Officially now a 'web-standard', RDFa is the implementation for writing RDF statements inline to a XHTML document using 9 specific attributes.
4 of these are supported in XHTML 1.0
The other five are specific to XHTML+RDFa 1.0, so your document will have to conform to the DTD.
- about
- property
- resource
- datatype
- typeof