json-ld-syntax review, part 2

I think the document could be greatly strengthened (and most of my 
non-trivial comments in part 1 addressed) by the following changes: \

1.  In Conformance add something like:

    A conforming */JSON-LD Expander /*takes as input a conforming
    JSON-LD document D1 and outputs a conforming JSON-LD document  D2,
    using the expansion mapping defined in Appendix @@1.  D2 will
    contain no @context declarations and, informally, will convey the
    same underlying information.

    A conforming /*JSON-LD Compactor*/ takes as input a JSON-LD @context
    declaration and conforming JSON-LD document D2 and outputs a
    conforming JSON-LD document D1, such that a conforming JSON-LD
    Expander would convert D1 to D2 (or an equivalent document which
    would JSON-parse to the same internal structure).

    A conforming /*JSON-LD To-RDF Converter*/ takes as input a
    conforming JSON-LD document J and outputs an RDF Dataset R using the
    conversion mapping defined in Appendix C.

    A conforming /*JSON-LD From-RDF Converter*/ takes as input an RDF
    Dataset R and output a JSON-LD document J such that a conforming
    JSON-LD To-RDF Converter would convert J to D (or an equivalent
    document which would JSON-parse to the same internal structure).

Note there is no need to define the Compaction and From-RDF mappings in 
detail; it's enough to say (as above) that they are the inverses of 
already-defined mappings.   I believe that sufficiently constrains 
them.  For implementation advice, they can see another document, which 
need only be a Note.

2.  Add appendix @@1 which defines the expansion mapping.     I have not 
actually looked at how that's currently defined.

3.  Move json-ld-api sections 5.18-5.21 and 5.23 to json-ld-syntax 
appendix C.

Note that we should probably change the shortname from 
/TR/json-ld-syntax to /TR/json-ld for the next publication.  It's a bit 
of a pain, but worthwhile in the long run, I think.

These changes would make json-ld-syntax stand parallel to Turtle, as a 
completely defined RDF serialization syntax (not *needing* the API 
document), but they wouldn't significantly reduce the "RDF tax" on 
JSON-LD.   Just a few sentences in Conformance and a longer RDF 
Appendex.  That seems to me like a good thing (and also what I 
understood the RDF WG to be asking for).

      -- Sandro