Everything on this page travels at the speed of the scroll.
Except one layer, which travels at half of it — and carries two children that do nothing.
A tall band with a position: sticky rail, which is stationary while the band
passes and therefore looks exactly like something moving against the scroll. It is not
marginalia and must not be counted.
Bands of real depth, so the container has somewhere to walk.
The census must name the layer.
And nothing else — not its two children, not the sticky rail.