private function blockArg($nodes, $id, $start, $end, $otag, $ctag, $level)
    {
        $key = $this->block($nodes);
        $keystr = var_export($key, true);
        $id = var_export($id, true);

        return sprintf($this->prepare(self::BLOCK_ARG, $level), $id, $key);
    }