RFC 7234 Hypertext Transfer Protocol (HTTP/1.1): Caching

PROPOSED STANDARD · June 2014 · R. Fielding, Ed., M. Nottingham, Ed., J. Reschke, Ed.

The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.

Not ingested in full here — read it on rfc-editor.org.