Retrieves a handle to the child window at the top of the Z order
#include <WinAPISysWin.au3>
_WinAPI_GetTopWindow ( $hWnd )
| $hWnd | Handle to the parent window whose child windows are to be examined. If this parameter is 0, the function returns a handle to the window at the top of the Z order. |
| Success: | Handle to the child window at the top of the Z order. If the specified window has no child windows, the return value is 0. |
| Failure: | 0, call _WinAPI_GetLastError() to get extended error information. |
Search GetTopWindow in MSDN Library.