code: func (d Data) Pages() Pages {
  	v, found := d["pages"]
  	if !found {
  		return nil
  	}
  
  	switch vv := v.(type) {
  	case Pages:
  		return vv
  	case func() Pages:
  		return vv()
  	default:
  		panic(fmt.Sprintf("%T is not Pages", v))
  	}
  }
docs: // Pages returns the pages stored with key "pages". If this is a func,
  // it will be invoked.