' MAY be added to any record via the maintenance 938 process described in Section 3.2 or via the registration process 939 described in Section 3.4. Usually the addition of a 'Deprecated' 940 field is due to the action of one of the standards bodies, such as 941 ISO 3166, withdrawing a code. In some historical cases it might not 942 have been possible to reconstruct the original deprecation date. For 943 these cases, an approximate date appears in the registry. Although 944 valid in language tags, subtags and tags with a 'Deprecated' field 945 are deprecated and validating processors SHOULD NOT generate these 946 subtags. Note that a record that contains a 'Deprecated' field and 947 no corresponding 'Preferred-Value' field has no replacement mapping. 949 The field 'Preferred-Value' contains a mapping between the record in 950 which it appears and a tag or subtag which SHOULD be preferred when 951 selected language tags. These values form three groups: 953 ISO 639 language codes which were later withdrawn in favor of 954 other codes. These values are mostly a historical curiosity. 956 ISO 3166 region codes which have been withdrawn in favor of a new 957 code. This sometimes happens when a country changes its name or 958 administration in such a way that warrants a new region code. 960 Tags grandfathered from RFC 3066. In many cases these tags have 961 become obsolete because the values they represent were later 962 encoded by ISO 639. 964 Records that contain a 'Preferred-Value' field MUST also have a 965 'Deprecated' field. This field contains a date of deprecation. Thus 966 a language tag processor can use the registry to construct the valid, 967 non-deprecated set of subtags for a given date. In addition, for any 968 given tag, a processor can construct the set of valid language tags 969 that correspond to that tag for all dates up to the date of the 970 registry. The ability to do these mappings MAY be beneficial to 971 applications that are matching, selecting, for filtering content 972 based on its language tags. 974 Note that 'Preferred-Value' mappings in records of type 'region' 975 sometimes do not represent exactly the same meaning as the original 976 value. There are many reasons for a country code to be changed and 977 the effect this has on the formation of language tags will depend on 978 the nature of the change in question. 980 In particular, the 'Preferred-Value' field does not imply retagging 981 content that uses the affected subtag. 983 The field 'Preferred-Value' MUST NOT be modified once created in the 984 registry. The field MAY be added to records of type "grandfathered" 985 and "region" according to the rules in Section 3.2. Otherwise the 986 field MUST NOT be added to any record already in the registry. 988 The 'Preferred-Value' field in records of type "grandfathered" and 989 "redundant" contains whole language tags that are strongly 990 RECOMMENDED for use in place of the record's value. In many cases 991 the mappings were created by deprecation of the tags during the 992 period before this document was adopted. For example, the tag "no- 993 nyn" was deprecated in favor of the ISO 639-1 defined language code 994 'nn'. 996 Records of type 'variant' MAY have more than one field of type 997 'Prefix'. Additional fields of this type MAY be added to a 'variant' 998 record via the registration process. 1000 Records of type 'extlang' MUST have _exactly_ one 'Prefix' field. 1002 The field-value of the 'Prefix' field consists of a language tag 1003 whose subtags are appropriate to use with this subtag. For example, 1004 the variant subtag '1996' has a Prefix field of "de". This means 1005 that tags starting with the sequence "de-" are appropriate with this 1006 subtag, so "de-Latg-1996" and "de-CH-1996" are both acceptable, while 1007 the tag "fr-1996" is an inappropriate choice. 1009 The field of type 'Prefix' MUST NOT be removed from any record. The 1010 field-value for this type of field MUST NOT be modified. 1012 The field 'Comments' MAY appear more than once per record. This 1013 field MAY be inserted or changed via the registration process and no 1014 guarantee of stability is provided. The content of this field is not 1015 restricted, except by the need to register the information, the 1016 suitability of the request, and by reasonable practical size 1017 limitations. Long texts about a particular subtag are frowned upon. 1019 The field 'Suppress-Script' MUST only appear in records whose 'Type' 1020 field-value is 'language'. This field MUST NOT appear more than one 1021 time in a record. This field indicates a script used to write the 1022 overwhelming majority of documents for the given language and which 1023 therefore adds no distinguishing information to a language tag. It 1024 helps ensure greater compatibility between the language tags 1025 generated according to the rules in this document and language tags 1026 and tag processors or consumers based on RFC 3066. For example, 1027 virtually all Icelandic documents are written in the Latin script, 1028 making the subtag 'Latn' redundant in the tag "is-Latn". 1030 3.2 Maintenance of the Registry 1032 Maintenance of the registry requires that as codes are assigned or 1033 withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language 1034 Subtag Reviewer MUST evaluate each change, determine whether it 1035 conflicts with existing registry entries, and submit the information 1036 to IANA for inclusion in the registry. If an change takes place and 1037 the Language Subtag Reviewer does not do this in a timely manner, 1038 then any interested party MAY use the procedure in Section 3.4 to 1039 register the appropriate update. 1041 Note: The redundant and grandfathered entries together are the 1042 complete list of tags registered under [RFC3066]. The redundant tags 1043 are those that can now be formed using the subtags defined in the 1044 registry together with the rules of Section 2.2. The grandfathered 1045 entries are those that can never be legal under those same 1046 provisions. 1048 The set of redundant and grandfathered tags is permanent and stable: 1049 new entries in this section MUST NOT be added and existing entries 1050 MUST NOT be removed. Records of type 'grandfathered' MAY have their 1051 type converted to 'redundant': see Section 3.7 for more information. 1053 RFC 3066 tags that were deprecated prior to the adoption of this 1054 document are part of the list of grandfathered tags and their 1055 component subtags were not included as registered variants (although 1056 they remain eligible for registration). For example, the tag "art- 1057 lojban" was deprecated in favor of the language subtag 'jbo'. 1059 The Language Subtag Reviewer MUST ensure that new subtags meet the 1060 requirements in Section 4.1 or submit an appropriate alternate subtag 1061 as described in that section. When either a change or addition to 1062 the registry is needed, the Language Subtag Reviewer MUST prepare the 1063 complete record, including all fields, and forward it to IANA for 1064 insertion into the registry. 1066 If record represents a new subtag that does not currently exist in 1067 the registry, then the message's subject line MUST include the word 1068 "INSERT". If the record represents a change to an existing subtag, 1069 then the subject line of the message MUST include the word "MODIFY". 1070 The message MUST contain both the record for the subtag being 1071 inserted or modified and the new File-Date record. Here is an 1072 example of what the body of the message might contain: 1074 LANGUAGE SUBTAG MODIFICATION 1075 File-Date: 2005-01-02 1076 %% 1077 Type: variant 1078 Subtag: nedis 1079 Description: Natisone dialect 1080 Description: Nadiza dialect 1081 Added: 2003-10-09 1082 Prefix: sl 1083 Comments: This is a comment shown 1084 as an example. 1085 %% 1087 Figure 4 1089 Whenever an entry is created or modified in the registry, the 'File- 1090 Date' record at the start of the registry is updated to reflect the 1091 most recent modification date in the [RFC3339] "full-date" format. 1093 Values in the 'Subtag' field MUST be lowercase except as provided for 1094 in Section 3.1. 1096 3.3 Stability of IANA Registry Entries 1098 The stability of entries and their meaning in the registry is 1099 critical to the long term stability of language tags. The rules in 1100 this section guarantee that a specific language tag's meaning is 1101 stable over time and will not change. 1103 These rules specifically deal with how changes to codes (including 1104 withdrawal and deprecation of codes) maintained by ISO 639, ISO 1105 15924, ISO 3166, and UN M.49 are reflected in the IANA Language 1106 Subtag Registry. Assignments to the IANA Language Subtag Registry 1107 MUST follow the following stability rules: 1109 1. Values in the fields 'Type', 'Subtag', 'Tag', 'Added', 1110 'Deprecated' and 'Preferred-Value' MUST NOT be changed and are 1111 guaranteed to be stable over time. 1113 2. Values in the 'Description' field MUST NOT be changed in a way 1114 that would invalidate previously-existing tags. They MAY be 1115 broadened somewhat in scope, changed to add information, or 1116 adapted to the most common modern usage. For example, countries 1117 occasionally change their official names: an historical example 1118 of this would be "Upper Volta" changing to "Burkina Faso". 1120 3. Values in the field 'Prefix' MAY be added to records of type 1121 'variant' via the registration process. 1123 4. Values in the field 'Prefix' MAY be modified, so long as the 1124 modifications broaden the set of prefixes. That is, a prefix 1125 MAY be replaced by one of its own prefixes. For example, the 1126 prefix "en-US" could be replaced by "en", but not by the 1127 prefixes "en-Latn", "fr", or "en-US-boont". If one of those 1128 prefixes were needed, a new Prefix SHOULD be registered. 