hypothetical Cajun question

[Sean M. Burke]

A procedural question:

Suppose (just hypothetically) that I want to tag some documents that are in 
(Louisiana) Cajun French.  Not Louisiana French Creole (the other end of 
the dialect continuum), but Cajun.
A fairly obvious tag choice is "fr-us-la".

My question is: I don't think that that /has/ to be registered with 
IANA.  But /can/ it be registered?
I'm under the impression that besides establishing i-foo tags, the IANA 
language tag registry also has some (possibly "secondary") role as a place 
to say "among all the possible ways that you might imagine to express a 
language tag for Cajun, this is the one that we think people should use."
But I emphasize that this is just an impression on my part.

--
Sean M. Burke    http://www.spinn.net/~sburke/