code: func (o *RuntimeOpt) Set(val string) error {
  	parts := strings.SplitN(val, "=", 2)
  	if len(parts) != 2 {
  		return fmt.Errorf("invalid runtime argument: %s", val)
  	}
  
  	parts[0] = strings.TrimSpace(parts[0])
  	parts[1] = strings.TrimSpace(parts[1])
  	if parts[0] == "" || parts[1] == "" {
  		return fmt.Errorf("invalid runtime argument: %s", val)
  	}
  
  	parts[0] = strings.ToLower(parts[0])
  	if parts[0] == o.stockRuntimeName {
  		return fmt.Errorf("runtime name '%s' is reserved", o.stockRuntimeName)
  	}
  
  	if _, ok := (*o.values)[parts[0]]; ok {
  		return fmt.Errorf("runtime '%s' was already defined", parts[0])
  	}
  
  	(*o.values)[parts[0]] = types.Runtime{Path: parts[1]}
  
  	return nil
  }
docs: // Set validates and updates the list of Runtimes