ADD_END_ACKNOWLEDGER (Spanner_break_forbid_engraver, unbreakable_spanner);
ADD_ACKNOWLEDGER (Spanner_break_forbid_engraver, unbreakable_spanner);
ADD_TRANSLATOR (Spanner_break_forbid_engraver,
ADD_END_ACKNOWLEDGER (Spanner_break_forbid_engraver, unbreakable_spanner);
ADD_ACKNOWLEDGER (Spanner_break_forbid_engraver, unbreakable_spanner);
ADD_TRANSLATOR (Spanner_break_forbid_engraver,