I have a question. Why do we have to use media types here? If an XML
document contains a link which takes advantage of XPointer, we just know
that the URI references to an XML document and thus do not have to be
notified by XML media types.
This is dangerous; you would be limiting the applicability of
XPointer to only work with XML. What if someone were to invent,
oh, a "binary XML". (There are several efforts to do so.) XPointer
references might just as well apply to binary XML.
Would it be possible to extend XPointer to work with Zip files
which contained XML files, so that you could point into an XML
document that was stored inside a ZIP file?
Then you wouldn't know that "the URI references to an XML document".
Restricting XPointer only to work with XML would be limiting it
unnecessarily.
The ability to do generic XML linking into internal body parts
of XML-encoded data might be a reason for calling out XML-specific
media types, especially if XML documents are "compound" and the
media type used just indicates the "top level".
So far, this is the first example that resonates with me,
although it might be that "application/xml" is good enough
for all of these examples, with a separate content-disposition
or content-features for calling out either the intention
for how the sender might want the information processed by
the recipient, or some indication as to the namespaces or
other content features of the XML body.
Larry