`generator` : the tokens in this segment

def tokens(self):
        """
        `generator` : the tokens in this segment
        """
        for subsegment_or_token in self:
            if isinstance(subsegment_or_token, Segment):
                subsegment = subsegment_or_token
                for token in subsegment.tokens():
                    yield token
            else:
                token = subsegment_or_token
                yield token