1130 5. Values in the field 'Prefix' MUST NOT be removed. 1132 6. The field 'Comments' MAY be added, changed, modified, or removed 1133 via the registration process or any of the processes or 1134 considerations described in this section. 1136 7. The field 'Suppress-Script' MAY be added or removed via the 1137 registration process. 1139 8. Codes assigned by ISO 639, ISO 15924, and ISO 3166 that do not 1140 conflict with existing subtags of the associated type and whose 1141 meaning is not the same as an existing subtag of the same type 1142 are entered into the IANA registry as new records. 1144 9. Codes assigned by ISO 639, ISO 15924, or ISO 3166 that are 1145 withdrawn by their respective maintenance or registration 1146 authority remain valid in language tags. A 'Deprecated' field 1147 containing the date of withdrawal is added to the record. If a 1148 new record of the same type is added that represents a 1149 replacement value, then a 'Preferred-Value' field MAY also be 1150 added. The registration process MAY be used to add comments 1151 about the withdrawal of the code by the respective standard. 1153 Example The region code 'TL' was assigned to the country 'Timor- 1154 Leste', replacing the code 'TP' (which was assigned to 'East 1155 Timor' when it was under administration by Portugal). The 1156 subtag 'TP' remains valid in language tags, but its record 1157 contains the a 'Preferred-Value' of 'TL' and its field 1158 'Deprecated' contains the date the new code was assigned 1159 ('2004-07-06'). 1161 10. Codes assigned by ISO 639, ISO 15924, or ISO 3166 that conflict 1162 with existing subtags of the associated type, including subtags 1163 that are deprecated, MUST NOT be entered into the registry. The 1164 following additional considerations apply to subtag values that 1165 are reassigned: 1167 A. For ISO 639 codes, if the newly assigned code's meaning is 1168 not represented by a subtag in the IANA registry, the 1169 Language Subtag Reviewer, as described in Section 3.4, SHALL 1170 prepare a proposal for entering in the IANA registry as soon 1171 as practical a registered language subtag as an alternate 1172 value for the new code. The form of the registered language 1173 subtag will be at the discretion of the Language Subtag 1174 Reviewer and MUST conform to other restrictions on language 1175 subtags in this document. 1177 B. For all subtags whose meaning is derived from an external 1178 standard (i.e. ISO 639, ISO 15924, ISO 3166, or UN M.49), 1179 if a new meaning is assigned to an existing code and the new 1180 meaning broadens the meaning of that code, then the meaning 1181 for the associated subtag MAY be changed to match. The 1182 meaning of a subtag MUST NOT be narrowed, however, as this 1183 can result in an unknown proportion of the existing uses of 1184 a subtag becoming invalid. Note: ISO 639 MA/RA has adopted 1185 a similar stability policy. 1187 C. For ISO 15924 codes, if the newly assigned code's meaning is 1188 not represented by a subtag in the IANA registry, the 1189 Language Subtag Reviewer, as described in Section 3.4, SHALL 1190 prepare a proposal for entering in the IANA registry as soon 1191 as practical a registered variant subtag as an alternate 1192 value for the new code. The form of the registered variant 1193 subtag will be at the discretion of the Language Subtag 1194 Reviewer and MUST conform to other restrictions on variant 1195 subtags in this document. 1197 D. For ISO 3166 codes, if the newly assigned code's meaning is 1198 associated with the same UN M.49 code as another 'region' 1199 subtag, then the existing region subtag remains as the 1200 preferred value for that region and no new entry is created. 1201 A comment MAY be added to the existing region subtag 1202 indicating the relationship to the new ISO 3166 code. 1204 E. For ISO 3166 codes, if the newly assigned code's meaning is 1205 associated with a UN M.49 code that is not represented by an 1206 existing region subtag, then the Language Subtag Reviewer, 1207 as described in Section 3.4, SHALL prepare a proposal for 1208 entering the appropriate UN M.49 country code as an entry in 1209 the IANA registry. 1211 F. For ISO 3166 codes, if there is no associated UN numeric 1212 code, then the Language Subtag Reviewer SHALL petition the 1213 UN to create one. If there is no response from the UN 1214 within ninety days of the request being sent, the Language 1215 Subtag Reviewer SHALL prepare a proposal for entering in the 1216 IANA registry as soon as practical a registered variant 1217 subtag as an alternate value for the new code. The form of 1218 the registered variant subtag will be at the discretion of 1219 the Language Subtag Reviewer and MUST conform to other 1220 restrictions on variant subtags in this document. This 1221 situation is very unlikely to ever occur. 1223 11. UN M.49 has codes for both countries and areas (such as '276' 1224 for Germany) and geographical regions and sub-regions (such as 1225 '150' for Europe). UN M.49 country or area codes for which 1226 there is no corresponding ISO 3166 code SHOULD NOT be 1227 registered, except as a surrogate for an ISO 3166 code that is 1228 blocked from registration by an existing subtag. If such a code 1229 becomes necessary, then the registration authority for ISO 3166 1230 SHOULD first be petitioned to assign a code to the region. If 1231 the petition for a code assignment by ISO 3166 is refused or not 1232 acted on in a timely manner, the registration process described 1233 in Section 3.4 MAY then be used to register the corresponding UN 1234 M.49 code. At the time this document was written, there were 1235 only four such codes: 830 (Channel Islands), 831 (Guernsey), 832 1236 (Jersey), and 833 (Isle of Man). This way UN M.49 codes remain 1237 available as the value of last resort in cases where ISO 3166 1238 reassigns a deprecated value in the registry. 1240 12. Stability provisions apply to grandfathered tags with this 1241 exception: should all of the subtags in a grandfathered tag 1242 become valid subtags in the IANA registry, then the field 'Type' 1243 in that record is changed from 'grandfathered' to 'redundant'. 1244 Note that this will not affect language tags that match the 1245 grandfathered tag, since these tags will now match valid 1246 generative subtag sequences. For example, if the subtag 'gan' 1247 in the language tag "zh-gan" were to be registered as an 1248 extended language subtag, then the grandfathered tag "zh-gan" 1249 would be deprecated (but existing content or implementations 1250 that use "zh-gan" would remain valid). 1252 3.4 Registration Procedure for Subtags 1254 The procedure given here MUST be used by anyone who wants to use a 1255 subtag not currently in the IANA Language Subtag Registry. 1257 Only subtags of type 'language' and 'variant' will be considered for 1258 independent registration of new subtags. Handling of subtags needed 1259 for stability and subtags necessary to keep the registry synchronized 1260 with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits 1261 defined by this document are described in Section 3.2. Stability 1262 provisions are described in Section 3.3. 1264 This procedure MAY also be used to register or alter the information 1265 for the "Description", "Comments", "Deprecated", or "Prefix" fields 1266 in a subtag's record as described in Section 3.3. Changes to all 1267 other fields in the IANA registry are NOT permitted. 1269 Registering a new subtag or requesting modifications to an existing 1270 tag or subtag starts with the requester filling out the registration 1271 form reproduced below. Note that each response is not limited in 1272 size so that the request can adequately describe the registration. 1273 The fields in the "Record Requested" section SHOULD follow the 1274 requirements in Section 3.1. 1276 LANGUAGE SUBTAG REGISTRATION FORM 1277 1. Name of requester: 1278 2. E-mail address of requester: 1279 3. Record Requested: 1281 Type: 1282 Subtag: 1283 Description: 1284 Prefix: 1285 Preferred-Value: 1286 Deprecated: 1287 Suppress-Script: 1288 Comments: 1290 4. Intended meaning of the subtag: 1291 5. Reference to published description 1292 of the language (book or article): 1293 6. Any other relevant information: 1295 Figure 5 1297 The subtag registration form MUST be sent to 1298 for a two week review period before it can 1299 be submitted to IANA. (This is an open list and can be joined by 1300 sending a request to .) 1302 Variant and extlang subtags are always registered for use with a 1303 particular range of language tags. For example, the subtag 'rozaj' 1304 is intended for use with language tags that start with the primary 1305 language subtag "sl", since Resian is a dialect of Slovenian. Thus 1306 the subtag 'rozaj' could be included in tags such as "sl-Latn-rozaj" 1307 or "sl-IT-rozaj". This information is stored in the "Prefix" field 1308 in the registry. Variant registration requests are REQUIRED to 1309 include at least one "Prefix" field in the registration form. 1311 The 'Prefix' field for a given registered subtag exists in the IANA 1312 registry as a guide to usage. Additional prefixes MAY be added by 1313 filing an additional registration form. In that form, the "Any other 1314 relevant information:" field MUST indicate that it is the addition of 1315 a prefix. 1317 Requests to add a prefix to a variant subtag that imply a different 1318 semantic meaning will probably be rejected. For example, a request 1319 to add the prefix "de" to the subtag 'nedis' so that the tag "de- 1320 nedis" represented some German dialect would be rejected. The 1321 'nedis' subtag represents a particular Slovenian dialect and the 1322 additional registration would change the semantic meaning assigned to 1323 the subtag. A separate subtag SHOULD be proposed instead. 