[html4all.org] Content-type negotiation as an alternative to ALT, LONGDESC and fallback

[Philip TAYLOR]

Before I float this on the main list, I'd like to bounce
it off "the advocates group", where it may receive a more
open-minded review :

Although we have already agreed that HTML itself needs
to provide fallback (because media authors may not have
done so intrinsically), I now begin to wonder whether the
whole ALT/LONGDESC/fallback issue is not better addressed
at the HTTP level.  Given that HTTP already supports
content-type negotiation, is it conceivable that we
could make use of this by specifying that embedded
content should not use explicit MIME type or filename
extensions ?  A page could then make reference to
(say) <img src="Australian-flag"> and if the user's
browser were set to prefer (say) "audio/*" over "text/*"
over "image/*" (and if <img> were re-defined in HTML 5
to accept any MIME type, not just images), then the
user would receive an audio description of the flag
if available, then as first fallback a textual description,
and finally -- if and only if neither of the others
were available -- the image itself.

What do others think ?

** Phil.