The HTML+ DTD permits infinite nesting, but people are unlikely to want
more than about three levels in practice. Browsers must cater for more
though with a graceful degradation for deeply nested lists.
> Once a decision is made on this I suppose it needs to be written
> into the spec. (If nested lists ever make it in)
The HTML DTD formally prohibits nested lists.
(see http://info.cern.ch/hypertext/WWW/MarkUp/HTML.dtd.html)
Dave Raggett