Editing Web server (section)

==== Error message ====
A web server program may reply to a client request message with many kinds of error messages, anyway these errors are divided mainly in two categories:
* [[HTTP client errors]], due to the type of request message or to the availability of requested web resource;<ref name="rfc7231-6.5">{{cite IETF |rfc=7231 |sectionname=Client Error 4xx|section=6.5|title=RFC 7231, HTTP/1.1: Semantics and Content|page=58}}</ref>
* [[HTTP server errors]], due to internal server errors.<ref name="rfc7231-6.6">{{cite IETF |rfc=7231 |sectionname=Server Error 5xx|section=6.6|title=RFC 7231, HTTP/1.1: Semantics and Content|pages=62-63}}</ref>

When an error response / message is received by a client browser, then if it is related to the main user request (e.g. an URL of a web resource such as a web page) then usually that error message is shown in some browser window / message.