NAME
       XorRectRegion -- Perform 2d XOR operation of rectangle
                       with region, leaving result in region

   SYNOPSIS
       status = XorRectRegion(region,rectangle)
         d0                     a0      a1

        bool xorrectregion( struct region *, struct rectangle * );

   FUNCTION
        Add portions of rectangle to region if they are not in
        the region.
        remove portions of rectangle from region if they are
        in the region.

   INPUTS
       region - pointer to region structure
       rectangle - pointer to rectangle structure

   RESULTS
        status - return TRUE if successful operation
                 return FALSE if ran out of memory

   BUGS

   SEE ALSO
        orregionregion() andregionregion() graphics/regions.h