public function at($name, $entity, $options=null)
    {
        $index = $this->__find__($name);
        if( is_object($options) ) $opt = $options;
        else $opt = is_array($options) ? (object)$options : new \stdClass();

        if ($index === -1) { throw new \Exception('Parser rule not found: ' . $name); }

        $this->__rules__[$index]->setEntity($entity);
        $this->__rules__[$index]->alt = isset($opt->alt) ? $opt->alt : [];
        $this->__cache__ = null;
    }