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: class SparkSelection extends SparkWidget {
    @published bool multi = false;
  
    final List _selection = [];
  
    SparkSelection.created(): super.created();
  
  
negative.code:     }
    }
  
    void toggle(Element inItem) {
      setItemSelected(inItem, !isSelected(inItem));
    }
  }
  