How to handle new username subreddits?

I can't find an example anymore, but there are new subreddits that link directly to a username.

  1. can someone share an example of such a subreddit/username?
  2. what is the regex for these?

From the old subreddit code, I was able to extract some subreddit regular expressions:

regex = re.compile(r"^([A-Za-z0-9_]{3,21})$")
    prefixed_regex = re.compile(r"^(?:\/?r\/)([A-Za-z0-9_]{3,21})$")
    flex_regex = re.compile(r"^(?:\/?r\/)?([A-Za-z0-9_]{3,21})$")

How can I change my regex to capture the new subreddit/usernames?