$urlSet = new Thepixeldeveloper\Sitemap\Urlset(); 

$url = (new Thepixeldeveloper\Sitemap\Url($loc))
  ->setLastMod($lastMod)
  ->setChangeFreq($changeFreq)
  ->setPriority($priority);

$urlSet->addUrl($url);

$sitemapIndex = new Thepixeldeveloper\Sitemap\SitemapIndex(); 

$url = (new Thepixeldeveloper\Sitemap\Sitemap($loc))
  ->setLastMod($lastMod);
  
$sitemapIndex->addSitemap($url);

echo (new Thepixeldeveloper\Sitemap\Output())->getOutput($sitemapIndex);

$subelement = new Thepixeldeveloper\Sitemap\Subelements\Image('https://s3.amazonaws.com/path/to/image');

$subelement = new Thepixeldeveloper\Sitemap\Subelements\Video('thumbnail', 'title', 'description');

$subelement = new Thepixeldeveloper\Sitemap\Subelements\Mobile();

$subelement = new Thepixeldeveloper\Sitemap\Subelements\Link('de', 'http://www.example.com/schweiz-deutsch/');

$subelement = (new Thepixeldeveloper\Sitemap\Subelements\News())
    ->setPublicationDate(new \DateTime())
    ->setPublicationLanguage('en')
    ->setPublicationName('Site Name')
    ->setTitle('Some title');

$url = new Thepixeldeveloper\Sitemap\Url('http://www.example.com/1')
$url->addSubelement($subelement);

echo (new Thepixeldeveloper\Sitemap\Output())
    ->setIndented(false)
    ->getOutput($urlSet);