Regular Expressions - Restrict Possible Usernames: Question about the Solutions

So I was super-stumped on this one, and checked the given solutions, but I was very confused about the curly braces used in the example solutions. Maybe I missed something, but when did we go over using the curly braces to limit the amount of characters that are tested in a code? That’s a very important lesson that I wish we had a chance to learn about!

Challenge: Regular Expressions - Restrict Possible Usernames

Link to the challenge:

Thank you for the speedy reply!

I got to that lesson not to long ago. I guess I was just wondering why they would introduce it in a solution when they hadn’t covered it yet :sweat_smile:

The solutions are just ways to solve the challenge and are not restricted to only what has been taught in previous lessons/challenges. Some users may already have learned about that regex syntax and are able to incorporate it into a solution. People come to the curriculum for all backgrounds and could have been exposed to regular expression somewhere else. Also, some users will do their own research while working through a challenge and may discover other syntax to solve a challenge that may or may not be introduced in a later challenge.