code: def span_tokenize_sents(self, strings):
          
          raise NotImplementedError("span_tokenizer and span_tokenzie_sents not yet implemented. ;)")
          for s in strings:
              yield list(self.span_tokenize(s))
docs: Apply ``self.span_tokenize()`` to each element of ``strings``.  I.e.:
              return iter((self.span_tokenize(s) for s in strings))
          :rtype: iter(list(tuple(int, int)))