def span_tokenize_sents(self, strings):
for s in strings:<EOL><INDENT>yield list(self.span_tokenize(s))<EOL><DEDENT>
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)))