By default, the items displayed on the Timeline are unordered. They are stacked in the order that they where loaded. This means that way items are stacked can change while moving and zooming the Timeline.
To display and stack the items in a controlled order, you can provide a
custom sorting function via the configuration option order.
This is only suitable for relatively small amounts of items, as it forces
the Timeline to order and re-stack all items with every redraw.