+
+void
+Spanner::derived_mark () const
+{
+ Direction d = LEFT;
+ do
+ if (spanned_drul_[d])
+ scm_gc_mark (spanned_drul_[d]->self_scm ());
+ while (flip (&d) != LEFT)
+ ;
+
+ for (vsize i = broken_intos_.size (); i--;)
+ scm_gc_mark (broken_intos_[i]->self_scm ());
+}
+
+/*
+ Set left or right bound to IT.
+
+ Warning: caller should ensure that subsequent calls put in ITems
+ that are left-to-right ordered.
+*/
+void
+add_bound_item (Spanner *sp, Grob *it)
+{
+ if (!sp->get_bound (LEFT))
+ sp->set_bound (LEFT, it);
+ else
+ sp->set_bound (RIGHT, it);
+}
+
+MAKE_SCHEME_CALLBACK (Spanner, set_spacing_rods, 1);
+SCM
+Spanner::set_spacing_rods (SCM smob)
+{
+ Grob *me = unsmob_grob (smob);
+
+ Rod r;
+ Spanner *sp = dynamic_cast<Spanner *> (me);
+ r.item_drul_[LEFT] = sp->get_bound (LEFT);
+ r.item_drul_[RIGHT] = sp->get_bound (RIGHT);
+ r.distance_
+ = robust_scm2double (me->get_property ("minimum-length"), 0);
+
+ r.add_to_cols ();
+ return SCM_UNSPECIFIED;
+}
+
+/*
+ Return I such that SP == SP->ORIGINAL ()->BROKEN_INTOS_[I].
+*/
+int
+broken_spanner_index (Spanner *sp)
+{
+ Spanner *parent = dynamic_cast<Spanner *> (sp->original ());
+ return find (parent->broken_intos_, sp) - parent->broken_intos_.begin ();
+}
+
+Spanner *
+unsmob_spanner (SCM s)
+{
+ return dynamic_cast<Spanner *> (unsmob_grob (s));
+}
+
+ADD_INTERFACE (Spanner,
+ "spanner-interface",
+ "Some objects are horizontally spanned between objects. For\n"
+ "example, slur, beam, tie, etc. These grobs form a subtype called\n"
+ "@code{Spanner}. All spanners have two span-points (these must be\n"
+ "@code{Item} objects), one on the left and one on the right. The left bound is\n"
+ "also the X-reference point of the spanner.\n",
+ "minimum-length");