RDFa Vocabulary for Term and Prefix Assignment, and for Processor Graph Reporting
RDFa Core is a specification for attributes to express structured data in any markup language. The embedded data already available in the markup language (e.g., HTML) can often be reused by the RDFa markup, so that publishers don't need to repeat significant data in the document content. (from https://www.w3.org/TR/rdfa-core/)