send-message-to-window in Miscellaneous

• (send-message-to-window x y message) -> value
     x : exact integer in [-10000, 10000]
     y : exact integer in [-10000, 10000]
     message : value

  Finds the frontmost top-level window at (x, y) in global coordinates. If a window is there, this function calls the window's on-message method, providing message as the method's argument; the result of the function call is the result returned by the method. If no MrEd window is at the given coordinates, or if it is covered by a non-MrEd window at (x, y), #f is returned.