+MAKE_SCHEME_CALLBACK (Side_position_interface, move_to_extremal_staff, 1);
+SCM
+Side_position_interface::move_to_extremal_staff (SCM smob)
+{
+ Grob *me = unsmob_grob (smob);
+ System *sys = dynamic_cast<System*> (me->get_system ());
+ Direction dir = get_grob_direction (me);
+ if (dir != DOWN)
+ dir = UP;
+
+ Interval iv = me->extent (sys, X_AXIS);
+ iv.widen (1.0);
+ Grob *top_staff = sys->get_extremal_staff (dir, iv);
+
+ if (!top_staff)
+ return SCM_BOOL_F;
+
+ // Only move this grob if it is a direct child of the system. We
+ // are not interested in moving marks from other staves to the top
+ // staff; we only want to move marks from the system to the top
+ // staff.
+ if (sys != me->get_parent (Y_AXIS))
+ return SCM_BOOL_F;
+
+ me->set_parent (top_staff, Y_AXIS);
+ me->flush_extent_cache (Y_AXIS);
+ Axis_group_interface::add_element (top_staff, me);
+
+ // Remove any cross-staff side-support dependencies
+ Grob_array *ga = unsmob_grob_array (me->get_object ("side-support-elements"));
+ if (ga)
+ {
+ vector<Grob*> const& elts = ga->array ();
+ vector<Grob*> new_elts;
+ for (vsize i = 0; i < elts.size (); ++i)
+ {
+ if (me->common_refpoint (elts[i], Y_AXIS) == top_staff)
+ new_elts.push_back (elts[i]);
+ }
+ ga->set_array (new_elts);
+ }
+ return SCM_BOOL_T;
+}
+
+