code: function _onDblclick(d) {
    var event = d3.event,
        node = event.target;
  
    node = node.correspondingUseElement || node;
  
    if(_scheduledClickId) {
      clearTimeout(_scheduledClickId);
      _scheduledClickId = 0;
    }
  
    switch(_getType(node)) {
      case "io":
        d.toggleAdditionalInclusion();
        _update();
      break;
    }
  }
docs: Double click event handler.
  @param d {DataNode} Data of the clicked element