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.
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.
I tend to lean towards "every application gets a new media type".
--Paul Hoffman, Director
--Internet Mail Consortium