code: func (m *Modal) SetDoneFunc(handler func(buttonIndex int, buttonLabel string)) *Modal {
  	m.done = handler
  	return m
  }
docs: // SetDoneFunc sets a handler which is called when one of the buttons was
  // pressed. It receives the index of the button as well as its label text. The
  // handler is also called when the user presses the Escape key. The index will
  // then be negative and the label text an emptry string.