HolderSet

Holder sets can represent any registry type, ie. block, item, entity. Holder sets can be formatted in 3 ways.

Single

A single is a string referencing the single registry entry you would like to use.

{
    "holderSet": "minecraft:stick"
}

Tag

This way to format references a tag, all tag references must start with a pound symbol or hashtag.

{
    "holderSet": "#minecraft:planks"
}

List

Lists can be used to reference multiple registry entries without having to make a tag.

{
    "holderSet": [
        "minecraft:stick",
        "minecraft:stone"
    ]
}