code: func validateCommonFields(obj, old runtime.Object) (field.ErrorList, error) {
  	allErrs := field.ErrorList{}
  	objectMeta, err := api.ObjectMetaFor(obj)
  	if err != nil {
  		return nil, fmt.Errorf("failed to get new object metadata: %v", err)
  	}
  	oldObjectMeta, err := api.ObjectMetaFor(old)
  	if err != nil {
  		return nil, fmt.Errorf("failed to get old object metadata: %v", err)
  	}
  	allErrs = append(allErrs, validation.ValidateObjectMetaUpdate(objectMeta, oldObjectMeta, field.NewPath("metadata"))...)
  
  	return allErrs, nil
  }
docs: // TODO: add other common fields that require global validation.