Expect |
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The Expect header is used by clients to let servers know that they expect certain behavior. This header currently is closely tied to the response code 100 Continue (see Section 3.4.1).
If a server does not understand the Expect header's value, it should respond with a status code of 417 Expectation Failed.
Request header
Expect: 1# ("100-continue" | expectation-extension)
Expect: 100-continue