Alternative solution?

How is it possible that this is a valid solution, if in the curriculum doesn’t talk about ()

let username = "JackOfAllTrades";
let userCheck = /^[a-z]([0-9][0-9]+|[a-z]+\d*)$/i; // Change this line
let result = userCheck.test(username);
console.log(result, username.match(userCheck))

Challenge: Restrict Possible Usernames

Link to the challenge:
https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/restrict-possible-usernames

@FMGordillo It is just an example of one possible solution. There are other solutions shown based on things you have already learned in the curriculum. The other solutions just show you ways to do it in the hopes you will search out or ask about how they work.