anchor.diff:  // http://www.polymer-project.org/. 
   library polymer_ui_elements.polymer_ui_submenu_item;
   
  -import 'dart:html' show Element;
  +import 'dart:async' show Stream;
  +import 'dart:html' show CustomEvent, Element, EventStreamProvider;
   import 'package:polymer/polymer.dart' show CustomTag, PolymerElement, published;
   import 'package:logging/logging.dart' show Logger;
   import 'package:polymer_ui_elements/polymer_ui_menu_item/polymer_ui_menu_item.dart' show PolymerUiMenuItem;
   import 'package:polymer_ui_elements/polymer_ui_menu/polymer_ui_menu.dart' show PolymerUiMenu;
  -//import 'package:polymer_elements/polymer_selector/polymer_selector.dart' show PolymerSelector;
   
   /**
    * polymer-ui-submenu-item is a menu-item that can contains other menu-items.
  
positive.code:   
    bool collapsed = true;
    
    List<Element> get items {
      return (this.$['menu'] as PolymerUiMenu).items;
    }
  
negative.code:     if (this.hasItems() && this.active) {
        this.collapsed = !this.collapsed;
        this.unselectAllItems();
        dispatchEvent(new CustomEvent('polymer-select', detail: {'isSelected': true, 'item': this}));
      }
    }
    
  