The pipeline could now keep only where two selections agree, but the panel
had no way to ask for it: the part row's chip flipped between + and -, and
the buttons under the parts joined an added or a subtracted correction.
An "∩ Intersect" button joins a painted part that intersects, and the chip
on a part row cycles + -> - -> ∩ and round, so an existing part can be
turned into an intersection without being repainted. Both go through the
same session calls as before, indexing Join::ALL, whose first two entries
kept their places. The chip is now a tagged gesture, so it is in the
gesture book.
dtourolle
5f0b7ac799