I want PHP to retrieve the domain when the current URL is a subdomain.

$pslManager=new Pdp\PublicSuffixListManager();
$parser = new Pdp\Parser($pslManager->getList());

$url='www.domainname.net';
$subdomain=$parser->getSubdomain($url);
$domainName=$parser->getRegisterableDomain($url);

/** $subdomain='www'*/
/** $domainName='domainname.net'*/