The client may then decide to cache the representation, along with its ETag. Later, if the client wants to retrieve the same URL resource again, it will first determine whether the locally cached version of the URL has expired (through the Cache-Control and the Expire headers). If the URL has not expired, it will retrieve the locally cached resource. If it is determined that the URL has expired (is "stale"), the client will send a request to the server that includes its previously-saved copy of the ETag in the "If-None-Match" field.