“在请求头Expect中指定的预期内容无法被服务器满足，或者这个服务器是一个代理服务器，它有明显的证据证明在当前路由的下一个节点上，Expect的内 容无法被满足。“ — wikipedia

“The expectation given in an Expect request-header field could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.“ — ietf