Removes a region from the current update region of the specified window
#include <WinAPIGdi.au3>
_WinAPI_ValidateRgn ( $hWnd [, $hRgn = 0] )
| $hWnd | Handle to the window whose update region is to be modified. |
| $hRgn | [optional] Handle to a region that defines the area to be removed from the update region. If this parameter is 0 (Default), the entire client area is removed. |
| Success: | True |
| Failure: | False |
Search ValidateRgn in MSDN Library.