Comment:

Value set not required to have compose or expand: ok, but we need a way to clarify which is being requested or supplied.

"The ValueSet resource can carry either the .compose or the .expansion, or both." - update to include neither.

On retrieval, it's not exactly content negotiation, but you might want a) metadata only, b) definition, c) expansion, d) all three. (and maybe e: expansion only)

Summary:

Allow Value set to have neither compose nor expand