twMConfine( nTop, nLeft, nBottom, nRight, lAbs )
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     Confine the mouse cursor to a specified region in either absolute
     screen coordinates or window coordinates for the current window.

       Arguments:

     nTop,nLeft,nBottom,nRight - 'N' Coordinates of the region in which
                                     to confine the mouse cursor.

     lAbs - 'L' Logical to indicate whether screen or window
                coordinates are to be used. If TRUE, this function uses
                screen coordinates.

       Return:

     NIL

       Example:

     twMConfine( 3, 3, 10, 10, .T. )

     Confines the mouse cursor to a region bounded by 3, 3, 10, 10 in
     the current window.