?attribute= narrows it to one attribute's sets. A matter names the sets that apply to it and never owns options of its own, which is what keeps one list in one place however many matters read it. Where the firm's practice system shows each person their own matters, a set of the system's that only matters the caller is not shown name is left out.

Operator mount: an operator acting for the firm named in the path, as its oldest active admin, else its oldest active billing member; X-Six-Minute-Acting-As names them. 404 for no such firm, 409 urn:six-minute:problem:no-acting-member for one with neither.