+Grob *
+System::get_vertical_alignment ()
+{
+ extract_grob_set (this, "elements", elts);
+ Grob *ret = 0;
+ for (vsize i = 0; i < elts.size (); i++)
+ if (Align_interface::has_interface (elts[i]))
+ {
+ if (ret)
+ programming_error ("found multiple vertical alignments in this system");
+ ret = elts[i];
+ }
+
+ if (!ret)
+ programming_error ("didn't find a vertical alignment in this system");
+ return ret;
+}
+
+// Finds the furthest staff in the given direction whose x-extent
+// overlaps with the given interval.
+Grob *
+System::get_extremal_staff (Direction dir, Interval const &iv)
+{
+ Grob *align = get_vertical_alignment ();
+ if (!align)
+ return 0;
+
+ extract_grob_set (align, "elements", elts);
+ vsize start = (dir == UP) ? 0 : elts.size () - 1;
+ vsize end = (dir == UP) ? elts.size () : VPOS;
+ for (vsize i = start; i != end; i += dir)
+ {
+ if (Hara_kiri_group_spanner::has_interface (elts[i]))
+ Hara_kiri_group_spanner::consider_suicide (elts[i]);
+
+ Interval intersection = elts[i]->extent (this, X_AXIS);
+ intersection.intersect (iv);
+ if (elts[i]->is_live () && !intersection.is_empty ())
+ return elts[i];
+ }
+ return 0;
+}
+