code: func Revision(obj runtime.Object) (int64, error) {
  	acc, err := meta.Accessor(obj)
  	if err != nil {
  		return 0, err
  	}
  	v, ok := acc.GetAnnotations()[RevisionAnnotation]
  	if !ok {
  		return 0, nil
  	}
  	return strconv.ParseInt(v, 10, 64)
  }
docs: // Revision returns the revision number of the input object.