UnTextWin() - Replace characters within an area
 Replaces an area of characters from a region of the screen
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 Syntax

     UnTextWin( <nTop>, <nLeft>, <nBottom>, <nRight>,
        <cReplacementChar | nReplacementChar>,
        [<cInitialChar | nInitialChar>],
        [<cEndChar | nEndChar>]) --> cNull

 Arguments

     <nTop> is the top row coordinate of the area.

     <nLeft> is the left column coordinate of the area.

     <nBottom> is the bottom row coordinate of the area.

     <nRight> is the right column coordinate of the area.

     <cReplacementChar | nReplacementChar> is the character that is used to
     replace existing characters with.

     <cInitialChar | nInitialChar> is the lower boundary for characters
     that should not be cleared from the screen. This charcacter can be in
     the range 0 to 255. The default is CHR(176) or ░.

     <cEndChar | nEndChar> is the upper boundary for charcters to be
     excluded from the replacement. This character can be in the range 0 -
     255 with the default being CHR(223) or ▀.


 Returns

     UnTextWin() always returns null string, or "".

 Description

     UnTextWin() may be used to selectively clear parts of the currently
     active window. You can set lower and higher boundaries for charcters to
     be kept on the scrren using the <cInitialChar | nInitialChar> and
     <cEndChar | nEndChar> parameters.

     Any characters falling outisde of these characters ranges will be
     replaced with <cReplacementChar | nReplacementChar>.

 Notes

     ■  This function does not alter the cursor position.

     ■  If you declare a lower bundary of 225 and a higher boundary of 20,
        then all characters between 225-255 and 0-20 will be kept.


 Examples

     ■  Clear the screen, with the exception of the boxes.  Since no
        range is specified, 176 to 223 are bracketed out:

        UnTextWin(0, 0, MaxRow(), MaxCol(), " ")

     ■  Clear all characters within the currently active window, with the
        exception of uppercase letters (65-90).  A numeric BLANK may be used as
        a clear character:

        UnTextWin(0, 0, MaxRow(), MaxCol(), 32, 65, 90)

     ■  Double back on an area.  All characters with the exception of
        uppercase letters are deleted from the currently active window:

        UnTextWin(0, 0, MaxRow(), MaxCol(), 255, 91, 64)


 Files:  Library is MRWINDOW.LIB.