Reported by Bertilo Wennergren:

It would perhaps be a good idea if the validator reported the media type
of the validated resource. The choice between "text/html",
"application/xhtml+xml", "application/xml" (and whatever else) for XHTML
docs, is an important issue that many people are not even aware of.

The new validator should probably also report what character encoding it
detected (the old one does).