The whole point of walking as a tree rather than listing addresses — 1,204,880 beside
Model!O30 is what makes the chain readable as a model rather than as a set of coordinates.
A formula node shows its expression too, because at that point the node explains itself.
Shared with the flat ICellRanges listing (renderRanges) for the same reason
describeNodeLabel is: the flat list is these rows without the hop structure, so the two
shapes cannot be allowed to drift into describing one member two ways.
A node's payload: the value for a single cell, the size for a range.