My only suggestion, for what it's worth, would be to allow for the
declaration (and please don't overinterpret that word ;-) ) of the 'root'
namespace for a document. That seems a reasonable distinction to make,
I am not convinced. In the case of XSLT, the root of an XSLT
stylesheet do not always belong to the XSLT namespace. Why is the
top-level namespace so important?
although you'd then have to define how such a statement interacts with
content-type declarations such as application/xml+mathml (would that, in
some twisted way, imply a default 'root'-level namespace, and if so,
how?).
I think that this is a good reason NOT to introduce special
handling of the top-level namespace.
Cheers,
Makoto