Re: Limitations on JSON which conforms to JSON-LD spec?

Sure, @index lets you know... something. cardinality, maybe.

{
>   "@context":{
>     "npm": "https://www.npmjs.org/doc/files/package.json.html#",
>     "dependencies": {
>       "@container": "@index",
>       "@id": "npm:dependencies"
>     }
>   },
>   "dependencies": {
>     "jsonld.js": "^0.3.13"
>   }
> }
>

normalizes to:

_:c14n0 <https://www.npmjs.org/doc/files/package.json.html#dependencies>
> "0.3.13" .
>

not very instructive, and the @index value disappears.

if you were advising a new developer on patterns to not use, that would be
one of them!