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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
I ran your code and it yields the error below. Tests have been updated since, do find a pattern in doing such exponentations.
Because your regex only matches when there is at least one letter after the apostroph.