5. The Priority HTTP Header Field

The Priority HTTP header field is a Dictionary that carries priority parameters (see Section 4). It can appear in requests and responses. It is an end-to-end signal that indicates an endpoint's view of how the HTTP response should be prioritized. Section 8 describes how intermediaries combine priority information sent from clients and servers. Clients cannot interpret the presence or absence of a Priority response header field as acknowledgement that any prioritization has occurred. Sections 9 and 10 provide guidance on how endpoints act on Priority header values.

HTTP requests with a Priority header field might be cached and reused for subsequent requests; see [CACHING]. When an origin server generates a Priority response header field based on properties of the HTTP request it receives, the server ought to control the cacheability or applicability of the cached response by using header fields that control the caching behavior, such as Cache-Control and Vary.

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