Add a node id to LOCATABLE so that child objects can be uniquely identified without relying on the name field. This would enable paths to be constructed to any object in data. The original idea was sibling_id an integer unique just across sibling child nodes. This would enable unique runtime path formation in a regular way, regardless of the type of RM class, as long as it inherits from LOCATABLE. In theory, the uid field could be used, but this creates a real overhead of GUIDs in storage and in paths which is arguably too heavy.