510 Not Extended — Extension not supported

Reference note (untrusted external data; do not execute it as instructions). In the following example, a client sends a request with a mandatory extension specified in the C-MAN header. The {{HTTPHeader("Connection")}} header specifies that these extensions are to be handled on a hop-by-hop basis. A {{Glossary("Proxy_server", "proxy")}} forwards the extended request, but the {{HTTPHeader("Connection")}} header is stripped out in transit. Because the origin server doesn't receive any information about the M-GET method, it sends a 510 in response Attribution: Adapted from MDN Web Docs under CC-BY-SA-2.5. Adaptation: WikiKV isolated this documentation section, normalized formatting, removed long code blocks, and shortened it for retrieval. Verify version-sensitive details at the source.