_twM2()
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    Hide the mouse cursor and decrement the internal cursor flag by 1.
    The internal flag has a maximum value of zero and all calls to
    _twM2() decrease it by one. The mouse cursor will show only when
    the internal flag is zero. Therefore if you make successive calls to
    _twM2(), in order to display the mouse cursor, you must make a
    corresponding number of calls to _twM1() to display it again.
    _twM2() IS NOT a toggle for _twM1().

       Arguments:

    None.

       Return:

    Nothing.

       Example:

    _twM2()