http://www.sandia.gov/sci_compute/html_ref.html
It tells you if tags are valid HTML 2.0, 3.0 or non-standard Netscape
extensions -- it also does a great job of showing what tags are allowed
inside other tags.
-Matt
Matt Ericson
mericson@icaen.uiowa.edu
http://www.icaen.uiowa.edu/~mericson/