@default in JSON-LD API

In [1] there are a lot of @default mentions (subsections: 9.1, 9.2, 
10.1, 10.4). @default is not defined in [2]. It is only defined in [3] 
but in [1] there is no reference to [3]. I think adding reference is a 
minimum plan.

It is pretty annoying that in algorithms there is @default keyword which 
is not a part of recommendations. And there is no information what it is.

[1] http://www.w3.org/TR/json-ld-api/
[2] http://www.w3.org/TR/json-ld/
[3] http://json-ld.org/spec/latest/json-ld-framing/

Best,
Dominik Tomaszuk