Originally Posted by user_none
EPUB does have a standard and uses XHTML. To be a valid EPUB the HTML should be valid XHTML. ...
Yes, that is well and good for ePub output but validating "HTML" is not validating "XHTML" and, my major point, not all that usefull in creating a file for the purposes of converting to MOBI. The EPUB validation standards don't apply to HTML code written for conversion to MOBI.