There's no way in Forge right now to see the actual priority values, but the children will be sorted correctly.
If what you want is to sort items in reverse-chronological-order, I'd suggest simply setting the priority to a normal timestamp (or using push -- it orders them automatically). You can then simply render them backwards to achieve the reverse order you want. For example, rather than appending new messages to the bottom of a list in your app, you could insert them before the first element.