1325 The 'Description' field MUST contain a description of the tag being 1326 registered written or transcribed into the Latin script; it MAY also 1327 include a description in a non-Latin script. Non-ASCII characters 1328 MUST be escaped using the syntax described in Section 3.1. The 1329 'Description' field is used for identification purposes and doesn't 1330 necessarily represent the actual native name of the language or 1331 variation or to be in any particular language. 1333 While the 'Description' field itself is not guaranteed to be stable 1334 and errata corrections MAY be undertaken from time to time, attempts 1335 to provide translations or transcriptions of entries in the registry 1336 itself will probably be frowned upon by the community or rejected 1337 outright, as changes of this nature have an impact on the provisions 1338 in Section 3.3. 1340 The Language Subtag Reviewer is responsible for responding to 1341 requests for the registration of subtags through the registration 1342 process and is appointed by the IESG. 1344 When the two week period has passed the Language Subtag Reviewer 1345 either forwards the record to be inserted or modified to 1346 iana@iana.org according to the procedure described in Section 3.2, or 1347 rejects the request because of significant objections raised on the 1348 list or due to problems with constraints in this document (which MUST 1349 be explicitly cited). The reviewer MAY also extend the review period 1350 in two week increments to permit further discussion. The reviewer 1351 MUST indicate on the list whether the registration has been accepted, 1352 rejected, or extended following each two week period. 1354 Note that the reviewer MAY raise objections on the list if he or she 1355 so desires. The important thing is that the objection MUST be made 1356 publicly. 1358 The applicant is free to modify a rejected application with 1359 additional information and submit it again; this restarts the two 1360 week comment period. 1362 Decisions made by the reviewer MAY be appealed to the IESG [RFC2028] 1363 under the same rules as other IETF decisions [RFC2026]. 1365 All approved registration forms are available online in the directory 1366 http://www.iana.org/numbers.html under "languages". 1368 Updates or changes to existing records follow the same procedure as 1369 new registrations. The Language Subtag Reviewer decides whether 1370 there is consensus to update the registration following the two week 1371 review period; normally objections by the original registrant will 1372 carry extra weight in forming such a consensus. 1374 Registrations are permanent and stable. Once registered, subtags 1375 will not be removed from the registry and will remain a valid way in 1376 which to specify a specific language or variant. 1378 Note: The purpose of the "Description" in the registration form is 1379 intended as an aid to people trying to verify whether a language is 1380 registered or what language or language variation a particular subtag 1381 refers to. In most cases, reference to an authoritative grammar or 1382 dictionary of that language will be useful; in cases where no such 1383 work exists, other well known works describing that language or in 1384 that language MAY be appropriate. The subtag reviewer decides what 1385 constitutes "good enough" reference material. This requirement is 1386 not intended to exclude particular languages or dialects due to the 1387 size of the speaker population or lack of a standardized orthography. 1388 Minority languages will be considered equally on their own merits. 1390 3.5 Possibilities for Registration 1392 Possibilities for registration of subtags or information about 1393 subtags include: 1395 o Primary language subtags for languages not listed in ISO 639 that 1396 are not variants of any listed or registered language MAY be 1397 registered. At the time this document was created there were no 1398 examples of this form of subtag. Before attempting to register a 1399 language subtag, there MUST be an attempt to register the language 1400 with ISO 639. Subtags MUST NOT be registered for codes that exist 1401 in ISO 639-1 or ISO 639-2, which are under consideration by the 1402 ISO 639 maintenance or registration authorities, or which have 1403 never been attempted for registration with those authorities. If 1404 ISO 639 has previously rejected a language for registration, it is 1405 reasonable to assume that there must be additional very compelling 1406 evidence of need before it will be registered in the IANA registry 1407 (to the extent that it is very unlikely that any subtags will be 1408 registered of this type). 1410 o Dialect or other divisions or variations within a language, its 1411 orthography, writing system, regional or historical usage, 1412 transliteration or other transformation, or distinguishing 1413 variation MAY be registered as variant subtags. An example is the 1414 'rozaj' subtag (the Resian dialect of Slovenian). 1416 o The addition or maintenance of fields (generally of an 1417 informational nature) in Tag or Subtag records as described in 1418 Section 3.1 and subject to the stability provisions in 1419 Section 3.3. This includes descriptions; comments; deprecation 1420 and preferred values for obsolete or withdrawn codes; or the 1421 addition of script or extlang information to primary language 1422 subtags. 1424 o The addition of records and related field value changes necessary 1425 to reflect assignments made by ISO 639, ISO 15924, ISO 3166, and 1426 UN M.49 as described in Section 3.3. 1428 This document leaves the decision on what subtags or changes to 1429 subtags are appropriate (or not) to the registration process 1430 described in Section 3.4. 1432 Note: four character primary language subtags are reserved to allow 1433 for the possibility of alpha4 codes in some future addition to the 1434 ISO 639 family of standards. 1436 ISO 639 defines a maintenance agency for additions to and changes in 1437 the list of languages in ISO 639. This agency is: 1439 International Information Centre for Terminology (Infoterm) 1440 Aichholzgasse 6/12, AT-1120 1441 Wien, Austria 1442 Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72 1444 ISO 639-2 defines a maintenance agency for additions to and changes 1445 in the list of languages in ISO 639-2. This agency is: 1447 Library of Congress 1448 Network Development and MARC Standards Office 1449 Washington, D.C. 20540 USA 1450 Phone: +1 202 707 6237 Fax: +1 202 707 0115 1451 URL: http://www.loc.gov/standards/iso639 1453 The maintenance agency for ISO 3166 (country codes) is: 1455 ISO 3166 Maintenance Agency 1456 c/o International Organization for Standardization 1457 Case postale 56 1458 CH-1211 Geneva 20 Switzerland 1459 Phone: +41 22 749 72 33 Fax: +41 22 749 73 49 1460 URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html 1462 The registration authority for ISO 15924 (script codes) is: 1464 Unicode Consortium Box 391476 1465 Mountain View, CA 94039-1476, USA 1466 URL: http://www.unicode.org/iso15924 1468 The Statistics Division of the United Nations Secretariat maintains 1469 the Standard Country or Area Codes for Statistical Use and can be 1470 reached at: 1472 Statistical Services Branch 1473 Statistics Division 1474 United Nations, Room DC2-1620 1475 New York, NY 10017, USA 1477 Fax: +1-212-963-0623 1478 E-mail: statistics@un.org 1479 URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm 1481 3.6 Extensions and Extensions Registry 1483 Extension subtags are those introduced by single character subtags 1484 ("singletons") other than 'x'. They are reserved for the generation 1485 of identifiers which contain a language component, and are compatible 1486 with applications that understand language tags. 1488 The structure and form of extensions are defined by this document so 1489 that implementations can be created that are forward compatible with 1490 applications that might be created using singletons in the future. 1491 In addition, defining a mechanism for maintaining singletons will 1492 lend stability to this document by reducing the likely need for 1493 future revisions or updates. 1495 Single character subtags are assigned by IANA using the "IETF 1496 Consensus" policy defined by [RFC2434]. This policy requires the 1497 development of an RFC, which SHALL define the name, purpose, 1498 processes, and procedures for maintaining the subtags. The 1499 maintaining or registering authority, including name, contact email, 1500 discussion list email, and URL location of the registry MUST be 1501 indicated clearly in the RFC. The RFC MUST specify or include each 1502 of the following: 1504 o The specification MUST reference the specific version or revision 1505 of this document that governs its creation and MUST reference this 1506 section of this document. 1508 o The specification and all subtags defined by the specification 1509 MUST follow the ABNF and other rules for the formation of tags and 1510 subtags as defined in this document. In particular it MUST 1511 specify that case is not significant and that subtags MUST NOT 1512 exceed eight characters in length. 1514 o The specification MUST specify a canonical representation. 1516 o The specification of valid subtags MUST be available over the 1517 Internet and at no cost. 1519 o The specification MUST be in the public domain or available via a 1520 royalty-free license acceptable to the IETF and specified in the 1521 RFC. 1523 o The specification MUST be versioned and each version of the 1524 specification MUST be numbered, dated, and stable. 1526 o The specification MUST be stable. That is, extension subtags, 1527 once defined by a specification, MUST NOT be retracted or change 1528 in meaning in any substantial way. 1530 o The specification MUST include in a separate section the 1531 registration form reproduced in this section (below) to be used in 1532 registering the extension upon publication as an RFC. 1534 o IANA MUST be informed of changes to the contact information and 1535 URL for the specification. 