What does the HTTP status codes 1XX represents?

The 1xx (Informational) class of HTTP status codes indicates a provisional response, consisting only of the Status-Line and optional headers, and is terminated by an empty line. These codes indicate that the request was received and the process is continuing. A client MUST be prepared to accept one or more 1xx responses before a regular response, even if the client does not expect a 100 (Continue) status message. For example, 100 Continue indicates that the initial part of a request has been received and has not yet been rejected by the server.

B. Client error responses are represented by the 4xx status code class (e.g., 404 Not Found).
C. Success responses are represented by the 2xx status code class (e.g., 200 OK).
D. Redirection messages are represented by the 3xx status code class (e.g., 301 Moved Permanently).

1. Fielding, R., et al. (2022). RFC 9110: HTTP Semantics. Internet Engineering Task Force (IETF). Section 15.2, "Informational 1xx".

2. MDN Web Docs. (2023). HTTP response status codes. Mozilla. Section: "Informational responses". (Note: While MDN is vendor documentation, it is a highly reputable and standard reference for web technologies, directly reflecting IETF standards).