I co-organized the Web2.0 conference track that was held at Solutions Linux 2007 in Paris last week . Researching to prepare the talk I gave, I came accross microformats and GRDDL. Both try to add semantics on top of (X)HTML.Microformats uses the class attribute and the "invisibility" of `div` and `span` to insert semantic information, as in ::
<li class="vevent"> <a class="url" href="http://www.solutionslinux.fr/"> <span class="summary">Solutions Linux Web 2.0 Conference</span>: <abbr class="dtstart" title="20070201T143000Z">February 1st 2:30pm</abbr>- <abbr class="dtend" title="20070201T18000Z">6pm</abbr>, at the <span class="location">CNIT, La Défense</span> </a> </li>
GRDDL information is added to the `head` of the XHTML page and points to an XSL that can extract the information from the page and output it as RDF.
Another option is to add `link` to the `head` of the page, pointing to an alternate representations like a RDF formatted one.