private void CancelGrab()
        {
            IntPtr grabHandle;
            bool   grabConfined;

            Drawing.Rectangle grabArea;
            XplatUI.GrabInfo(out grabHandle, out grabConfined, out grabArea);
            if (grabHandle != IntPtr.Zero)
            {
                XplatUI.SendMessage(grabHandle, Msg.WM_CANCELMODE, IntPtr.Zero, IntPtr.Zero);
            }
        }