Clarify prefix expansion about json-ld.org

[lanthaler]

Gregg's suggestion:

It should say "concatentating the prefix and suffix separated by a colon (:)." If a key matches a production containing NCNAME ':' followed by anything else, and the NCNAME portion (prefix) matches a defined term, the prefix ':' combination is replaced by the value of the term definition. In these examples, you should get the following:

<> <http://example.com/payment/payment> "done" .
<> <http://example.com/payment/amount> "20.4"^^xsd:double .

The only portion of the key subject to term replacement is the prefix, everything after the colon is used without performing any substitution.

[lanthaler]

This is now well described In the latest version of the API spec but we might wanna include some of the details as well in the syntax spec.

[gkellogg]

I tried to make more explicit how terms and prefix:suffix are expanded in the IRIs section of Basic Concepts. If you think this is now clear enough, please mark the issue as closed, and this will complete my action item from the last call.

[msporny]

http://json-ld.org/spec/ED/json-ld-syntax/20120122/#the-context

http://json-ld.org/spec/ED/json-ld-syntax/20120122/#prefixes

http://json-ld.org/spec/ED/json-ld-syntax/20120122/#iri-expansion-within-a-context