1537 IANA will maintain a registry of allocated single character 1538 (singleton) subtags. This registry MUST use the record-jar format 1539 described by the ABNF in Section 3.1. Upon publication of an 1540 extension as an RFC, the maintaining authority defined in the RFC 1541 MUST forward this registration form to iesg@ietf.org, who MUST 1542 forward the request to iana@iana.org. The maintaining authority of 1543 the extension MUST maintain the accuracy of the record by sending an 1544 updated full copy of the record to iana@iana.org with the subject 1545 line "LANGUAGE TAG EXTENSION UPDATE" whenever content changes. Only 1546 the 'Comments', 'Contact_Email', 'Mailing_List', and 'URL' fields MAY 1547 be modified in these updates. 1549 Failure to maintain this record, the corresponding registry, or meet 1550 other conditions imposed by this section of this document MAY be 1551 appealed to the IESG [RFC2028] under the same rules as other IETF 1552 decisions (see [RFC2026]) and MAY result in the authority to maintain 1553 the extension being withdrawn or reassigned by the IESG. 1555 %% 1556 Identifier: 1557 Description: 1558 Comments: 1559 Added: 1560 RFC: 1561 Authority: 1562 Contact_Email: 1563 Mailing_List: 1564 URL: 1565 %% 1567 Figure 6: Format of Records in the Language Tag Extensions Registry 1569 'Identifier' contains the single character subtag (singleton) 1570 assigned to the extension. The Internet-Draft submitted to define 1571 the extension SHOULD specify which letter or digit to use, although 1572 the IESG MAY change the assignment when approving the RFC. 1574 'Description' contains the name and description of the extension. 1576 'Comments' is an OPTIONAL field and MAY contain a broader description 1577 of the extension. 1579 'Added' contains the date the RFC was published in the "full-date" 1580 format specified in [RFC3339]. For example: 2004-06-28 represents 1581 June 28, 2004, in the Gregorian calendar. 1583 'RFC' contains the RFC number assigned to the extension. 1585 'Authority' contains the name of the maintaining authority for the 1586 extension. 1588 'Contact_Email' contains the email address used to contact the 1589 maintaining authority. 1591 'Mailing_List' contains the URL or subscription email address of the 1592 mailing list used by the maintaining authority. 1594 'URL' contains the URL of the registry for this extension. 1596 The determination of whether an Internet-Draft meets the above 1597 conditions and the decision to grant or withhold such authority rests 1598 solely with the IESG, and is subject to the normal review and appeals 1599 process associated with the RFC process. 1601 Extension authors are strongly cautioned that many (including most 1602 well-formed) processors will be unaware of any special relationships 1603 or meaning inherent in the order of extension subtags. Extension 1604 authors SHOULD avoid subtag relationships or canonicalization 1605 mechanisms that interfere with matching or with length restrictions 1606 that sometimes exist in common protocols where the extension is used. 1607 In particular, applications MAY truncate the subtags in doing 1608 matching or in fitting into limited lengths, so it is RECOMMENDED 1609 that the most significant information be in the most significant 1610 (left-most) subtags, and that the specification gracefully handle 1611 truncated subtags. 1613 When a language tag is to be used in a specific, known, protocol, it 1614 is RECOMMENDED that that the language tag not contain extensions not 1615 supported by that protocol. In addition, note that some protocols 1616 MAY impose upper limits on the length of the strings used to store or 1617 transport the language tag. 1619 3.7 Initialization of the Registries 1621 Upon adoption of this document an initial version of the Language 1622 Subtag Registry containing the various subtags initially valid in a 1623 language tag is necessary. This collection of subtags, along with a 1624 description of the process used to create it, is described by 1625 [initial-registry]. 1627 Registrations that are in process under the rules defined in 1628 [RFC3066] when this document is adopted MAY be completed under the 1629 former rules, at the discretion of the language tag reviewer. Any 1630 new registrations submitted after the adoption of this document MUST 1631 be rejected. 1633 An initial version of the Language Extension Registry described in 1634 Section 3.6 is also needed. The Language Extension Registry SHALL be 1635 initialized with a single record containing a single field of type 1636 "File-Date" as a placeholder for future assignments. 1638 4. Formation and Processing of Language Tags 1640 This section addresses how to use the information in the registry 1641 with the tag syntax to choose, form and process language tags. 1643 4.1 Choice of Language Tag 1645 One is sometimes faced with the choice between several possible tags 1646 for the same body of text. 1648 Interoperability is best served when all users use the same language 1649 tag in order to represent the same language. If an application has 1650 requirements that make the rules here inapplicable, then that 1651 application risks damaging interoperability. It is strongly 1652 RECOMMENDED that users not define their own rules for language tag 1653 choice. 1655 Subtags SHOULD only be used where they add useful distinguishing 1656 information; extraneous subtags interfere with the meaning, 1657 understanding, and processing of language tags. In particular, users 1658 and implementations SHOULD follow the 'Prefix' and 'Suppress-Script' 1659 fields in the registry (defined in Section 3.1): these fields provide 1660 guidance on when specific additional subtags SHOULD (and SHOULD NOT) 1661 be used in a language tag. 1663 Of particular note, many applications can benefit from the use of 1664 script subtags in language tags, as long as the use is consistent for 1665 a given context. Script subtags were not formally defined in RFC 1666 3066 and their use can affect matching and subtag identification by 1667 implementations of RFC 3066, as these subtags appear between the 1668 primary language and region subtags. For example, if a user requests 1669 content in an implementation of Section 2.5 of [RFC3066] using the 1670 language range "en-US", content labeled "en-Latn-US" will not match 1671 the request. Therefore it is important to know when script subtags 1672 will customarily be used and when they ought not be used. In the 1673 registry, the Suppress-Script field helps ensure greater 1674 compatibility between the language tags generated according to the 1675 rules in this document and language tags and tag processors or 1676 consumers based on RFC 3066 by defining when users SHOULD NOT include 1677 a script subtag with a particular primary language subtag. 1679 Extended language subtags (type 'extlang' in the registry, see 1680 Section 3.1) also appear between the primary language and region 1681 subtags and are reserved for future standardization. Applications 1682 might benefit from their judicious use in forming language tags in 1683 the future. Similar recommendations are expected to apply to their 1684 use as apply to script subtags. 1686 Standards, protocols and applications that reference this document 1687 normatively but apply different rules to the ones given in this 1688 section MUST specify how the procedure varies from the one given 1689 here. 1691 The choice of subtags used to form a language tag SHOULD be guided by 1692 the following rules: 1694 1. Use as precise a tag as possible, but no more specific than is 1695 justified. Avoid using subtags that are not important for 1696 distinguishing content in an application. 1698 * For example, 'de' might suffice for tagging an email written 1699 in German, while "de-CH-1996" is probably unnecessarily 1700 precise for such a task. 1702 2. The script subtag SHOULD NOT be used to form language tags unless 1703 the script adds some distinguishing information to the tag. The 1704 field 'Suppress-Script' in the primary language record in the 1705 registry indicates which script subtags do not add distinguishing 1706 information for most applications. 1708 * For example, the subtag 'Latn' should not be used with the 1709 primary language 'en' because nearly all English documents are 1710 written in the Latin script and it adds no distinguishing 1711 information. However, if a document were written in English 1712 mixing Latin script with another script such as Braille 1713 ('Brai'), then it might be appropriate to choose to indicate 1714 both scripts to aid in content selection, such as the 1715 application of a style sheet. 1717 3. If a tag or subtag has a 'Preferred-Value' field in its registry 1718 entry, then the value of that field SHOULD be used to form the 1719 language tag in preference to the tag or subtag in which the 1720 preferred value appears. 1722 * For example, use 'he' for Hebrew in preference to 'iw'. 1724 4. The 'und' (Undetermined) primary language subtag SHOULD NOT be 1725 used to label content, even if the language is unknown. Omitting 1726 the language tag altogether is preferred to using a tag with a 1727 primary language subtag of 'und'. The 'und' subtag MAY be useful 1728 for protocols that require a language tag to be provided. The 1729 'und' subtag MAY also be useful when matching language tags in 1730 certain situations. 1732 5. The 'mul' (Multiple) primary language subtag SHOULD NOT be used 1733 whenever the protocol allows the separate tags for multiple 1734 languages, as is the case for the Content-Language header in 1735 HTTP. The 'mul' subtag conveys little useful information: 1736 content in multiple languages SHOULD individually tag the 1737 languages where they appear or otherwise indicate the actual 1738 language in preference to the 'mul' subtag. 