The purpose of the Cache-Control header is to specify to clients and any intermediate caches the conditions and restrictions for caching of content.

The syntax of the Cache-Control header is defined as follows.

 CCdir   = "max-age" / "must-revalidate" / 
           "no-store" / "private" / "proxy-revalidate" /
           "public" / " proxy-public" / "user-public" /
           x-wms-event-subscription / "x-wms-proxy-split" /
           "x-wms-content-size" / "x-wms-stream-type"
 Cache-Control = "Cache-Control: " "no-cache" *12("," [SP] CCdir) CRLF

The optional directives defined by the CCdir ABNF syntax element are defined only for use in responses to requests.<2>


 Cache-Control: no-cache, x-wms-content-size=638066, 

The subsequent directives (max-age through x-wms-stream-type) are defined for the Cache-Control header when used in the response to a request.