code: func (precondition *ScalePrecondition) ValidateReplicationController(controller *api.ReplicationController) error {
  	if precondition.Size != -1 && controller.Spec.Replicas != precondition.Size {
  		return PreconditionError{"replicas", strconv.Itoa(precondition.Size), strconv.Itoa(controller.Spec.Replicas)}
  	}
  	if len(precondition.ResourceVersion) != 0 && controller.ResourceVersion != precondition.ResourceVersion {
  		return PreconditionError{"resource version", precondition.ResourceVersion, controller.ResourceVersion}
  	}
  	return nil
  }
docs: // ValidateReplicationController ensures that the preconditions match.  Returns nil if they are valid, an error otherwise