HTML microdata [MICRODATA] is an extension to HTML used to embed machine-readable data into HTML documents. Whereas the microdata specification describes a means of markup, the output format is JSON. This specification describes processing rules that may be used to extract RDF [RDF11-CONCEPTS] from an HTML document containing microdata.

G. Kellogg (Gregg)
W3C
Distributed and Interactive Systems

Hickson, I., Kellogg, G., Tennison, J., & Herman, I. (2014). Microdata to RDF – Second Edition: Transformation from HTML+Microdata to RDF. (G. Kellogg, Ed.).