private function setAlternatives(array $sitemapUrlList, SitemapUrl $sitemapUrl)
    {
        foreach ($sitemapUrlList as $sitemapUrlFromList) {
            // Add current as alternative to exist.
            $sitemapUrlFromList->addAlternateLink(
                new SitemapAlternateLink($sitemapUrl->getLoc(), $sitemapUrl->getLocale())
            );

            // Add others as alternative to current.
            $sitemapUrl->addAlternateLink(
                new SitemapAlternateLink($sitemapUrlFromList->getLoc(), $sitemapUrlFromList->getLocale())
            );
        }

        $sitemapUrlList[] = $sitemapUrl;

        return $sitemapUrlList;
    }