Required Fields in a Datapack

Looking for help identifying what the reserved or required keys are in a datapack file. I see patterns across different mods and minecraft, but I'm not sure which ones are required or not. 1. Is "type": "modid:type" required? 1a. Does it have to be at the top of the file? 2. If I'm entering an item reference, does it have to have a key of "item" json "catalyst": { "item": "minecraft:bottle" } versus json "catalyst": "minecraft:bottle" Any other context around "magic" or "reserved" keys would be really helpful