Edit: This has been reported on Github already and the issue closed beacuse they are working on new project based curriculum. If you find this thread while searching for a solution, my recommendation is skip this challenge. Do the rest of the curriculum in the section and then do this challenge last. At that point you will have all of the knowledge needed (plus some extra) to solve the challenge.
This Regular Expression challenge requires knowledge of grouping and if you want a more concise solution quantity specifiers in order to solve. Both of these topics are not introduced until later in the Regular Expression curriculum.
This would be a better challenge to do after those topics are introduced and discussed so newcomers to regular expressions won’t struggle as much or just cut and paste one of the solutions found in the guide from Get a hint.
Challenge: Restrict Possible Usernames
Link to the challenge:
Link to Solution Guide:
Link to Github Issue: