Constant ITEM_ITEMS 

pub const ITEM_ITEMS: ItemCapabilityKey<dyn ResourceHandler<ItemResource>>;

Items held by an item, as NeoForge 26.3’s Capabilities.Item.ITEM: a handler for the item at one place, whose changes rewrite the item there with an exchange of one, so from a stack of more than one the changed item splits off. The game answers it for an item with item_container slots, kept in its minecraft:container.