A brief history of RDFa
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In October 2003, Mark Birbeck wrote XHTML and Metadata, which looked at whether it was possible to use RDF/XML attributes in XHTML. It also expressed some of the ideas relating to enriching the user interface, made possible by embedded semantic information.
In February 2004, Mark wrote RDF/XHTML Syntax, which took the ideas further, but removed the dependency on the RDF/XML attributes; instead, a new set of XHTML attributes was devised. (This document was also published as a W3C note, with the title XHTML and RDF.)
Another note followed later in the year, by Mark Birbeck and Steven Pemberton, this time using the name RDF/A Syntax: A collection of attributes for layering RDF on XML languages.