public function isSlugEditable()
    {
        if ($this->isSlugEditable === null) {
            $metadata = $this->metadata();

            if (isset($metadata['routable']['editable'])) {
                $this->isSlugEditable = !!$metadata['routable']['editable'];
            } else {
                $this->isSlugEditable = false;
            }
        }

        return $this->isSlugEditable;
    }