+/* This is like generic_group_extent, but it only counts the grobs that
+ are children of some other axis-group. This is uncached; if it becomes
+ commonly used, it may be necessary to cache it somehow. */
+Interval
+Axis_group_interface::staff_extent (Grob *me, Grob *refp, Axis ext_a, Grob *staff, Axis parent_a)
+{
+ extract_grob_set (me, "elements", elts);
+ vector<Grob*> new_elts;
+
+ for (vsize i = 0; i < elts.size (); i++)
+ if (elts[i]->common_refpoint (staff, parent_a) == staff)
+ new_elts.push_back (elts[i]);
+
+ return relative_group_extent (new_elts, refp, ext_a);
+}
+