Category "http-response-codes"

Non integer HTTP response codes possible?

I am aware of standard HTTP response codes and their categorization (1xx, 2xx, 3xx, 4xx and 5xx) But, I have seen certain web requests return non-standard HTTP

403 Forbidden vs 401 Unauthorized HTTP responses

For a web page that exists, but for which a user does not have sufficient privileges (they are not logged in or do not belong to the proper user group), what is