This header can be used in conjunction with a 503 (Service Unavailable) response
to tell the client how soon it can repeat its request.

This header indicates how soon (in seconds) the browser should ask for an updated page.

This header specifies the date of generation of the document

This header indicates when the document was last changed.

This header stipulates the time at which the content should be considered out-of-date

This header specifies expiration date of cookies included in this response.