68 challenges across eight tiers. Tier 8 is a warm-up; tier 1 will take an evening. Nothing is locked — play them in any order.
Remove the thousands separators from a number: 1,234,567.89 becomes 1234567.89.
Turn snake_case into kebab-case: user_first_name becomes user-first-name.
Match "error" in any mix of upper and lower case.
Match any string that contains the word "regex".
Match strings containing "a.b" — with a real full stop between them.