# File gtk/sample/gtk-demo/changedisplay.rb, line 310
    def find_toplevel_at_pointer(display)
      pointer_window, x, y = display.window_at_pointer

      # The user data field of a GdkWindow is used to store a pointer
      # to the widget that created it.
      if pointer_window
        widget = pointer_window.user_data
      end

      return (if widget
                widget.toplevel
              else
                nil
              end)
    end