+
+/* Half of the height, in staff space, i.e. 2.0 for a normal staff. */
+Real
+Staff_symbol_referencer::staff_radius (Grob *me)
+{
+ return (line_count (me) - 1) / 2.0;
+}
+
+int
+compare_position (Grob *const &a, Grob *const &b)
+{
+ return sign (Staff_symbol_referencer::get_position ((Grob*)a)
+ - Staff_symbol_referencer::get_position ((Grob*) b));
+}
+
+ADD_INTERFACE (Staff_symbol_referencer,"staff-symbol-referencer-interface",
+ "An object whose Y position is meant relative to a staff "
+ "symbol. "
+ "These usually have @code{Staff_symbol_referencer::callback} "
+ "in their @code{Y-offset-callbacks}. "
+ ,
+ "staff-position");
+