Description
Currently the HtmlParser will try to resolve usemap and codebase attributes in elements.
usemap is actually not a URI - see http://ln.hixie.ch/?start=1172653243&count=1 for a lengthy description of why the DTD at http://www.w3.org/TR/2002/REC-xhtml1-20020801/dtds.html#a_dtd_XHTML-1.0-Strict is incorrect.
codebase is actually a base URI that's used to resolve other relative URLs for <object> and <applet> elements.