This is called when a window is moved on the screen to another location.
The handler is registered by defining it with an HTML tag attribute.
The event is also triggered when a window is moved under control of a script with the moveTo() or moveBy() methods.
This is not supported by Netscape Navigator 4 on the Unix platform.
On the Macintosh platform, Netscape Navigator calls the onmove handler twice when the window is moved.