It's not clear that specialized media types solve any problem at all,
in the case of XML that already contains a document declaration.
The overhead of having to open up every XML document to find out what
document type it is is not practical. As in the case of email, all I should
have to do is ask for a particular type of object from the store and get it.
In addition, though, we also want to get at subtypes of objects. Or in the
case of MIME type/subtypes, this would be the "sub-sub type". For example,
for a calendar object (text/calendar) we want to pull to the client just the
"event invitations". This would be the "sub sub type" of type=text,
subtype=calendar.
- - Frank