RDFa is a way of embedding RDF in HTML that has maybe one or a few publishers on the indieweb, but no known consuming use-cases, perhaps due to being unnecessarily more verbose than Microformats as demonstrated by the example documented at kevinmarks.com/microformatschema.html.
RDFa adds several attributes to standard HTML:
typeof to specify an RDF resource type,
vocab to specify the schema containing the type, and (much more plentifully)
property to specify the field names described by markup nodes. Microformats use the already existing
class attribute for all these purposes, following common Semantic HTML practices.