The caret's current function context.
OptionalshowRender the stacked argument list under the summary.
false leaves just the summary — the shape a BROWSING surface wants (the Insert Function
dialog's function list, where the signature above already says what the arguments are and the
per-argument prose belongs to the next step). While EDITING, the argument list is the point of
the panel, so the editor leaves this alone.
The lazily-loaded descriptor text, or
nulluntil it resolves (or if it fails).