code: func CheckCodec(c Codec, internalType Object, externalTypes ...schema.GroupVersionKind) error {
  	if _, err := Encode(c, internalType); err != nil {
  		return fmt.Errorf("Internal type not encodable: %v", err)
  	}
  	for _, et := range externalTypes {
  		exBytes := []byte(fmt.Sprintf(`{"kind":"%v","apiVersion":"%v"}`, et.Kind, et.GroupVersion().String()))
  		obj, err := Decode(c, exBytes)
  		if err != nil {
  			return fmt.Errorf("external type %s not interpretable: %v", et, err)
  		}
  		if reflect.TypeOf(obj) != reflect.TypeOf(internalType) {
  			return fmt.Errorf("decode of external type %s produced: %#v", et, obj)
  		}
  		if err = DecodeInto(c, exBytes, internalType); err != nil {
  			return fmt.Errorf("external type %s not convertible to internal type: %v", et, err)
  		}
  	}
  	return nil
  }
docs: // CheckCodec makes sure that the codec can encode objects like internalType,
  // decode all of the external types listed, and also decode them into the given
  // object. (Will modify internalObject.) (Assumes JSON serialization.)
  // TODO: verify that the correct external version is chosen on encode...