This is for sets of documents where orderings can be made regardless of the content, so not indexed on a known field but ordered. And not just a single ordering but multiple alternative orderings.
Imagine a box of cards, they're in a particular order first to last. To order them again requires going through each card and placing it in the new order, and the previous order is unavailable until it's reordered destroying the existing one again. The first solution was a separate document of a different type which had lists of orders, each list within the lists had a label or a name, and the ordering was a list of documents in a particular order.
This works but can only work after the documents have been selected and then the ordering applied. That means that all the other features of search or query only happen before the ordering can be applied. That makes bookmarking impossible and so the whole set has to be returned to the client and the client has to manage the paging. This is horrible.
The planned altern