MultiMarkdown is a special syntax that is used to make the sources of static web pages more human readable, and its is also more pleasant to write in than HTML. The multimarkdown processor script, usually Perl or Python, will convert the MultiMarkdown document to HTML before it's published. It would be nice to see TclHTTPd support MultiMarkdown too.
Here's more information on Markdown: http://daringfireball.net/projects/markdown/
Philosophically speaking, this doesn't appear to be any different than all the various wiki formatting languages.