Calculate Name for a New Node

Summary:

We are looking for a way to automatically assign the next available numeric value as the node name when a new node is created under a specific parent (e.g., 10Y) — without using a sequence property, due to concerns about it getting out of sync.

If we add a new node under 10Y, I want it to take the next available number (e.g., 1000–1010 are in use, so it should use 1011).

An error we keep receiving is : "Derived properties may only be referenced from node, parent, and ancestor scopes."