If you mistype the username when logging in to include a comma, it gives an error of "The email address is badly formatted." which is not super clear. It probably should read something along the lines of "Usernames can only contain letters, number, periods, and hyphens"
If you mistype the username when logging in to include a comma, it gives an error of "The email address is badly formatted." which is not super clear. It probably should read something along the lines of "Usernames can only contain letters, number, periods, and hyphens"