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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.
@CoolHacker 023 is a viable number prefix.
And what if those three digits \d{3} start with 0, like 023? The number must be not valid in that case.
Could someone explain this code to me?