The “Accept-Encoding” header field can be used by user agents to indicate what response content-codings are acceptable in the response. An “identity” token is used as a synonym for “no encoding” in order to communicate when no encoding is preferred. (RFC 7231: Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content)

Section 5.3.4 of RFC 7231 defines “Accept-Encoding” as a request header field only. This specification expands that definition to allow “Accept-Encoding” as a response header field as well. When present in a response, it indicates what content codings the resource was willing to accept in the associated request. A field value that only contains “identity” implies that no content codings were supported. (RFC 7694: Hypertext Transfer Protocol (HTTP) Client-Initiated Content-Encoding)


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