Browsers (and some OS) have a way to assiciate MIME types with applications.
Catalogs need to be a distributable format for this.
One of the decisions of the text/xml RFC is that it should work on an entity
basis: it refers to a single entity, and NOT a complete document.
In SGML there has been a long bunfight about MIME media types: both the
camps have the view that whole documents should be sent, but one camp wants
the types to only send entities which are actually used (for size
minimisation) while the other side wants to leave that up to the sender. So
for text/xml the WG wisely abandoned the idea of sending compound documents.
But this does mean that questions about bundling catalogs are not answered.
I think XML-DEV should similarly avoid the bundling question (it is more
applicable to sending documents by email anyway). It should define a
standard notation to allow embedded Catalogs in a PI. The PI should go as
far towards the head of the document as possible. Of course, an external
resource is OK too, but an internal PI saves a download.
<?xcat
...
?>
Rick Jelliffe