declaredBaseItems

Java base items that installed plugins assign to their item models, keyed by item model id (namespace:path) with minecraft:<item> values. The pack alone cannot tell which item an item_model rides on, but the plugin config that creates the item can: Oraxen's material: puts oraxen:tomato on minecraft:apple. These bases are added to the filename heuristic's choice, like the rspm_item_bases files a producer ships in its own pack. Only the backend can read those configs, so the default declares nothing.