java is not html nor governed by W3C.
PhP is not html nor governed by W3C.
SQL is not html nor governed by W3C.
SVG is not html nor governed by W3C.
FLASH Generated Site is not html nor governed by W3C.

Strict adherence to XML, HTML is a pipe dream and will always be ignored by innovators.

Making a Web page is an individual issue unless you work for some company or client that requires strict compliance.

If you are not restricted by employment, W3C is just three letters that is mostly meaningless to most people who do Web Work.