1740 6. The same variant subtag SHOULD NOT be used more than once within 1741 a language tag. 1743 * For example, do not use "de-DE-1901-1901". 1745 To ensure consistent backward compatibility, this document contains 1746 several provisions to account for potential instability in the 1747 standards used to define the subtags that make up language tags. 1748 These provisions mean that no language tag created under the rules in 1749 this document will become obsolete. 1751 4.2 Meaning of the Language Tag 1753 The relationship between the tag and the information it relates to is 1754 defined by the context in which the tag appears. Accordingly, this 1755 section gives only possible examples of its usage. 1757 o For a single information object, the associated language tags 1758 might be interpreted as the set of languages that is necessary for 1759 a complete comprehension of the complete object. Example: Plain 1760 text documents. 1762 o For an aggregation of information objects, the associated language 1763 tags could be taken as the set of languages used inside components 1764 of that aggregation. Examples: Document stores and libraries. 1766 o For information objects whose purpose is to provide alternatives, 1767 the associated language tags could be regarded as a hint that the 1768 content is provided in several languages, and that one has to 1769 inspect each of the alternatives in order to find its language or 1770 languages. In this case, the presence of multiple tags might not 1771 mean that one needs to be multi-lingual to get complete 1772 understanding of the document. Example: MIME multipart/ 1773 alternative. 1775 o In markup languages, such as HTML and XML, language information 1776 can be added to each part of the document identified by the markup 1777 structure (including the whole document itself). For example, one 1778 could write C'est la vie. inside a 1779 Norwegian document; the Norwegian-speaking user could then access 1780 a French-Norwegian dictionary to find out what the marked section 1781 meant. If the user were listening to that document through a 1782 speech synthesis interface, this formation could be used to signal 1783 the synthesizer to appropriately apply French text-to-speech 1784 pronunciation rules to that span of text, instead of applying the 1785 inappropriate Norwegian rules. 1787 Language tags are related when they contain a similar sequence of 1788 subtags. For example, if a language tag B contains language tag A as 1789 a prefix, then B is typically "narrower" or "more specific" than A. 1790 Thus "zh-Hant-TW" is more specific than "zh-Hant". 1792 This relationship is not guaranteed in all cases: specifically, 1793 languages that begin with the same sequence of subtags are NOT 1794 guaranteed to be mutually intelligible, although they might be. For 1795 example, the tag "az" shares a prefix with both "az-Latn" 1796 (Azerbaijani written using the Latin script) and "az-Cyrl" 1797 (Azerbaijani written using the Cyrillic script). A person fluent in 1798 one script might not be able to read the other, even though the text 1799 might be identical. Content tagged as "az" most probably is written 1800 in just one script and thus might not be intelligible to a reader 1801 familiar with the other script. 1803 4.3 Length Considerations 1805 [RFC3066] did not provide an upper limit on the size of language 1806 tags. While RFC 3066 did define the semantics of particular subtags 1807 in such a way that most language tags consisted of language and 1808 region subtags with a combined total length of up to six characters, 1809 larger registered tags were not only possible but were actually 1810 registered. 1812 Neither the language tag syntax nor other requirements in this 1813 document impose a fixed upper limit on the number of subtags in a 1814 language tag (and thus an upper bound on the size of a tag). The 1815 language tag syntax suggests that, depending on the specific 1816 language, more subtags (and thus a longer tag) are sometimes 1817 necessary to completely identify the language for certain 1818 applications; thus it is possible to envision long or complex subtag 1819 sequences. 1821 4.3.1 Working with Limited Buffer Sizes 1823 Some applications and protocols are forced to allocate fixed buffer 1824 sizes or otherwise limit the length of a language tag. A conformant 1825 implementation or specification MAY refuse to support the storage of 1826 language tags which exceed a specified length. Any such limitation 1827 SHOULD be clearly documented, and such documentation SHOULD include 1828 what happens to longer tags (for example, whether an error value is 1829 generated or the language tag is truncated). A protocol that allows 1830 tags to be truncated at an arbitrary limit, without giving any 1831 indication of what that limit is, has the potential for causing harm 1832 by changing the meaning of tags in substantial ways. 1834 In practice, most language tags do not require more than a few 1835 subtags and will not approach reasonably sized buffer limitations: 1836 see Section 4.1. 1838 Some specifications or protocols have limits on tag length but do not 1839 have a fixed length limitation. For example, [RFC2231] has no 1840 explicit length limitation: the length available for the language tag 1841 is constrained by the length of other header components (such as the 1842 charset's name) coupled with the 76 character limit in [RFC2047]. 1843 Thus the "limit" might be 50 or more characters, but it could 1844 potentially be quite small. 1846 The considerations for assigning a buffer limit are: 1848 Implementations SHOULD NOT truncate language tags unless the 1849 meaning of the tag is purposefully being changed, or unless the 1850 tag does not fit into a limited buffer size specified by a 1851 protocol for storage or transmission. 1853 Implementations SHOULD warn the user when a tag is truncated since 1854 truncation changes the semantic meaning of the tag. 1856 Implementations of protocols or specifications that are space 1857 constrained but do not have a fixed limit SHOULD use the longest 1858 possible tag in preference to truncation. 1860 Protocols or specifications that specify limited buffer sizes for 1861 language tags MUST allow for language tags of up to 33 characters. 1863 Protocols or specifications that specify limited buffer sizes for 1864 language tags SHOULD allow for language tags of at least 42 1865 characters. 1867 The following illustration shows how the 42-character recommendation 1868 was derived. The combination of language and extended language 1869 subtags was chosen for future compatibility. At up to 15 characters, 1870 this combination is longer than the longest possible primary language 1871 subtag (8 characters): 1873 language = 3 (ISO 639-2; ISO 639-1 requires 2) 1874 extlang1 = 4 (each subsequent subtag includes '-') 1875 extlang2 = 4 (unlikely: needs prefix="language-extlang1") 1876 extlang3 = 4 (extremely unlikely) 1877 script = 5 (if not suppressed: see Section 4.1) 1878 region = 4 (UN M.49; ISO 3166 requires 3) 1879 variant1 = 9 (MUST have language as a prefix) 1880 variant2 = 9 (MUST have language-variant1 as a prefix) 1882 total = 42 characters 1884 Figure 7: Derivation of the Limit on Tag Length 1886 4.3.2 Truncation of Language Tags 1888 Truncation of a language tag alters the meaning of the tag, and thus 1889 SHOULD be avoided. However, truncation of language tags is sometimes 1890 necessary due to limited buffer sizes. Such truncation MUST NOT 1891 permit a subtag to be chopped off in the middle or the formation of 1892 invalid tags (for example, one ending with the "-" character). 1894 This means that applications or protocols which truncate tags MUST do 1895 so by progressively removing subtags along with their preceding "-" 1896 from the right side of the language tag until the tag is short enough 1897 for the given buffer. If the resulting tag ends with a single- 1898 character subtag, that subtag and its preceding "-" MUST also be 1899 removed. For example: 1901 Tag to truncate: zh-Hant-CN-variant1-a-extend1-x-wadegile-private1 1902 1. zh-Latn-CN-variant1-a-extend1-x-wadegile 1903 2. zh-Latn-CN-variant1-a-extend1 1904 3. zh-Latn-CN-variant1 1905 4. zh-Latn-CN 1906 5. zh-Latn 1907 6. zh 1909 Figure 8: Example of Tag Truncation 1911 4.4 Canonicalization of Language Tags 1913 Since a particular language tag is sometimes used by many processes, 1914 language tags SHOULD always be created or generated in a canonical 1915 form. 1917 A language tag is in canonical form when: 1919 1. The tag is well-formed according the rules in Section 2.1 and 1920 Section 2.2. 1922 2. Subtags of type 'Region' that have a Preferred-Value mapping in 1923 the IANA registry (see Section 3.1) SHOULD be replaced with their 1924 mapped value. Note: In rare cases the mapped value will also 1925 have a Preferred-Value. 1927 3. Redundant or grandfathered tags that have a Preferred-Value 1928 mapping in the IANA registry (see Section 3.1) MUST be replaced 1929 with their mapped value. These items are either deprecated 1930 mappings created before the adoption of this document (such as 1931 the mapping of "no-nyn" to "nn" or "i-klingon" to "tlh") or are 1932 the result of later registrations or additions to this document 1933 (for example, "zh-guoyu" might be mapped to a language-extlang 1934 combination such as "zh-cmn" by some future update of this 1935 document). 1937 4. Other subtags that have a Preferred-Value mapping in the IANA 1938 registry (see Section 3.1) MUST be replaced with their mapped 1939 value. These items consist entirely of clerical corrections to 1940 ISO 639-1 in which the deprecated subtags have been maintained 1941 for compatibility purposes. 