@matrix Actually reading the specification it seems like fedi usernames can be any character that is valid as part of an URI. This means (0-9), (A-Z, a-z) and also “~”, “-“, ““, and “.” are valid characters! However, I did some digging around and it seems like Pleroma only supports “-“ and “” of the special character set, it won’t let you make a user containing a period or tilde.

@matrix Actually email supports more characters including !#$%&'*+-/=?^_{|}~`, we can’t do this with ActivityPub because a lot of these characters are special characters in an URI. (however in practise most mail providers don’t allow you sign up with most of these characters while they technically should be allowed by the spec)