Client cache time to live. Number of hours until expiration. Used to manage client and proxy server caching.
See catalog::Expiration for details.
Real number, -2, -1, 0, or greater. Number of hours until expiration since the response image was generated. Set to 0 to always expire the response image immediately, which effectively disables client caching. Set to -1 to mark as
never expire; in this case the server always returns 403 status in response to conditional
GET requests without checking whether the file has actually changed. Set to -2 to use the default provided by
attribute::Expiration is used if the field is not present, if the value is -2, or if the field is empty.