RDF readers.
See: - [http://www.w3.org/TR/rdf-sparql-XMLres/](Sparql Query Results XML Format) - [http://www.w3.org/TR/rdf-sparql-json-res/](Sparql Query Results in JSON)
the type of object that this Writer can serialize
the Syntax that this Writer supports
RDF readers.
All functions return results in the context
M
.S
is a phantom type for the syntax.