anchor.diff:              hover.datum = datum;
             }
           });
  +        rect.onClick.listen((MouseEvent evt) {
  +          var sel = selectElement(evt.target);
  +          Object datum = sel.datum;
  +          _onItemClick.signal(datum);
  +        });
         }
         
         $elmt.onMouseLeave.listen((_) {
  
positive.code: part of D3Dart;
  
  abstract class ChartWithAxes {
    num width;
  
negative.code: }
  
  class ColumnChart extends ChartWithAxes {
    
    final EventStream<Object> _onItemClick = new EventStream<Object>();
    Stream<Object> get onItemClick => _onItemClick.stream;
    
    Element $elmt;
    
  