1943 5. If more than one extension subtag sequence exists, the extension 1944 sequences are ordered into case-insensitive ASCII order by 1945 singleton subtag. 1947 Example: The language tag "en-A-aaa-B-ccc-bbb-x-xyz" is in canonical 1948 form, while "en-B-ccc-bbb-A-aaa-X-xyz" is well-formed but not in 1949 canonical form. 1951 Example: The language tag "en-BU" (English as used in Burma) is not 1952 canonical because the 'BU' subtag has a canonical mapping to 'MM' 1953 (Myanmar), although the tag "en-BU" maintains its validity. 1955 Canonicalization of language tags does not imply anything about the 1956 use of upper or lowercase letters when processing or comparing 1957 subtags (and as described in Section 2.1). All comparisons MUST be 1958 performed in a case-insensitive manner. 1960 When performing canonicalization of language tags, processors MAY 1961 regularize the case of the subtags (that is, this process is 1962 OPTIONAL), following the case used in the registry. Note that this 1963 corresponds to the following casing rules: uppercase all non-initial 1964 two-letter subtags; titlecase all non-initial four-letter subtags; 1965 lowercase everything else. 1967 Note: Case folding of ASCII letters in certain locales, unless 1968 carefully handled, sometimes produces non-ASCII character values. 1969 The Unicode Character Database file "SpecialCasing.txt" defines the 1970 specific cases that are known to cause problems with this. In 1971 particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is 1972 uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE). 1973 Implementers SHOULD specify a locale-neutral casing operation to 1974 ensure that case folding of subtags does not produce this value, 1975 which is illegal in language tags. For example, if one were to 1976 uppercase the region subtag 'in' using Turkish locale rules, the 1977 sequence U+0130 U+004E would result instead of the expected 'IN'. 1979 Note: if the field 'Deprecated' appears in a registry record without 1980 an accompanying 'Preferred-Value' field, then that tag or subtag is 1981 deprecated without a replacement. Validating processors SHOULD NOT 1982 generate tags that include these values, although the values are 1983 canonical when they appear in a language tag. 1985 An extension MUST define any relationships that exist between the 1986 various subtags in the extension and thus MAY define an alternate 1987 canonicalization scheme for the extension's subtags. Extensions MAY 1988 define how the order of the extension's subtags are interpreted. For 1989 example, an extension could define that its subtags are in canonical 1990 order when the subtags are placed into ASCII order: that is, "en-a- 1991 aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension might 1992 define that the order of the subtags influences their semantic 1993 meaning (so that "en-b-ccc-bbb-aaa" has a different value from "en-b- 1994 aaa-bbb-ccc"). However, extension specifications SHOULD be designed 1995 so that they are tolerant of the typical processes described in 1996 Section 3.6. 1998 4.5 Considerations for Private Use Subtags 2000 Private use subtags, like all other subtags, MUST conform to the 2001 format and content constraints in the ABNF. Private use subtags have 2002 no meaning outside the private agreement between the parties that 2003 intend to use or exchange language tags that employ them. The same 2004 subtags MAY be used with a different meaning under a separate private 2005 agreement. They SHOULD NOT be used where alternatives exist and 2006 SHOULD NOT be used in content or protocols intended for general use. 2008 Private use subtags are simply useless for information exchange 2009 without prior arrangement. The value and semantic meaning of private 2010 use tags and of the subtags used within such a language tag are not 2011 defined by this document. 2013 Subtags defined in the IANA registry as having a specific private use 2014 meaning convey more information that a purely private use tag 2015 prefixed by the singleton subtag 'x'. For applications this 2016 additional information MAY be useful. 2018 For example, the region subtags 'AA', 'ZZ' and in the ranges 2019 'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166 private use codes) MAY 2020 be used to form a language tag. A tag such as "zh-Hans-XQ" conveys a 2021 great deal of public, interchangeable information about the language 2022 material (that it is Chinese in the simplified Chinese script and is 2023 suitable for some geographic region 'XQ'). While the precise 2024 geographic region is not known outside of private agreement, the tag 2025 conveys far more information than an opaque tag such as "x-someLang", 2026 which contains no information about the language subtag or script 2027 subtag outside of the private agreement. 2029 However, in some cases content tagged with private use subtags MAY 2030 interact with other systems in a different and possibly unsuitable 2031 manner compared to tags that use opaque, privately defined subtags, 2032 so the choice of the best approach sometimes depends on the 2033 particular domain in question. 2035 5. IANA Considerations 2037 This section deals with the processes and requirements necessary for 2038 IANA to undertake to maintain the subtag and extension registries as 2039 defined by this document and in accordance with the requirements of 2040 [RFC2434]. 2042 The impact on the IANA maintainers of the two registries defined by 2043 this document will be a small increase in the frequency of new 2044 entries or updates. 2046 5.1 Language Subtag Registry 2048 Upon adoption of this document, the registry will be initialized by a 2049 companion document: [initial-registry]. The criteria and process for 2050 selecting the initial set of records is described in that document. 2051 The initial set of records represents no impact on IANA, since the 2052 work to create it will be performed externally. 2054 The new registry MUST be listed under "Language Tags" at 2055 , replacing the existing 2056 registrations defined by [RFC3066]. The existing set of registration 2057 forms and RFC 3066 registrations MUST be relabeled as "Language Tags 2058 (Obsolete)" and maintained (but not added to or modified). 2060 Future work on the Language Subtag Registry SHALL be limited to 2061 inserting or replacing whole records preformatted for IANA by the 2062 Language Subtag Reviewer as described in Section 3.2 of this 2063 document. This simplifies IANA's work by limiting it to placing the 2064 text in the appropriate location in the registry. 2066 Each record MUST be sent to iana@iana.org with a subject line 2067 indicating whether the enclosed record is an insertion of a new 2068 record (indicated by the word "INSERT" in the subject line) or a 2069 replacement of an existing record (indicated by the word "MODIFY" in 2070 the subject line). Records MUST NOT be deleted from the registry. 2071 IANA MUST place any inserted or modified records into the appropriate 2072 section of the language subtag registry, grouping the records by 2073 their 'Type' field. Inserted records MAY be placed anywhere in the 2074 appropriate section; there is no guarantee of the order of the 2075 records beyond grouping them together by 'Type'. Modified records 2076 MUST overwrite the record they replace. 2078 Included in any request to insert or modify records MUST be a new 2079 File-Date record. This record MUST be placed first in the registry. 2080 In the event that the File-Date record present in the registry has a 2081 later date then the record being inserted or modified, the existing 2082 record MUST be preserved. 2084 5.2 Extensions Registry 2086 The Language Tag Extensions registry will also be generated and sent 2087 to IANA as described in Section 3.6. This registry can contain at 2088 most 35 records and thus changes to this registry are expected to be 2089 very infrequent. 2091 Future work by IANA on the Language Tag Extensions Registry is 2092 limited to two cases. First, the IESG MAY request that new records 2093 be inserted into this registry from time to time. These requests 2094 MUST include the record to insert in the exact format described in 2095 Section 3.6. In addition, there MAY be occasional requests from the 2096 maintaining authority for a specific extension to update the contact 2097 information or URLs in the record. These requests MUST include the 2098 complete, updated record. IANA is not responsible for validating the 2099 information provided, only that it is properly formatted. It should 2100 reasonably be seen to come from the maintaining authority named in 2101 the record present in the registry. 2103 6. Security Considerations 2105 Language tags used in content negotiation, like any other information 2106 exchanged on the Internet, might be a source of concern because they 2107 might be used to infer the nationality of the sender, and thus 2108 identify potential targets for surveillance. 2110 This is a special case of the general problem that anything sent is 2111 visible to the receiving party and possibly to third parties as well. 2112 It is useful to be aware that such concerns can exist in some cases. 2114 The evaluation of the exact magnitude of the threat, and any possible 2115 countermeasures, is left to each application protocol (see BCP 72 2116 [RFC3552] for best current practice guidance on security threats and 2117 defenses). 2119 The language tag associated with a particular information item is of 2120 no consequence whatsoever in determining whether that content might 2121 contain possible homographs. The fact that a text is tagged as being 2122 in one language or using a particular script subtag provides no 2123 assurance whatsoever that it does not contain characters from scripts 2124 other than the one(s) associated with or specified by that language 2125 tag. 2127 Since there is no limit to the number of variant, private use, and 2128 extension subtags, and consequently no limit on the possible length 2129 of a tag, implementations need to guard against buffer overflow 2130 attacks. See Section 4.3 for details on language tag truncation, 2131 which can occur as a consequence of defenses against buffer overflow. 