Item_ArmorTrim: {
    type: "compound";
    value: {
        tag?: {
            type: "compound";
            value: {
                Trim: {
                    type: "compound";
                    value: {
                        Material: { type: "string"; value: string };
                        Pattern: { type: "string"; value: string };
                    };
                };
            };
        };
    };
} & Item_ItemStack

Additional fields when an armor is [trimmed](https://minecraft.wiki/w/Smithing Template).