Pragma

[mnot@…]

Pragma's definition is much more detailed about its purpose than necessary, considering that it's deprecated. Should be rewritten to reflect how it's actually used. The relationship to Cache-Control also needs to be clarified.

[mnot@…]

Proposal:

3.4. Pragma

The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request that they will understand (as Cache-Control was not defined until HTTP/1.1). When the Cache-Control header is also present and understood in a request, Pragma is ignored.

In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification deprecates such extensions to improve interoperability.

Pragma = 1#pragma-directive pragma-directive = "no-cache" / extension-pragma extension-pragma = token [ "=" ( token / quoted-string ) ]

When the Cache-Control header is not present in a request, the no-cache request pragma-directive MUST have the same effect on caches as if "Cache-Control: no-cache" were present.

When sending a no-cache request, a client SHOULD include both pragma and cache-control directives unless Cache-Control: no-cache is purposefully omitted to target other Cache-Control response directives at HTTP/1.1 caches. For example:

GET / HTTP/1.1 Host: www.example.com Cache-Control: max-age=30 Pragma: no-cache

will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not understand Cache-Control from serving a cached response.

Note: Because the meaning of "Pragma: no-cache" in responses is not specified, it does not provide a reliable replacement for "Cache-Control: no-cache" in them.

[mnot@…]

From [1284]:

Rewrite Pragma section; addresses #292