Что такое группы HTTP статус-кодов?

1xx — Informational: 100 Continue, 101 Switching Protocols. 2xx — Success: 200 OK, 201 Created, 202 Accepted, 204 No Content. 3xx — Redirection: 301 Moved Permanently, 302 Found, 304 Not Modified. 4xx — Client Error: 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 405 Method Not Allowed, 409 Conflict, 422 Unprocessable Entity, 429 Too Many Requests. 5xx — Server Error: 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout. QA знает наизусть наиболее частые.