def on_mouse_scroll(self, x, y, scroll_x, scroll_y):
children_under_mouse = self.__find_children_under_mouse(x, y)<EOL>if self.propagate_mouse_events:<EOL><INDENT>for child in children_under_mouse.current:<EOL><INDENT>child.dispatch_event('<STR_LIT>', x, y, scroll_x, scroll_y)<EOL><DEDENT><DEDENT>
React to the mouse scroll wheel being turned.

The ``on_mouse_scroll`` event is propagated to any children under the 
mouse.