Doug Ewell doug at
Tue Jan 21 07:21:41 CET 2014

Yes, but the set of subtags that appear in the Registry is not stable either. New subtags can be added, causing a previously invalid tag to become valid.

Section 2.2.9 again: “Note that a tag's validity depends on the date of the registry used to validate the tag. A more recent copy of the registry might contain a subtag that an older version does not.”

I’m not seeing why this applies to the presence or absence of a subtag in the Registry, but not to the encompassing language relationship. I can live with it, and will code to it, but it surprised me.

Doug Ewell | Thornton, CO, USA | @DougEwell ­

From: Mark Davis ☕ 
Sent: Monday, January 20, 2014 23:15
To: Doug Ewell 
Cc: mailto:ietf-languages at 
Subject: Re: Validity

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


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 ­ 
  Ietf-languages mailing list
  Ietf-languages at
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