I think instead you should check out
<URL:http://www.eit.com/projects/s-http/> - I honestly feel that this
kind of information should be dealt with external to the HTML document
itself, because a solution that works like that will also work for any
kind of datatype.
There is a good intro to SGML principles at
ftp://www.ucc.ie/pub/sgml/p2sg.ps
///Peter