IMO: HTML isn't the best choice if you are interested in anything.
This obsolete format should not be considered if even mentioned. Use XHTML + CSS instead, if you are allergic to XML.
XHTML is HTML 4.0 designed to work as an XML application. In fact, there aren't a lot of differences between HTML and XHTML. Of course, XHTML, HTML, and XML are all "children" of SGML anyway, so we're all talking about generalized markup in some form or another. You can't set up a rigid set of rules that will apply across all past, present and future versions of printed works in electronic format. Whatever format you choose to use, must be extensible enough to scale for future capabilities, as well as the ability to handle the capabilities of documents created in the past.
With properly written XHTML and customizable CSS user can do what ever he wishes with the files and the things are still as they should be.
Almost whatever s/he wishes. There are limitations in every format, depending on how broadly you want to consider using it. David A. Desrosiers desrod@gnu-designs.com http://gnu-designs.com