code: func GetStackOrchestrator(flagValue, contextValue, globalDefault string, stderr io.Writer) (Orchestrator, error) {
  	// Check flag
  	if o, err := normalize(flagValue); o != orchestratorUnset {
  		return o, err
  	}
  	// Check environment variable
  	env := os.Getenv(envVarDockerStackOrchestrator)
  	if env == "" && os.Getenv(envVarDockerOrchestrator) != "" {
  		fmt.Fprintf(stderr, "WARNING: experimental environment variable %s is set. Please use %s instead\n", envVarDockerOrchestrator, envVarDockerStackOrchestrator)
  	}
  	if o, err := normalize(env); o != orchestratorUnset {
  		return o, err
  	}
  	if o, err := normalize(contextValue); o != orchestratorUnset {
  		return o, err
  	}
  	if o, err := normalize(globalDefault); o != orchestratorUnset {
  		return o, err
  	}
  	// Nothing set, use default orchestrator
  	return defaultOrchestrator, nil
  }
docs: // GetStackOrchestrator checks DOCKER_STACK_ORCHESTRATOR environment variable and configuration file
  // orchestrator value and returns user defined Orchestrator.