Language subtag registration for acor1990 (ammended from ao1990)

[Stephane Bortzmeyer]

On Thu, Aug 25, 2011 at 02:49:38PM +0100,
 António H F P A Emiliano (FCSH/UNL) <ah.emiliano at fcsh.unl.pt> wrote 
 a message of 161 lines which said:

> iii) can anyone please direct me to a document that states the
> formal requirements of a language subtag of this kind?

<http://www.w3.org/International/articles/language-tags/> is a good
start on language
tags. <http://en.wikipedia.org/wiki/IETF_language_code> is good,
too. <http://www.langtag.net/register-new-subtag.html> is a primer on
the registration of new subtags. If you want the full standard
(warning: not for the faint of heart),
<http://www.rfc-editor.org/rfc/rfc5646.txt>.