They have to handle it anyway. There's nothing in the HTTP specifications that disallows a server from using whatever codes it wants to that aren't specifically

They have to handle it anyway. There's nothing in the HTTP specifications that disallows a server from using whatever codes it wants to that aren't specifically specified. There is no "HTTP 527 Server Needs a Nap" but it is perfectly legal for my server to reply to clients with that HTTP status, and clients are expected to handle it like they would handle any other non-specific error in the 5xx class of response codes (server error). Other perfectly legal responses: 242 - TOO MUCH COFFEE (Server is overcaffeinated and processing requests too quickly) 299 - SUCCESSFUL BUT SASSY (Request succeeded but the server is throwing shade about it) 333 - QUANTUM UNCERTAINTY (The server simultaneously succeeded and failed until observed) 452 - EXCESSIVE TOAST