code: func (c *RadioGroup) Selected() int {
  	selected := -1
  
  	for id, item := range c.items {
  		if item.Selected() {
  			selected = id
  			break
  		}
  	}
  
  	return selected
  }
docs: // Selected returns the number of currently selected radio
  // button inside the group or -1 if no button is selected