AgentZombie commented :
Sorry. I was speaking specifically about the graph label field in RDF n-quads. dgraph specifically reads RDF n-quads as a superset of n-triples but doesn’t use the fourth value to specify a named graph.
From RDF 1.1 N-Quads
The simplest statement is a sequence of (subject, predicate, object) terms forming an RDF triple and an optional blank node label or IRI labeling what graph in a dataset the triple belongs to, all are separated by whitespace and terminated by ‘.’ after each statement.
This was referenced here, #1143, and probably other places.