Item_Shield: {
    type: "compound";
    value: {
        tag?: {
            type: "compound";
            value: {
                Base: { type: "int"; value: number };
                Patterns?: {
                    type: "list";
                    value: {
                        type: "compound";
                        value: {
                            Color: { type: "int"; value: number };
                            Pattern: { type: "string"; value: string };
                        }[];
                    };
                };
            };
        };
    };
} & Item_ItemStack

Additional fields for shield.