>>-substr(n-+--------------------------+--)----------------><
            +-,--+--------+--+------+--+
                 +-length-+  +-,pad-+

Returns a substring from the buffer content that begins at the n'th character and is of length length, padded with pad if necessary. The n must be a positive integer. If n is greater than receiving_string~length, only pad characters are returned. If you omit length, the remaining buffer content is returned. The default pad character is a blank.