I've seen it adressed with and additional parameter ?field=list,of,those,you,want in a few big commercial applications. It did not file REST-way to me, but it is easy and works both server- and client-side.
Sure. And then you also want to query subfields, you can extend your query parameter list with some specific scheme for that (e.g. `subfields=fieldX.subfieldX,fieldY.subfieldY` - and then you can enhance it with filters, mutations, recursion, introspection, types, documentation, deprecation features... and then you have built your own version of graphQL.
At some point, it is better to leave the custom solution field and go for graphQL before rebuilding it.
