directive @tag(name: String!) repeatable on
  | FIELD_DEFINITION
  | INTERFACE
  | OBJECT
  | UNION

extend type Product @key(fields: "upc") {
  upc: String! @external
  weight: Int @external
  price: Int @external
  inStock: Boolean @tag(name: "private")
  shippingEstimate: Int @requires(fields: "price weight")
}