http_cache_last_modified — Caching by last modification
([ int $timestamp_or_expires
If the supplied argument is greater than 0, it is handled as timestamp
and will be sent as date of last modification. If it is 0 or omitted,
the current time will be sent as Last-Modified date.
If it's negative, it is handled as expiration time in seconds, which means
that if the requested last modification date is not between the calculated timespan,
the Last-Modified header is updated and the actual body will be sent.
A log entry will be written to the cache log if the INI setting
http.log.cache is set
and the cache attempt was successful.
Note: This function may be used in conjunction with
http_send_data(), http_send_file() and http_send_stream().
Returns FALSE or exits on success with 304 Not Modified if the entity is cached.
See the INI setting
http.force_exit for what "exits" means.
Example #1 A http_cache_last_modified() example