Definition of Unicode Locale

[r12a]

https://w3c.github.io/ltli/#ref-for-dfn-unicode-locale-1

Unicode Locale Identifier or Unicode Locale. A language tag that follows the additional processing rules defined by [CLDR] in UTR#35 [LDML]. A Unicode Locale can include a combination of certain language tag extensions ([RFC6067], [RFC6497]), although it is not required to do so.

A Unicode locale provides the ability to specify in a language tag some international preference variations that go beyond linguistic or regional variation or to select formatting behavior or content when there are multiple options or user preferences within a given locale. Unicode locale identifiers are well-formed [BCP47] language tags. [CLDR] also specifies some additional rules about the structure and content of the Unicode Locale's language tag as well as supplying specific interpretation of certain subtags. See Section 3.2 of [LDML] for details.

Unicode's [CLDR] project maintains both of the [BCP47] extensions related to Unicode locales. The Unicode locale language tag extension [RFC6067] uses the -u- subtag, and provides subtags for selecting different locale-based formats and behaviors. See Section 3.6 of [LDML] for details.

The Transformed Content extension [RFC6497], which uses the -t- subtag, provides subtags for text transformations, such as transliteration between scripts. See Section 3.7 of [LDML] for details.

Unicode Locales increasingly form the basis for internationalization on the Web, particularly as part of the Intl locale framework [ECMA-402] in JavaScript [ECMASCRIPT].

This appears to me to say that language tags without -u or -t extensions are not Unicode Locale identifiers, and therefore not suitable for locale identification. It then goes on to say that

Content authors SHOULD choose language tags that are canonical Unicode locale identifiers.

and

​Implementations SHOULD only emit language tags that are canonical Unicode locale identifiers ...

Which to me implies that any time anyone uses a language tag, it should include -u and/or -t tags. Which doesn't sound right.

It seems to me that the definition is problematic, and could be changed to say one of the following (i'm being deliberately open here to possibilities):

1. A language tag that follows the LDML rules and includes a canonical unicode locale identifier (ie. -u or -t) can be referred to as a unicode locale identifier.
2. The part of a language tag that includes -u and/or -t and the subtags that follow them is referred to as a unicode locale identifier.

Whichever is chosen, i think the mustard needs to be crafted way that is a little more subtle.

Btw, it may be useful to briefly expand on "the additional processing rules defined by [CLDR] in UTR#35 [LDML]."

[aphillips]

A Unicode Locale can include a combination of certain language tag extensions ([RFC6067], [RFC6497]), although it is not required to do so.

The need to introduce the extensions may swamp that message, but it's important to note that several specifications (most importantly ECMA-402) have adopted Unicode locale identifiers as a term. It's the rules, not the extensions, that are important in most cases.

As usual, you make a good point about the visibility of the text I emphasized above. You have to read all the way past the next definition and the mustard to reach:

It is important to remember that every Unicode locale identifier is also a well-formed [BCP47] language tag.

... and this still fails to emphasize that most language tags are good enough without extensions. The extensions exist to provide finer tailoring if and only if the user needs it.

Perhaps split this bit of text off the second paragraph quoted above to emphasize it?

Unicode locale identifiers are well-formed [BCP47] language tags. [CLDR] also specifies some additional rules about the structure and content of the Unicode Locale's language tag as well as supplying specific interpretation of certain subtags. See Section 3.2 of [LDML] for details.

I think we could then clear up the confusion by adding one more mustard item with explanation:

Content authors SHOULD NOT include extensions in their language tags unless their specific application requires the additional tailoring.

Unicode locale identifiers do not require the -u- or -t- extensions. These should only be used when the subtags in them are actually needed by the application.