Item system data from where to get the supplements.
Actor document to which add the items.
OptionalnewLevel: number = 0New level, after the change.
Optionaloptions: { event?: "create" | "update" | "delete" } = {}Additional options
Optionalevent?: "create" | "update" | "delete"Relevant event.
Delete class associations on level change.
Called from ItemBasePF._onXOperation functions.