I see reference to it here: https://w3c.github.io/json-ld-syntax/#the-rdf-json-datatype but can't track down any mention in what I think are the relevant sections in the RDF or RDFS recs https://www.w3.org/TR/rdf11-concepts/#section-Datatypes https://www.w3.org/TR/rdf-schema/#ch_literal