Double-click anywhere in the window (except in the black area) to obtain the X and Y coordinates of the mouse relative to the object which fired the event, in this case the BODY.

Click in the black area to obtain the X and Y coordinates of the mouse relative to the event which fired the event, in this case the DIV positioned absolutely at 200px x 300px.

Notice that the offset coordinates also appear in the status window of the browser (lower left corner).