The importer kept a group's isolation only when something inside it
blended, so an isolated group or knockout group whose objects only
overprint read back without isolation. Written out again, it lost its
/I true and its overprinting objects then kept the inks of the art below
the group that they had covered. Isolation is now also kept when a
visible fill or stroke inside, or characters' fill or stroke, overprints,
directly or through children that do not isolate.