Is it possible to prevent node from being dropped before specific node at top level? This is possible for non-top level node since nextParent with latest state of children will be passed to canDrop callback. For top level node, nextParent is null and I can't figure way to get latest state of tree. Without latest state of tree, how can I tell in front of which node it's being dropped?

Example (How to prevent PF 1 and PF 2 from being dropped before SF 1 & SF 2?)

SF 1
--SF 1.1
----SF 1.1.1
SF 2
--SF 2.1
PF 1
PF 2