Intl::LanguageTaggish

A role to be implemented by different representations of a language/locale identifier. It provides for the following three methods/attributes:

• language
  The language, generally in ISO 639 format (as either a Str or something that coerces accordingly)
• region
  The region, generally in ISO 3166/UN M.49 format (as either a Str or something that coerces accordingly)
• bcp47
  A BCP-47 representation of the tag, to the extent possible (as a Str). May be lossy.

Raison d’être

While there are not many language tag standards, there are several in common use. This role aims to define some common features to aid their interaction.

A bcp47 method should provide conversion into a BCP-47-compliant string. For example, Apple allows "English" or "Spanish" as valid identifiers for its .lproj identifiers. So a theoretical AppleLProj class that does LanguageTaggish would output English for .language, but for bcp47, would output en.

It is expected that class implementing LanguageTaggish will add additional methods and attributes. In keeping with tradition established by other language tag frameworks (in particular ICU), requested values not present should return the empty string.
The role handles this by default via its FALLBACK method.

In addition, each LanguageTaggish implementor is expected to also provide a method `

Coercions into LanguageTaggish

Classes implementing LanguageTaggish register themselves on the first use statement to be available for coercion. Optimally, programmers in international environments will know what tag is needed, however, when it's not possible, the COERCE method aims to do its best. In priority order, classes judge whether they can handle the tag, and if so, will do the coercion. This approach is not (as of v0.1) finalized and may be adjusted.

• Intl::LanguageTag::BCP-47 (:100priority)
  This IETF BCP-47 representation (uses hyphens and subtags are limited to 8 characters).
• Intl::LanguageTag::Unicode (:75priority)
  The Unicode language tag standard (uses underscores generally, subtags may have any number of characters)
• Intl::LanguageTag::POSIX (:50priority)
  The standard langauge tag as used in POSIX (underscores, at symbols, and dots may delineate subtags)
• Intl::LanguageTag::UnicodeLegacy (:25priority)
  The legacy style Unicode langauge tag (underscores and at symbols delineate subtags, special characters like slash are valid as variant values)
• Intl::LanguageTaggish::Fallback (:0priority)
  A fallback that detects the first (and possible second) sequence of alpha characters as the language (and possible region).

Note that if you use Intl::LanguageTag, you will get the BCP-47 implementation, as it is currently the most common format.