Item system data from where to get the supplements.
Actor document to which add the items.
OptionalcurLevel: number = 0Current level, before the change.
OptionalnewLevel: number = 0New level, after the change.
Optionaloptions: { associatedClass?: string } = {}Additional options
OptionalassociatedClass?: stringValue for system.class on the items to add if needed.
Add class associations on level change.
Called from ItemBasePF._onXOperation functions.