Internet Engineering Task Force M. Davis Internet-Draft Google Intended status: BCP A. Phillips Expires: July 17, 2010 Lab126 Y. Umaoka IBM January 13, 2010 BCP 47 Extension U draft-davis-u-langtag-ext-00 Abstract This document specifies an Extension to BCP 47 which provides subtags that specify language and/or locale-based behavior or refinements to language tags, according to work done by the Unicode Consortium. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 17, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Davis, et al. Expires July 17, 2010 [Page 1] Internet-Draft BCP 47 Unicode Locale Extension January 2010 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 2. BCP47 Required Information . . . . . . . . . . . . . . . . . . 3 2.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1. Canonicalization . . . . . . . . . . . . . . . . . . . 5 2.2. Registration Form . . . . . . . . . . . . . . . . . . . . . 5 3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Davis, et al. Expires July 17, 2010 [Page 2] Internet-Draft BCP 47 Unicode Locale Extension January 2010 1. Introduction [BCP47] permits the definition and registration of language tag extensions "that contain a language component and are compatible with applications that understand language tags". This document defines an extension for identifying Unicode locale-based variations using language tags. The "singleton" identifier for this extension is 'u'. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. 2. BCP47 Required Information Language tags, as defined by [BCP47], are useful for identifying the language of content. They are also used as locale identifiers (or can be mapped to locales) in many operating environments and APIs. However, most such locale identifiers also provide additional "tailorings" or options for specific values within a language, culture, region, or other variation. This extension provides a mechanism for using these additional tailorings within language tags for general interchange. The maintaining authority for this extension's registry is the Unicode Consortium. Unicode defines common locale data and identifiers for this data: +---------------+---------------------------------------------------+ | Item | Value | +---------------+---------------------------------------------------+ | Name | Unicode Consortium | | Contact Email | cldr@unicode.org | | Discussion | cldr-users@unicode.org | | List Email | | | URL Location | cldr.unicode.org | | Specification | Unicode Technical Standard #35 Unicode Locale | | | Data Markup Language (LDML), | | | http://unicode.org/reports/tr35/ | | Section | Section 3.2 BCP 47 Tag Conversion | +---------------+---------------------------------------------------+ The specification of extension subtags is provided by Section 3 of Unicode Technical Standard #35 Unicode Locale Data Markup Language [LDML]. As required by BCP 47, subtags follow the language tag ABNF and other rules for the formation of language tags and subtags, are Davis, et al. Expires July 17, 2010 [Page 3] Internet-Draft BCP 47 Unicode Locale Extension January 2010 restricted to the ASCII letters and digits, are not case sensitive, and do not exceed eight characters in length. [LDML] specifies a canonical representation. LDML is available over the Internet and at no cost, and is available via a royalty-free license at http://unicode.org/copyright.html. LDML is versioned, and each version of LDML is numbered, dated, and stable. Extension subtags, once defined by LDML, are never retracted or change in meaning in a substantial way. 2.1. Summary The subtags available for use in the 'u' extension consist of a set of attributes, keys, and types. Attributes, keys, types, and their respective meanings are defined in Section 3 (Unicode Language and Locale Identifiers) of [LDML]. The following is a summary of that definition (for details see Section 3): o An 'attribute' is a subtag with a length of three or more characters following the singleton and preceding any 'keyword' sequences. No attributes were defined at the time of this document's publication. o A 'keyword' is a sequence of subtags consisting of a 'key' subtag, followed by zero or more 'type' subtags. Each 'key' MUST be unique within the extension. The order of the 'type' subtags within a 'keyword' is sometimes significant to their interpretation. Note that 'keys' can appear without a subsequent 'type' subtag. A. A 'key' is a subtag with a length of exactly two characters. Each 'key' is followed by zero or more 'type' subtags. B. A 'type' is a subtag with a length of three or more characters following a key. 'Type' subtags are specific to a particular 'key' and the order of the 'type' subtags MAY be significant to the interpretation of the 'keyword'. For example, the language tag "de-DE-u-attr-co-phonebk" consists of: o The base language tag "de-DE" (German as used in Germany), exactly as defined by [BCP47] using subtags from the IANA Language Subtag Registry. o The singleton 'u', identifying this extension. o The attribute 'attr', which is an example for illustration (no attributes were defined at the time this document was published). Davis, et al. Expires July 17, 2010 [Page 4] Internet-Draft BCP 47 Unicode Locale Extension January 2010 o The keyword 'co-phonebk', consisting to the key 'co' (Collation) and the type 'phonebk' (Phonebook collation order). With successive versions of [LDML], additional attributes, keys, and types MAY be defined. Once defined, attributes, keys, and types will never be removed. Machine-readable files listing the valid attributes, keys, and types are available in the CLDR repository for each version. For example, for version 1.7.2, the files are located at http://unicode.org/repos/cldr/tags/release-1-7-2/common/bcp47/. These also can contain aliases which were used in previous versions of [LDML]. 2.1.1. Canonicalization As required by [BCP47], case is not significant. The canonical form for all subtags in the extension is lowercase. The canonical order of attributes is in [US-ASCII] order (that is, numbers before letters, with letters sorted as lowercase US-ASCII code points). The canonical order of keywords is in [US-ASCII] order by key. The order of subtags within a keyword is significant; the meaning of this extension is altered if those subtags are rearranged. Thus, the canonical form of the extension never reorders the subtags within a keyword. 2.2. Registration Form Per [RFC5646], Section 3.7: %% Identifier: u Description: Unicode Locale Comments: Subtags for the identification of language and cultural variations. Used to set behavior in locale APIs. Added: 2009-mm-dd RFC: [TBD] Authority: Unicode Consortium Contact_Email: cldr@unicode.org Mailing_List: cldr-users@unicode.org URL: http://cldr.unicode.org %% 3. Acknowledgements Thanks to John Emmons and the rest of the Unicode CLDR Technical Committee for their work in developing the BCP 47 subtags for LDML. Davis, et al. Expires July 17, 2010 [Page 5] Internet-Draft BCP 47 Unicode Locale Extension January 2010 4. IANA Considerations This document will require IANA to insert the record in Section 2.2 into the Language Extensions Registry, according to Section 3.7. Extensions and the Extensions Registry of "Tags for Identifying Languages" in [BCP47]. There might be occasional maintenance of this record. This document does not require IANA to create or maintain a new registry or otherwise impact IANA. 5. Security Considerations The security considerations for this extension are the same as those for [RFC5646] (or its successors). See Section 6. Security Considerations of [RFC5646]. 6. References 6.1. Normative References [BCP47] Davis, M., Ed., "Tags for the Identification of Language (BCP47)", September 2009. [LDML] Davis, M., "Unicode Technical Standard #35: Locale Data Markup Language (LDML)", December 2007, . [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 5646, September 2009. [US-ASCII] International Organization for Standardization, "ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.", 1991. 6.2. Informative References [ldml-registry] "Registry for Common Locale Data Repository tag elements", September 2009. Davis, et al. Expires July 17, 2010 [Page 6] Internet-Draft BCP 47 Unicode Locale Extension January 2010 Authors' Addresses Mark Davis Google Email: mark@macchiato.com Addison Phillips Lab126 Email: addison@inter-locale.com Yoshito Umaoka IBM Email: yoshito_umaoka@us.ibm.com Davis, et al. Expires July 17, 2010 [Page 7]