How many children each node has (whether they show or not).
collapsed
readonly
Uint8Array
1 where the node is collapsed: it has children and they are folded away.
parent
readonly
Int32Array
Each node's parent in the tree, -1 for a root.
x
readonly
Float64Array
Where the layout put every node, in linear coordinates, the hidden ones included: each sits on its nearest ancestor that shows, which is where it folds into and unfolds from.