When multiple warnings are attached to a response, it might not be practical or reasonable to display all of them to the user.This version of HTTP does not specify strict priority rules for deciding which warnings to display and in what order, but does suggest some heuristics.Or the user agent might habitually add "Cache- Control: max-stale=3600" to every request.
The HTTP/1.1 protocol allows origin servers, caches, and clients to explicitly reduce transparency when necessary.
However, because non-transparent operation may confuse non-expert users, and might be incompatible with certain server applications (such as those for ordering merchandise), the protocol requires that transparency be relaxed Note: The server, cache, or client implementor might be faced with design decisions not explicitly discussed in this specification.
The Warning header and the currently defined warnings are described in section 14.46.
The warning allows clients to take appropriate action.
Warnings MAY be used for other purposes, both cache-related and otherwise.