Kind of two related bugs here, both seen when trying to validate a XHTML
document sent as text/html with has a buggy doctype declaration, eg. "!doctype"
in lowercase.

First, the fallback in sgml.soc:

  DOCTYPE html REC-html401-19991224/loose.dtd

This causes confusion because there is nothing in the output that would indicate
that a doctype wasn't found and that such a fallback is being used.  Something
should be done to this, maybe removed altogether if a better alternative is not
found.

Second, if the above fallback is removed, validator still doesn't recognize the
doctype (due to lowercase doctype declaration and HTML::Parser's xml_mode) but
goes on to validate using sgml.soc and SGML rules (so onsgmls will retrieve the
online XHTML DTD but will not emit a AVERSION...), and says "This document is
not Valid !" but does not mention that it did not properly recognize the
document type.