These are keys which trigger upon a trainer using an item from their inventory.
"BeforeItemUse"Triggers when a trainer chooses to use an item, but before the effects of that item are actually executed.
"AfterItemUse"Triggers after the effects of a trainer's used item are executed.
Trigger Extensions: You may extend these keys with an item ID to specify that they should only trigger when a specific item is used. For example, "BeforeItemUse_POTION" would trigger only when a trainer is about to use a Potion.