id = $id;
    return $this;
  }
  /**
   * Set the label
   * @chainable
   */
  public function label($label) {
    $this->label = $label;
    return $this;
  }
  /**
   * Set the url
   * @chainable
   */
  public function url($url) {
    $this->url = $url;
    return $this;
  }
}
/**
 * Menu element that provides a link to a new page.
 */
class Menu_Element_Link extends Menu_Element {
  public function __toString() {
    return "
";
  }
}
/**
 * Menu element that provides a pop-up dialog
 */
class Menu_Element_Dialog extends Menu_Element {
  public function __toString() {
    return "";
  }
}
/**
 * Root menu or submenu
 */
class Menu_Core extends Menu_Element {
  public $elements;
  public $is_root;
  /**
   * Return an instance of a Menu_Element
   * @chainable
   */
  public static function factory($type) {
    switch($type) {
    case "link":
      return new Menu_Element_Link();
    case "dialog":
      return new Menu_Element_Dialog();
    case "submenu":
      return new Menu();
    default:
      throw Exception("@todo UNKNOWN_MENU_TYPE");
    }
  }
  public function __construct($is_root=false) {
    $this->elements = array();
    $this->is_root = $is_root;
  }
  /**
   * Add a new element to this menu
   */
  public function append($menu_element) {
    $this->elements[$menu_element->id] = $menu_element;
    return $this;
  }
  /**
   * Retrieve a Menu_Element by id
   */
  public function get($id) {
    return $this->elements[$id];
  }
  public function __toString() {
    $html = $this->is_root ? "";
    return $html;
  }
}