OldFormat

items_data.json:

To set bauble's type/types:

{
  "minecraft:elytra": {
    "types": [
      "baubles:body",
      "baubles:elytra"
    ]
  }
}

To make an item not a bauble:

{
  "minecraft:elytra": {
    "addition": "remove"
  }
}

types_data.json:

To set a new type:

{
  "baubles:elytra": {
    "name": "elytra",
    "amount": 1,
    "priority": 5,
    "parent": [
      "baubles:body"
    ]
  }
}