docs: func (s *UpdateStackInstancesInput) Validate() error {
  	invalidParams := request.ErrInvalidParams{Context: "UpdateStackInstancesInput"}
  	if s.Accounts == nil {
  		invalidParams.Add(request.NewErrParamRequired("Accounts"))
  	}
  	if s.OperationId != nil && len(*s.OperationId) < 1 {
  		invalidParams.Add(request.NewErrParamMinLen("OperationId", 1))
  	}
  	if s.Regions == nil {
  		invalidParams.Add(request.NewErrParamRequired("Regions"))
  	}
  	if s.StackSetName == nil {
  		invalidParams.Add(request.NewErrParamRequired("StackSetName"))
  	}
  	if s.OperationPreferences != nil {
  		if err := s.OperationPreferences.Validate(); err != nil {
  			invalidParams.AddNested("OperationPreferences", err.(request.ErrInvalidParams))
  		}
  	}
  
  	if invalidParams.Len() > 0 {
  		return invalidParams
  	}
  	return nil
  }