CharWin() - Replaces screen characters
 Replaces specific characters
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 Syntax

     CharWin( [<nTop>,<nLeft>,<nBottom>, <nRight>, [<cNewChar | nNewChar>],
        [<cOldChar | nOldChar>]]) --> cNull

 Arguments

     <nTop>  top coordinate for the top-left corner of the window area.

     <nLeft>  left coordinate for the top-left corner of the window area.

     <nBottom>  bottom coordinate for the bottom-right corner of the
     window area.

     <nRight>  right coordinate for the bottom-right corner of the window
     area.

     <cNewChar | nNewChar>  is the new character for the screen area.
     Specify the parameter as a numeric in the range of 0 to 255 or as a
     character string.  The default value is the character 255.

     <cOldChar | nOldChar>  is the character to exchange.  Specify the
     parameter as a numeric in the range of  0 to 255 or as a character
     string.  The default is to exchange all characters.

     ()  When no parameter is designated, the function replaces all
     characters in the screen area with character 255.

 Returns

     The function always returns a null string for compatibility with
     CA-Tools.

 Description

     If the current output area is a window then this function will apply to
     a window and not the application window. If there are no windows open,
     then the following applies to the application window.

     Within a window or the application window, CharWin() replaces instances
     of a character, or all characters with a new one.  If <cNewchar |
     nNewchar> is not passed a parameter then a CHR(255) is used by default.
     The top-left and bottom-right corner rows and columns are given for the
     borders of the area.  If these arguments are missing, then the entire
     area of the current window is used - if a window is opened and selected,
     otherwise the application window is used.

     If [<cNewChar | nNewChar>] is not specified then the CLEARB character is
     used.

 Notes

     ■  If a window is currently selected, the this function will be applied
        to the window.

     ■  This function does not alter the cursor position.

 Examples

     ■  Replace all "B" for "A" in the current window

        CharWin( 0, 0, MaxRow(), MaxCol(), "B", "A")


     ■  Numeric characters can also be designated:

        CharWin( 0, 0, MaxRow(), MaxCol(), 66, 65)

 Files:  Library is MRWINDOW.LIB.