The history of user actions is stored in QuietTreeManager.HistoryComponent. It is a stack of JSON objects containing data for undo and redo actions. An actor is stored in the history as GUID to avoid missing references when the actor is destroyed.
The component is fully encapsulated and provides several public methods for working with history.
You can add your action to the history using an actor only.
Add QuietActorsInterface to your actor class:
