Edit: Boy, do I feel stupid. What I proposed exists, and is called RDFa. (http://www.w3.org/TR/rdfa-syntax/ http://www.w3.org/TR/rdfa-syntax/) It occurs to me

Edit: Boy, do I feel stupid. What I proposed exists, and is called RDFa. (http://www.w3.org/TR/rdfa-syntax/ http://www.w3.org/TR/rdfa-syntax/) It occurs to me that the W3C already has an extensible semantics framework: RDF. This framework can be represented in many different languages (primarily N3 and XML), and is quite well-understood amongst semantic web people. The trouble is how to associate RDF 3-tuples with (X)HTML elements. To take the date example from the original article, <span id="date1">May Day next year</span> could be represented in a machine readable format be the following 3-tuple. (I am not an expert in N3, so please pardon any mistakes. Also, if there's a good existing vocabulary for "equivalent to", please let me know.) <#date1> <http://example.com/#equivalent&#62 http://example.com/#equivalent> date"2009-05-01" In turn, this 3-tuple could be encoded in <meta> and <link> elements a la Dublin Core, or could be stored in an external RDF/XML or N3 document referenced by a <link> element. Perhaps a new element could even be introduced (just one) that allows the direct embedding of RDF content in a manner similar to the embedding of CSS content via the <style> element. This solution would have the benefits of being extensible, flexible, robust and well-understood. The biggest drawback that I can see is that developers would have to learn RDF along with some common ontologies.