virtual void listen_pes_or_flexa (Stream_event *ev);
virtual void build_ligature (Spanner *ligature, vector<Grob_info> primitives);
virtual void transform_heads (Spanner *ligature,
virtual void listen_pes_or_flexa (Stream_event *ev);
virtual void build_ligature (Spanner *ligature, vector<Grob_info> primitives);
virtual void transform_heads (Spanner *ligature,