/**
  * Returns true if the response must be revalidated by caches.
  *
  * This method indicates that the response must not be served stale by a
  * cache in any circumstance without first revalidating with the origin.
  * When present, the TTL of the response should not be overridden to be
  * greater than the value provided by the origin.
  *
  * @return bool true if the response must be revalidated by a cache, false otherwise
  *
  * @api
  */
 public function mustRevalidate()
 {
     return parent::mustRevalidate();
 }