Dispatching based on media types raises a few important issues that are
somewhat unique to XML.
If we say "every application gets a new media type" then there is no clean
way for a MIME-handling application to fall back to handing an unknown
media type to an XML parser. An unclean way for such an application to
handle an unknown media type is to look inside the first few octets of the
body and, if it looks like XML, hand it off to the XML parser instead of
treating it as application/octet-stream or text/plain.
If we say "stick everything XMLish under a media type that is XML-specific
with some parameter for the kind of XML" then we assume that handing off
unknown body types to an XML parser is useful. I question this assumption.
And I agree. While I have no strong objection to creating a special top-level
type for XML-based things, what experience has shown is that fallback
strategies of *any* sort tend to be overrated. In almost every case something
has messed it up. Either we got the granularity wrong (and I see a very good
chance of this happening here given the emergence of alternative forms of XML),
or it didn't prove to offer useful functionality, or it simply didn't deploy in
the manner in which we envisioned. About the only success story we have,
actually, are the image/audio/video top-level types, and while these have
worked out tolerably well, their actual value to end users isn't that great.
What's the XML parser going to do with this block of data? Display it? Not
terribly valuable. Get some namespace information from the inside and then
dispatch based on the namespace? Possibly valuable, but this begs the
question of why wasn't that information out in the MIME headers.
It is valuable in the case of a developer who wants to fire up an XML editing
tool. But let's be real here -- such a person had better be perfectly capable
of assigning types to their editor. If they cannot they had best look for
a new line of work.
I tend to lean towards "every application gets a new media type".
In case it isn't obvious by now, so do I.
Ned