anchor.diff:      _selection.clear();
     }
   
  -  get selection =>
  +  dynamic get selection =>
         multi ? _selection : _selection.isNotEmpty ? _selection[0] : null;
   
     bool isSelected(inItem) => _selection.contains(inItem);
   
  -  void setItemSelected(inItem, inIsSelected) {
  +  void setItemSelected(Element inItem, bool inIsSelected) {
       if (inItem != null) {
         if (inIsSelected) {
           _selection.add(inItem);
  
positive.code:     }
    }
  
    void select(inItem) {
      if (multi) {
        toggle(inItem);
      } else if (selection != inItem) {
  
negative.code: // license that can be found in the LICENSE file.
  
  library spark_widgets.selection;
  
  import 'dart:html';
  
  import 'package:polymer/polymer.dart';
  
  