From: "LeVan,Ralph" <[log in to unmask]>
>And, yes, application/sru+xml is unofficial, as are application/m21+xml and 
>application/Unicode+xml that I also support.

Now that's a bit misleading as it seems to equate application/sru+xml  with 
application/m21+xml and application/Unicode+xml.

As far as I know there is no application registration for the latter two 
(correct me if I am mistaken).  application/sru+xml WILL become an official 
media type, it's a matter of getting past the horrendous IETF bureucracy, 
they still live in the 20th century (actually, more like the 70s).
But we're working on it, making some progress.
--Ray