If I set: ErrorDocument 404 "404 Not found" The message will be sent with header: Content-Type: text/html; charset=iso-8859-1 Instead, it should use text/plain. People are very unlikely to put a valid HTML document between the quotes in the directive.
On a related note: I tried ErrorDocument 404 "" which I think is allowed per the documentation https://httpd.apache.org/docs/2.4/custom-error.html However I get the following: AH00526: Syntax error on line ... ErrorDocument takes two arguments, Change responses for HTTP errors ErrorDocument 404 " " does not give an error, but it not exactly what I wanted.
Related to https://bz.apache.org/bugzilla/show_bug.cgi?id=65699