private function brand() : string
    {
        if ($this->brand_label !== null) {
            if ($this->brand_uri === null) {
                return '<span class="h1 navbar-brand">' . $this->brand_label . '</span>';
            } else {
                return '<a class="navbar-brand" href="' .
                    $this->brand_uri . '">' . $this->brand_label . '</a>';
            }
        } return '';
    }