8. Merging Client- and Server-Driven Priority Parameters

Intermediaries can receive priority signals from both clients and servers and might need to combine them to determine the priority of forwarded responses.

Priority parameters obtained from a request and those obtained from a response are merged using the following rules:

• If a parameter is present in the response, use the response value.
• Otherwise, if the parameter is present in the request, use the request value.
• Otherwise, use the default value for that parameter.

This rule allows servers to override client-provided priority by including priority parameters in responses. For example, an origin server might know that a resource is critical to page rendering, even if the client requests it with lower urgency.

When a priority parameter is omitted from a request, intermediaries ought to use the default value. When a priority parameter is omitted from a response, intermediaries ought to continue using the value provided in the request (or its default).

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