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 UNTEXTWIN()
 Replaces an area of characters from a region of the screen
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 Syntax

     UNTEXTWIN(<nTopLine>, <nLeftColumn>, <nBottomLine>,
        <nRightColumn>,
        <cReplacementCharacter|nReplacementCharacter>,
        [<cInitialCharacter|nInitialCharacter>],
        [<cEndCharacter|nEndCharacter>]) --> cNull

 Arguments

     <nTopLine>  Designates the line for the upper-left corner of the
     area.

     <nLeftColumn>  Designates the column for the upper-left corner of
     the area.

     <nBottomLine>  Designates the line for the bottom-right corner of
     the area.

     <nRightColumn>  Designates the line for the bottom-right column of
     the area.

     <cReplacementCharacter|nReplacementCharacter>  Replaces each
     character within the window, with the exception of those within the
     range of <cInitialCharacter|nInitialCharacter> and
     <cEndCharacter|nEndCharacter>.

     <cInitialCharacter|nInitialCharacter>  Designates the beginning of
     the bracketed area.  The character can be number in the range of 0 to
     255, or the character string type.  The default value is 176.

     <cEndCharacter|nEndCharacter>  Designates the end of the bracketed
     area.  The character can be number in the range of 0 to 255 or the
     character string type.  The default value is 223.

 Returns

     UNTEXTWIN() always returns a null string.

 Description

     Use UNTEXTWIN() to delete particular character from within a screen
     area.  You can bracket off a specific area of characters.  This area
     begins with <cInitialCharacter|nInitialCharacter> and ends with
     <cEndCharacter|nEndCharacter>.  The preset values have bracketed out
     characters 176 to 223 (the graphics characters).  This allows you to
     clear a screen, but retain the boxes.

     The designated area can even "double back"; EndCharacter could be
     smaller than Initial Character.  In this case, the area stretches from
     the larger value to 255 and, inclusive of 0, to the smaller value.  You
     might say these two areas are designated.

 Examples

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

        UNTEXTWIN(0, 0, 24, 79, " ")               // ""

     .  Clear all characters, with the exception of uppercase letters
        (65-90).  A numeric BLANK is designated as a clear character:

        UNTEXTWIN(0, 0, 24, 79, 32, 65, 90)        // ""

     .  Double back on an area.  All characters with the exception of
        uppercase letters are deleted:

        UNTEXTWIN(0, 0, 24, 79, 255, 91, 64)       // ""