That it’s neither supported by default, nor mentioned in the documentation. Which leads to people misconfiguring their webservers, e.g., https://caddyserver.com./ vs https://httpd.apache.org./
It is not _configured_ by default. There is an important distinction.
It's not mentioned in documentation because the documentation [1] does not provide an _exhaustive_ list of the kinds of addresses that Caddy can be configured to serve.
1. https://caddyserver.com/docs/caddyfile/concepts#addresses