+ void substitute_one_mutable_property (SCM sym, SCM val);
+ bool fast_fubstitute_grob_list (SCM sym, SCM grob_list);
+ // TODO: make virtual and do this for Items as well.
+ Interval_t<int> spanned_rank_iv ();
+ void set_bound (Direction d, Grob *);
+ Item *get_bound (Direction d) const;
+
+ Spanner (SCM, Object_key const *);
+ Spanner (Spanner const &, int copy_count);
+ bool is_broken () const;
+ void do_break ();
+ Real spanner_length () const;