2133 Although the specification of valid subtags for an extension (see: 2134 Section 3.6) MUST be available over the Internet, implementations 2135 SHOULD NOT mechanically depend on it being always accessible, to 2136 prevent denial-of-service attacks. 2138 7. Character Set Considerations 2140 The syntax in this document requires that language tags use only the 2141 characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most 2142 character sets, so the composition of language tags should not have 2143 any character set issues. 2145 Rendering of characters based on the content of a language tag is not 2146 addressed in this memo. Historically, some languages have relied on 2147 the use of specific character sets or other information in order to 2148 infer how a specific character should be rendered (notably this 2149 applies to language and culture specific variations of Han ideographs 2150 as used in Japanese, Chinese, and Korean). When language tags are 2151 applied to spans of text, rendering engines sometimes use that 2152 information in deciding which font to use in the absence of other 2153 information, particularly where languages with distinct writing 2154 traditions use the same characters. 2156 8. Changes from RFC 3066 2158 The main goals for this revision of language tags were the following: 2160 *Compatibility.* All RFC 3066 language tags (including those in the 2161 IANA registry) remain valid in this specification. The changes in 2162 this document represent additional constraints on language tags. 2163 That is, in no case is the syntax more permissive and processors 2164 based on the ABNF and other provisions of RFC 3066 (such as those 2165 described in [XMLSchema]) will be able to process the tags described 2166 by this document. In addition, this document defines language tags 2167 in such as way as to ensure future compatibility. 2169 *Stability.* Because of changes in the past in the underlying ISO 2170 standards, a valid RFC 3066 language tag could become invalid or have 2171 its meaning change. This has the potential of invalidating content 2172 that may have an extensive shelf-life. In this specification, once a 2173 language tag is valid, it remains valid forever. 2175 *Validity.* The structure of language tags defined by this document 2176 makes it possible to determine if a particular tag is well-formed 2177 without regard for the actual content or "meaning" of the tag as a 2178 whole. This is important because the registry grows and underlying 2179 standards change over time. In addition, it must be possible to 2180 determine if a tag is valid (or not) for a given point in time in 2181 order to provide reproducible, testable results. This process must 2182 not be error-prone; otherwise implementations might give different 2183 results. By having an authoritative registry with specific 2184 versioning information, the validity of language tags at any point in 2185 time can be precisely determined (instead of interpolating values 2186 from many separate sources). 2188 *Utility.* It is sometimes important to be able to differentiate 2189 between written forms of a language -- for many implementations this 2190 is more important than distinguishing between the spoken variants of 2191 a language. Languages are written in a wide variety of different 2192 scripts, so this document provides for the generative use of ISO 2193 15924 script codes. Like the generative use of ISO language and 2194 country codes in RFC 3066, this allows combinations to be produced 2195 without resorting to the registration process. The addition of UN 2196 M.49 codes provides for the generation of language tags with regional 2197 scope, which is also required by some applications. 2199 The recast of the registry from containing whole language tags to 2200 subtags is a key part of this. An important feature of RFC 3066 was 2201 that it allowed generative use of subtags. This allows people to 2202 meaningfully use generated tags, without the delays in registering 2203 whole tags or the need to register all of the combinations that might 2204 be useful. 2206 The choice of placing the extended language and script subtags 2207 between the primary language and region subtags was widely debated. 2208 This design was chosen because the prevalent matching and content 2209 negotiation schemes rely on the subtags being arranged in order of 2210 increasing specificity. That is, the subtags that mark a greater 2211 barrier to mutual intelligibility appear left-most in a tag. For 2212 example, when selecting content written in Azerbaijani, the script 2213 (Arabic, Cyrillic, or Latin) represents a greater barrier to 2214 understanding than any regional variations (those associated with 2215 Azerbaijan or Iran, for example). Individuals who prefer documents 2216 in a particular script, but can deal with the minor regional 2217 differences, can therefore select appropriate content. Applications 2218 that do not deal with written content will continue to omit these 2219 subtags. 2221 *Extensibility.* Because of the widespread use of language tags, it 2222 is disruptive to have periodic revisions of the core specification, 2223 even in the face of demonstrated need. The extension mechanism 2224 provides for a way for independent RFCs to define extensions to 2225 language tags. These extensions have a very constrained, well- 2226 defined structure that prevent extensions from interfering with 2227 implementations of language tags defined in this document. 2229 The document also anticipates features of ISO 639-3 with the addition 2230 of the extended language subtags, as well as the possibility of other 2231 ISO 639 parts becoming useful for the formation of language tags in 2232 the future. 2234 The use and definition of private use tags has also been modified, to 2235 allow people to use private use subtags to extend or modify defined 2236 tags and to move as much information as possible out of private use 2237 and into the regular structure. 2239 The goal for each of these modifications is to reduce or eliminate 2240 the need for future revisions of this document. 2242 The specific changes in this document to meet these goals are: 2244 o Defines the ABNF and rules for subtags so that the category of all 2245 subtags can be determined without reference to the registry. 2247 o Adds the concept of well-formed vs. validating processors, 2248 defining the rules by which an implementation can claim to be one 2249 or the other. 2251 o Replaces the IANA language tag registry with a language subtag 2252 registry that provides a complete list of valid subtags in the 2253 IANA registry. This allows for robust implementation and ease of 2254 maintenance. The language subtag registry becomes the canonical 2255 source for forming language tags. 2257 o Provides a process that guarantees stability of language tags, by 2258 handling reuse of values by ISO 639, ISO 15924, and ISO 3166 in 2259 the event that they register a previously used value for a new 2260 purpose. 2262 o Allows ISO 15924 script code subtags and allows them to be used 2263 generatively. Defines a method for indicating in the registry 2264 when script subtags are necessary for a given language tag. 2266 o Adds the concept of a variant subtag and allows variants to be 2267 used generatively. 2269 o Adds the ability to use a class of UN M.49 tags for supra- 2270 national regions and to resolve conflicts in the assignment of ISO 2271 3166 codes. 2273 o Defines the private use tags in ISO 639, ISO 15924, and ISO 3166 2274 as the mechanism for creating private use language, script, and 2275 region subtags respectively. 2277 o Adds a well-defined extension mechanism. 2279 o Defines an extended language subtag, possibly for use with certain 2280 anticipated features of ISO 639-3. 2282 Ed Note: The following items are provided for the convenience of 2283 reviewers and will be removed from the final document. 2285 Changes between draft-ietf-ltru-registry-10 and this version are: 2287 o Changed the text describing extensions from "single-letter" to 2288 "single character" or "singleton" to be consistent with the ABNF 2289 and the WG's intentions (D.Ewell) 2291 o Made RFC 2047, RFC 2781, and RFC 3552 into informative references 2292 (#1095)(K.Karlsson) 2294 o Made modifications to clarify the difference between the Language 2295 Subtag Registry and the Language Extensions Registry (K.Karlsson) 2297 o Inserted some text to ensure that the Language Extensions Registry 2298 is initialized properly (#1103) (K.Karlsson) 2300 9. References 2302 9.1 Normative References 2304 [ISO10646] 2305 International Organization for Standardization, "ISO/IEC 2306 10646:2003. Information technology -- Universal Multiple- 2307 Octet Coded Character Set (UCS)", 2003. 2309 [ISO15924] 2310 International Organization for Standardization, "ISO 2311 15924:2004. Information and documentation -- Codes for the 2312 representation of names of scripts", January 2004. 2314 [ISO3166-1] 2315 International Organization for Standardization, "ISO 3166- 2316 1:1997. Codes for the representation of names of 2317 countries and their subdivisions -- Part 1: Country 2318 codes", 1997. 2320 [ISO639-1] 2321 International Organization for Standardization, "ISO 639- 2322 1:2002. Codes for the representation of names of languages 2323 -- Part 1: Alpha-2 code", 2002. 2325 [ISO639-2] 2326 International Organization for Standardization, "ISO 639- 2327 2:1998. Codes for the representation of names of languages 2328 -- Part 2: Alpha-3 code, first edition", 1998. 