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  REVATTR()                                                   Video Function
 Purpose..: Reverse the attribute for a rectangle on screen
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 Syntax...: RevAttr( [<nTRow>[, <nLCol>[, <nBRow>[,
                      <nRCol>]]]], [<nColor>] ) --> NIL

 Arguments: [<nTRow>]   = Top row.
            [<nLCol>]   = Left column.
            [<nBRow>]   = Bottom row.
            [<nRCol>]   = Right column.
            [<nColor>]  = Integer representing color attribute.
                          The formula is ...nFore + ( nBack * 16 ).

 Returns..: NIL

 Remark...: It is a high speed function to reverse the color of a
            specified rectangle of screen without disturbing any text on
            the screen. If the specified screen rectangle has a white
            Fore and blue Back, the function will change to blue in the
            Fore and white in the background. The function is capable of
            reversing all color attributes in a rectangle containing
            multiple color combinations. If <nColor> is passed, it will
            be reversed. The default is the full screen.

 Source...: REVATTR.C
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 Example..: The example will change all the screens colors
            to their reverse attributes without changing
            or overwriting any text that maybe on the screen.
            Like all of these functions, it uses direct video
            writes for speed.

              RevAttr( 0, 0, MaxRow(), MaxCol() )