Specify a node type when interpreting JSON as JSON-LD (was: use of "@type" in "@context")

Question

It's not clear to me if it's legitimate to use @type in @context instead of in the JSON object, eg.

"@context":
  "@vocab": "https://schema.org/",
  birthplace:
    "@type": "City"
birthplace:
  name: Roma

since the jsonld playground renders this as

_:c14n0 <https://schema.org/birthplace> _:c14n1 .
_:c14n1 <https://schema.org/name> "Roma" .

while I expect

_:c14n0 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <https://schema.org/City> .
_:c14n0 <https://schema.org/name> "Roma" .
_:c14n1 <https://schema.org/birthplace> _:c14n0 .

Note

changing the payload to

"birthplace": "Roma"

results in

_:c14n0 <https://schema.org/birthplace> "Roma"^^<https://schema.org/City> .

meaning that in some way the "City" type is processed in some way.

Start by reviewing the JSON-LD 1.1 specification and the JSON-LD Playground behavior shown in the issue. Compare the two supplied JSON-LD examples and their resulting RDF, then determine whether the specification needs clarification or a correction. Done means the expected interpretation is resolved and the specification or examples clearly document it.