// bitmask based O (1) test); where n=<number of primitives in the
// ligature> (which is typically small (n<10), though).
Stream_event *new_cause = primitive.event_cause ();
// bitmask based O (1) test); where n=<number of primitives in the
// ligature> (which is typically small (n<10), though).
Stream_event *new_cause = primitive.event_cause ();