- Header Field Definitions
5.1. Age
5.2. Cache-Control
5.2.1. Request Cache-Control Directives
5.2.2. Response Cache-Control Directives
5.2.3. Cache Control Extensions
5.3. Expires
5.4. Pragma
5.5. Warning
5.5.1. Warning: 110 - "Response is Stale"
5.5.2. Warning: 111 - "Revalidation Failed"
5.5.3. Warning: 112 - "Disconnected Operation"
5.5.4. Warning: 113 - "Heuristic Expiration"
5.5.5. Warning: 199 - "Miscellaneous Warning"
5.5.6. Warning: 214 - "Transformation Applied"
5.5.7. Warning: 299 - "Miscellaneous Persistent Warning" ..32