protected function getStructureXml()
    {
        $struct = '<?xml version="1.0" encoding="UTF-8"?>';
        $struct .= '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" NAMESPACES>URLS</urlset>';

        $namespaces = '';
        foreach ($this->customNamespaces as $key => $location) {
            $namespaces .= ' xmlns:' . $key . '="' . $location . '"';
        }

        $struct = str_replace('NAMESPACES', $namespaces, $struct);

        return $struct;
    }