+void LinearArrangement::expand()
+{
+ if(gravity==primary)
+ throw arrangement_error("already split");
+ if(edges[primary].empty())
+ throw arrangement_error("no widgets");
+
+ add_constraint(*edges[primary].widgets.front(), get_align_constraint(primary), primary);
+ layout.set_expand(*edges[primary].widgets.front(), false, true);
+ edges[primary].align();
+ gravity = primary;
+}
+