Field selection
GET /books?select=id,titleselect picks a sparse fieldset for the root resource, validated against the select.fields allowlist. Narrow an included relation the same way: select[author]=id,name.
select.fields also decides what a response carries when no select= is sent — unless the entity configures select.default, a narrower default projection applied only when the request sends no select= of its own (a client-supplied select= always wins outright, same as sort.default). select.fields is the one place to keep a column out of every response, regardless of select.default. A registered class-shaped output schema with a runtime shape (schema.output.item/list, or an operation's own schema.output) caps select.default the same way: a default field the schema omits is dropped, never served, and a default that shares no field with it fails at bootstrap. A server-side select.apply (Apply) is unioned into select.default when no select= is sent, so its forced fields are served alongside the default, still bounded by select.fields and any class-shaped output schema. See Allowed and Config keys.