The W3C Semantic Web Deployment Working Group and XHTML2 Working Group jointly published the First Public Working Draft of RDFa in XHTML: Syntax and Processing. RDFa attributes can be used with languages such as HTML and XHTML to express structured data. RDFa allows terms from multiple independently-developed vocabularies to be freely intermixed. This document has parsing rules for those creating an RDFa parser as well as guidelines for users in organizations who wish to use RDFa. For those who would like start using RDFa, the RDFa Primer is an introduction to its use and shows real-world examples.