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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.
they join the elements in the array without spaces
if you wanted to join all the elements with commas between them you'd use .join(', ')
The ones that invoke the map method?
What does the parentheses do in front of the join ?