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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.
"the only thing that would actually meet that criteria is nested arrays." => Well, no. For instance, an array of string does the job just right.
One could also choose to represent a whole 2D matrix with just one string (i.e https://www.codewars.com/kata/586214e1ef065414220000a8 and other string input katas do exactly that). I'm not sure what makes you think something would be wrong.
No: