code: func (f *Form) AddDropDown(label string, options []string, initialOption int, selected func(option string, optionIndex int)) *Form {
  	f.items = append(f.items, NewDropDown().
  		SetLabel(label).
  		SetCurrentOption(initialOption).
  		SetOptions(options, selected))
  	return f
  }
docs: // AddDropDown adds a drop-down element to the form. It has a label, options,
  // and an (optional) callback function which is invoked when an option was
  // selected. The initial option may be a negative value to indicate that no
  // option is currently selected.