INVERTWIN()
 Inverts all attributes in an area of the screen
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 Syntax

     INVERTWIN([<nTopLine>], [<nLeftColumn>],
        [<nBottomLine>], [<nRightColumn>]) --> cNull

 Arguments

     <nTopLine>  Designates the topmost line for the top-left corner of
     the area.  The default is the cursor position.

     <nLeftColumn>  Designates the leftmost column for the top-left
     corner of the area.  The default is the cursor position.

     <nBottomLine>  Designates the bottommost line for the bottom-right
     corner of the area.  The default is the end of the screen area.

     <nRightColumn>  Designates the rightmost column for the bottom-right
     corner of the area.  The default is the end of the screen area.

 Returns

     The function always returns a null string.

 Description

     This function permits you to invert all attributes within a screen area.
     Background attributes are exchanged for those in the foreground.

 Examples

     .  Invert the attributes in an area:

        INVERTWIN(10, 10, 20, 70)      // Always returns a null string

     .  Invert to end of screen:

        INVERTWIN(10, 10)