src/Hostname.php
private static function myNormalizeTld(?string &$tld = null): void
    {
        if ($tld !== null) {
            $tld = strtolower($tld);
        }
    }
private static function myNormalizeTld(?string &$tld = null): void
    {
        if ($tld !== null) {
            $tld = strtolower($tld);
        }
    }
private static function myNormalizeTld ( ? string & $ tld = null ) : void { if ( $ tld !== null ) { $ tld = strtolower ( $ tld ) ; } }
Normalizes a top-level domain.

@param string|null $tld The top-level domain.
Normalizes a top - level domain .