code: function (selected) {
  		var series = this;
  		// if called without an argument, toggle
  		series.selected = selected = (selected === UNDEFINED) ? !series.selected : selected;
  
  		if (series.checkbox) {
  			series.checkbox.checked = selected;
  		}
  
  		fireEvent(series, selected ? 'select' : 'unselect');
  	}
docs: Set the selected state of the graph
  
  @param selected {Boolean} True to select the series, false to unselect. If
  UNDEFINED, the selection state is toggled.