I’m not sure if this is the correct place to raise this but:

The solution given to this lesson: https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/restrict-possible-usernames

uses the pattern syntax [0-9]{2,0}.

However, that syntax is not taught until 3 lessons later, here:

https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/specify-upper-and-lower-number-of-matches

A different solution (say: /^[a-z][a-z]$|^[a-z][a-z]+[0-9]*$|^[a-z][0-9][0-9]+$/) would work without using the as-of-yet untaught syntax).

Suggest either reordering the lessons, or changing the hinted solution.