An application sends a WM_UNDO message to an edit control to undo the last operation. When this message is sent to an edit control, the previously deleted text is restored or the previously added text is deleted.
WM_UNDO wParam = 0; // not used; must be zero lParam = 0; // not used; must be zero
This message has no parameters.
If the message succeeds, the return value is TRUE; otherwise, it is FALSE.