* 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
* 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