public function getTokenParser($tag)
    {
        if (isset($this->parsers[$tag])) {
            return $this->parsers[$tag];
        }
        $broker = end($this->brokers);
        while (false !== $broker) {
            $parser = $broker->getTokenParser($tag);
            if (null !== $parser) {
                return $parser;
            }
            $broker = prev($this->brokers);
        }
    }