In the Windows API there is a message DM_REPOSITION that can be sent to dialogs. When the dialog manager recieves this message it will reposition the dialog so that the entire dialog is visisble on the screen. If the entire dialog is already visible on the screen then no action is taken.
This is a useful thing to be able to do. It allows the programmer to move or resize a dialog and be sure that it is still on the screen for the user. It is also useful for systems with multiple monitors.