def span_tokenize(self, s):
return<EOL>
Identify the tokens using integer offsets `(start_i, end_i)` rather than copying them to a new sequence

        The sequence of tokens (strings) can be generated with

            `s[start_i:end_i] for start_i, end_i in span_tokenize(s)`

        Returns:
          generator of 2-tuples of ints, like ((int, int) for token in s)