BCP 47 Extension U

Language tags, as defined by , 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 List Email cldr-users@unicode.org 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. As required by BCP 47, subtags follow the language tag ABNF and other rules for the formation of language tags and subtags, are restricted to the ASCII letters and digits, are not case sensitive, and do not exceed eight characters in length. 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.

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 . The following is a summary of that definition (for details see Section 3):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.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 'key' is a subtag with a length of exactly two characters. Each 'key' is followed by zero or more 'type' subtags. 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:The base language tag "de-DE" (German as used in Germany), exactly as defined by using subtags from the IANA Language Subtag Registry.The singleton 'u', identifying this extension.The attribute 'attr', which is an example for illustration (no attributes were defined at the time this document was published).The keyword 'co-phonebk', consisting to the key 'co' (Collation) and the type 'phonebk' (Phonebook collation order).With successive versions of , 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 .

As required by , case is not significant. The canonical form for all subtags in the extension is lowercase. The canonical order of attributes is in order (that is, numbers before letters, with letters sorted as lowercase US-ASCII code points). The canonical order of keywords is in 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.

Per , 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 %%