Sets the mouse capture to the specified window belonging to the current thread
#include <WinAPISys.au3>
_WinAPI_SetCapture ( $hWnd )
| $hWnd | Handle to the window in the current thread that is to capture the mouse |
| Success: | handle to the window that had previously captured the mouse |
| Failure: | 0 |
Search SetCapture in MSDN Library.