Retrieve all token definitions matching the beginning of a text.

        Args:
            text (str): the text to test
            start (int): the position where matches should be searched in the
                string (see re.match(rx, txt, pos))

        Yields:
            (token_class, re.Match): all token class whose regexp matches the
                text, and the related re.Match object.

def matching_tokens(self, text, start=0):
        """Retrieve all token definitions matching the beginning of a text.

        Args:
            text (str): the text to test
            start (int): the position where matches should be searched in the
                string (see re.match(rx, txt, pos))

        Yields:
            (token_class, re.Match): all token class whose regexp matches the
                text, and the related re.Match object.
        """
        for token_class, regexp in self._tokens:
            match = regexp.match(text, pos=start)
            if match:
                yield token_class, match