2330 [ISO646] International Organization for Standardization, "ISO/IEC 2331 646:1991, Information technology -- ISO 7-bit coded 2332 character set for information interchange.", 1991. 2334 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 2335 3", BCP 9, RFC 2026, October 1996. 2337 [RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in 2338 the IETF Standards Process", BCP 11, RFC 2028, 2339 October 1996. 2341 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2342 Requirement Levels", BCP 14, RFC 2119, March 1997. 2344 [RFC2234bis] 2345 Crocker, D. and P. Overell, "Augmented BNF for Syntax 2346 Specifications: ABNF", draft-crocker-abnf-rfc2234bis-00 2347 (work in progress), March 2005. 2349 [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an 2350 IANA Considerations Section in RFCs", BCP 26, RFC 2434, 2351 October 1998. 2353 [RFC2860] Carpenter, B., Baker, F., and M. Roberts, "Memorandum of 2354 Understanding Concerning the Technical Work of the 2355 Internet Assigned Numbers Authority", RFC 2860, June 2000. 2357 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 2358 Timestamps", RFC 3339, July 2002. 2360 [UN_M.49] Statistics Division, United Nations, "Standard Country or 2361 Area Codes for Statistical Use", UN Standard Country or 2362 Area Codes for Statistical Use, Revision 4 (United Nations 2363 publication, Sales No. 98.XVII.9, June 1999. 2365 9.2 Informative References 2367 [RFC1766] Alvestrand, H., "Tags for the Identification of 2368 Languages", RFC 1766, March 1995. 2370 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) 2371 Part Three: Message Header Extensions for Non-ASCII Text", 2372 RFC 2047, November 1996. 2374 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded 2375 Word Extensions: Character Sets, Languages, and 2376 Continuations", RFC 2231, November 1997. 2378 [RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 2379 10646", RFC 2781, February 2000. 2381 [RFC3066] Alvestrand, H., "Tags for the Identification of 2382 Languages", BCP 47, RFC 3066, January 2001. 2384 [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC 2385 Text on Security Considerations", BCP 72, RFC 3552, 2386 July 2003. 2388 [Unicode] Unicode Consortium, "The Unicode Consortium. The Unicode 2389 Standard, Version 4.1.0, defined by: The Unicode Standard, 2390 Version 4.0 (Boston, MA, Addison-Wesley, 2003. ISBN 0-321- 2391 18578-1), as amended by Unicode 4.0.1 2392 (http://www.unicode.org/versions/Unicode4.0.1) and by 2393 Unicode 4.1.0 2394 (http://www.unicode.org/versions/Unicode4.1.0).", 2395 March 2005. 2397 [XML10] Bray (et al), T., "Extensible Markup Language (XML) 1.0", 2398 02 2004. 2400 [XMLSchema] 2401 Biron, P., Ed. and A. Malhotra, Ed., "XML Schema Part 2: 2402 Datatypes Second Edition", 10 2004, < 2403 http://www.w3.org/TR/xmlschema-2/>. 2405 [initial-registry] 2406 Ewell, D., Ed., "Initial Language Subtag Registry", 2407 June 2005, . 2410 [iso639.principles] 2411 ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory 2412 Committee: Working principles for ISO 639 maintenance", 2413 March 2000, 2414 . 2417 [record-jar] 2418 Raymond, E., "The Art of Unix Programming", 2003. 2420 Authors' Addresses 2422 Addison Phillips (editor) 2423 Quest Software 2425 Email: addison.phillips@quest.com 2426 URI: http://www.inter-locale.com 2428 Mark Davis (editor) 2429 IBM 2431 Email: mark.davis@us.ibm.com 2433 Appendix A. Acknowledgements 2435 Any list of contributors is bound to be incomplete; please regard the 2436 following as only a selection from the group of people who have 2437 contributed to make this document what it is today. 2439 The contributors to RFC 3066 and RFC 1766, the precursors of this 2440 document, made enormous contributions directly or indirectly to this 2441 document and are generally responsible for the success of language 2442 tags. 2444 The following people (in alphabetical order) contributed to this 2445 document or to RFCs 1766 and 3066: 2447 Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet, 2448 Nathaniel Borenstein, Karen Broome, Eric Brunner, Sean M. Burke, M.T. 2449 Carrasco Benitez, Jeremy Carroll, John Clews, Jim Conklin, Peter 2450 Constable, John Cowan, Mark Crispin, Dave Crocker, Martin Duerst, 2451 Frank Ellerman, Michael Everson, Doug Ewell, Ned Freed, Tim Goodwin, 2452 Dirk-Willem van Gulik, Marion Gunn, Joel Halpren, Elliotte Rusty 2453 Harold, Paul Hoffman, Scott Hollenbeck, Richard Ishida, Olle 2454 Jarnefors, Kent Karlsson, John Klensin, Erkki Kolehmainen, Alain 2455 LaBonte, Eric Mader, Ira McDonald, Keith Moore, Chris Newman, 2456 Masataka Ohta, Dylan Pierce, Randy Presuhn, George Rhoten, Felix 2457 Sasaki, Markus Scherer, Keld Jorn Simonsen, Thierry Sourbier, Otto 2458 Stolz, Tex Texin, Andrea Vine, Rhys Weatherley, Misha Wolf, Francois 2459 Yergeau and many, many others. 2461 Very special thanks must go to Harald Tveit Alvestrand, who 2462 originated RFCs 1766 and 3066, and without whom this document would 2463 not have been possible. Special thanks must go to Michael Everson, 2464 who has served as language tag reviewer for almost the complete 2465 period since the publication of RFC 1766. Special thanks to Doug 2466 Ewell, for his production of the first complete subtag registry, and 2467 his work in producing a test parser for verifying language tags. 2469 Appendix B. Examples of Language Tags (Informative) 2471 Simple language subtag: 2473 de (German) 2475 fr (French) 2477 ja (Japanese) 2479 i-enochian (example of a grandfathered tag) 2481 Language subtag plus Script subtag: 2483 zh-Hant (Chinese written using the Traditional Chinese script) 2485 zh-Hans (Chinese written using the Simplified Chinese script) 2487 sr-Cyrl (Serbian written using the Cyrillic script) 2489 sr-Latn (Serbian written using the Latin script) 2491 Language-Script-Region: 2493 zh-Hans-CN (Chinese written using the Simplified script as used in 2494 mainland China) 2496 sr-Latn-CS (Serbian written using the Latin script as used in 2497 Serbia and Montenegro) 2499 Language-Variant: 2501 sl-rozaj (Resian dialect of Slovenian 2503 sl-nedis (Nadiza dialect of Slovenian) 2505 Language-Region-Variant: 2507 de-CH-1901 (German as used in Switzerland using the 1901 variant 2508 [orthography]) 2510 sl-IT-nedis (Slovenian as used in Italy, Nadiza dialect) 2512 Language-Script-Region-Variant: 2514 sl-Latn-IT-nedis (Nadiza dialect of Slovenian written using the 2515 Latin script as used in Italy. Note that this tag is NOT 2516 RECOMMENDED because subtag 'sl' has a Suppress-Script value of 2517 'Latn') 2519 Language-Region: 2521 de-DE (German for Germany) 2523 en-US (English as used in the United States) 2525 es-419 (Spanish appropriate for the Latin America and Caribbean 2526 region using the UN region code) 2528 Private use subtags: 2530 de-CH-x-phonebk 2532 az-Arab-x-AZE-derbend 2534 Extended language subtags (examples ONLY: extended languages MUST be 2535 defined by revision or update to this document): 2537 zh-min 2539 zh-min-nan-Hant-CN 2541 Private use registry values: 2543 x-whatever (private use using the singleton 'x') 2545 qaa-Qaaa-QM-x-southern (all private tags) 2547 de-Qaaa (German, with a private script) 2549 sr-Latn-QM (Serbian, Latin-script, private region) 2551 sr-Qaaa-CS (Serbian, private script, for Serbia and Montenegro) 2553 Tags that use extensions (examples ONLY: extensions MUST be defined 2554 by revision or update to this document or by RFC): 2556 en-US-u-islamCal 2558 zh-CN-a-myExt-x-private 2559 en-a-myExt-b-another 2561 Some Invalid Tags: 2563 de-419-DE (two region tags) 2565 a-DE (use of a single character subtag in primary position; note 2566 that there are a few grandfathered tags that start with "i-" that 2567 are valid) 2569 ar-a-aaa-b-bbb-a-ccc (two extensions with same single letter 2570 prefix) 2572 Intellectual Property Statement 2574 The IETF takes no position regarding the validity or scope of any 2575 Intellectual Property Rights or other rights that might be claimed to 2576 pertain to the implementation or use of the technology described in 2577 this document or the extent to which any license under such rights 2578 might or might not be available; nor does it represent that it has 2579 made any independent effort to identify any such rights. Information 2580 on the procedures with respect to rights in RFC documents can be 2581 found in BCP 78 and BCP 79. 2583 Copies of IPR disclosures made to the IETF Secretariat and any 2584 assurances of licenses to be made available, or the result of an 2585 attempt made to obtain a general license or permission for the use of 2586 such proprietary rights by implementers or users of this 2587 specification can be obtained from the IETF on-line IPR repository at 2588 http://www.ietf.org/ipr. 2590 The IETF invites any interested party to bring to its attention any 2591 copyrights, patents or patent applications, or other proprietary 2592 rights that may cover technology that may be required to implement 2593 this standard. Please address the information to the IETF at 2594 ietf-ipr@ietf.org. 2596 Disclaimer of Validity 2598 This document and the information contained herein are provided on an 2599 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 2600 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 2601 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 2602 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 2603 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 2604 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 2606 Copyright Statement 2608 Copyright (C) The Internet Society (2005). This document is subject 2609 to the rights, licenses and restrictions contained in BCP 78, and 2610 except as set forth therein, the authors retain all their rights. 2612 Acknowledgment 2614 Funding for the RFC Editor function is currently provided by the 2615 Internet Society.