A lot of people commenting about "an index into an array is also a pointer", I thought people commonly referred to integer indexes of this kind as handles, or index-handles? (like in this article [1]).

This way of representing trees reminds me of two classic data structures: heaps [2] and disjoint-sets [3].

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1: https://floooh.github.io/2018/06/17/handles-vs-pointers.html

2: https://en.wikipedia.org/wiki/Heap_(data_structure)

3: https://en.wikipedia.org/wiki/Disjoint-set_data_structure