private function createCategory()
    {
        $pattern = $this->config["category"];

        $index = [];
        $matches = [];
        foreach ($this->meta as $key => $entry) {
            if (preg_match($pattern, $key, $matches)) {
                $catKey = $matches[1];
                $index[$catKey] = $key;
                $this->meta[$key]["key"] = $catKey;
                $this->meta[$key]["url"] = $key;
                unset($this->meta[$key]["__toc__"]);
            }
        }

        return $index;
    }