/**
  * Cookie domain, for example 'www.php.net'.
  * 
  * To make cookies visible on all subdomains then the domain
  * must be prefixed with a dot like '.php.net'.
  * 
  * @param string $domain The domain to set
  */
 public static function set_cookie_domain($domain)
 {
     self::$cookie_domain = $domain;
 }