code: func FindFirstControl(parent Control, fn func(Control) bool) Control {
  	linear := getLinearControlList(parent, fn)
  	if len(linear) == 0 {
  		return nil
  	}
  
  	return linear[0]
  }
docs: // FindFirstControl returns the first child for that fn returns true.
  // The function is used to find active or tab-stop control