[jve]

Well, only if your UI allows dragging two items at once. If you reorder multiple items, well, I suppose you can resolve it by passing some relative position. If you want to squeeze something in-between reordered items, then -1 probably is not a good choice, but more like calculating some middle value between previous and next item.

[grzm]

What would the timestamp represent? Are you providing a timestamp which encodes the position somehow, or using CURRENT_TIMESTAMP? Updating the timestamp for all of the rows in the (sub) list? How does this permit you to reorder the items in the list?

[jve]

I haven't implemented this, just brainstorming.

Timestamp would only represent position and enables to put something in between, rather than an integer which adds +1. If put A (timestamp = 100) between B (timestamp = 200) and C (timestamp = 300), just set that order value to middle (150). Naive

It actually looks the same as "What about leaving room?" and, yeah, introduces complexity when you organize items for too long.