protected function fillSitemapIndex( $sitemap, $numberOfResults, $root )
    {
        $numberOfPage = (int)ceil( $numberOfResults / static::PACKET_MAX );
        for ( $sitemapNumber = 1; $sitemapNumber <= $numberOfPage; $sitemapNumber++ )
        {
            $sitemapElt       = $sitemap->createElement( "sitemap" );
            $locUrl           = $this->generateUrl( "_novaseo_sitemap_page", [ "page" => $sitemapNumber ], UrlGeneratorInterface::ABSOLUTE_URL );
            $loc              = $sitemap->createElement( "loc", $locUrl );
            $date             = new DateTime();
            $modificationDate = $date->format( 'c' );
            $mod              = $sitemap->createElement( 'lastmod', $modificationDate );
            $sitemapElt->appendChild( $loc );
            $sitemapElt->appendChild( $mod );
            $root->appendChild( $sitemapElt );
        }
    }