Validity

[Doug Ewell]

One of the readily available test suites for BCP 47 tags shows "fr-fra" 
and "fr-Lat" as valid tags. They aren't, of course, because Section 
2.2.9 says:

> A tag is considered "valid" if it satisfies these conditions:
>
> o  The tag is well-formed.
>
> o  Either the tag is in the list of grandfathered tags or all of its
>    primary language, extended language, script, region, and variant
>    subtags appear in the IANA Language Subtag Registry as of the
>    particular registry date.
>
> o  There are no duplicate variant subtags.
>
> o  There are no duplicate singleton (extension) subtags.

and the extended language subtags 'fra' and 'lat' do not appear in the 
Registry (nor could they ever).

I was surprised, however, to see that a combination of language and 
extlang subtags that don't match -- that is, the language is not the 
Prefix for the extlang, as "ar-cmn" -- is perfectly valid. In fact, the 
language subtag in such a pair doesn't even have to have its own 
extlangs, so one could also write "fr-cmn" or "tlh-cmn" and a validating 
processor would have to accept them. Does this surprise anyone else?

--
Doug Ewell | Thornton, CO, USA
http://ewellic.org | @DougEwell ­