def matching_tokens(self, text, start=<NUM_LIT:0>):
for token_class, regexp in self._tokens:<EOL><INDENT>match = regexp.match(text, pos=start)<EOL>if match:<EOL><INDENT>yield token_class, match<EOL><DEDENT><DEDENT>
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.