+ SCM p = nr->get_property ("pitch");
+ /*
+ If the engraver is added to a percussion context,
+ filter out unpitched note heads.
+ */
+ if (!unsmob_pitch (p))
+ return;
+ Pitch pitch = *unsmob_pitch (p);
+ Drul_array<bool> expands = pitch_interval_.add_point (pitch);
+ if (expands[UP])
+ causes_[UP] = nr;
+ if (expands[DOWN])
+ causes_[DOWN] = nr;