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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.
To add on, I think it's also because the pair of brackets will only be replaced with "" if the open and close brackets are in the correct order, of the same type as well as next to each other, on each iteration. By the last iteration, it should give you a "" if the bracket orderings are valid.
It's regex knowledge rather than code knowledge.
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