Expires — specifies date when the resource becomes stale. It relies on servers and clients having accurate clocks and supporting time zones correctly.
Cache-control: max-age takes precedence over
Expires, and is generally more reliable.
pre-check directives are non-standard Internet Explorer extensions that enable use of stale responses. The standard alternative is
Pragma: no-cache — obsoleted in 1999.
Cache-control should be used instead.