Mark Davis ☕ mark at
Tue Jan 21 07:15:22 CET 2014

That's on purpose, since the encompassing language relationship is not

On Jan 21, 2014 6:48 AM, "Doug Ewell" <doug at> wrote:

> 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
> | @DougEwell ­
> _______________________________________________
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> Ietf-languages at
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