> [Original Message]
> From: Christian Wolfgang Hujer <Christian.Hujer@itcqis.com>
>
> Annotation:
> > I for my part suggest multiplication of q values and rounding them with
> > round5, similar as described in RFC 2295 Appendix 19.1
> > Such a note should take into account RFC 2616 and RFC 2295, especially
the
> > 406 response.
> Of course that requires that the user agent will not use a default
quality of 
> 0.0 but a different one.

It is isn't supposed to anyway.  From RFC 2616 Section 14.4:
   As intelligibility is highly dependent on the individual user, it is
   recommended that client applications make the choice of linguistic
   preference available to the user. If the choice is not made
   available, then the Accept-Language header field MUST NOT be given in
   the request.

So in other words, if a language has its user q-value set to 0,
this is the result of a conscious choice on the part of the user.
To have an XHTML attribute allow an author to override
a deliberate user choice is not good practice.