How many arguments a name takes, checked against the call as written. A signal is
positional, a required parameter is answered once, and an unread key is refused.
The one producer of the three-part shape of FORMAT 7.1 and the operand-then-repair shape
of 8.3: every code of section 16 reaches a diagnostic through here.
Every operand in the order written. Ty has no scalar of its own, so a constant arrives
as the representation of the signal it meets, neutral by FORMAT 3.3’s Sc, S -> S row,
under its own width.