code: function () {
  		var series = this,
  			chart = series.chart,
  			hoverSeries = chart.hoverSeries;
  
  		if (!hasTouch && chart.mouseIsDown) {
  			return;
  		}
  
  		// set normal state to previous series
  		if (hoverSeries && hoverSeries !== series) {
  			hoverSeries.onMouseOut();
  		}
  
  		// trigger the event, but to save processing time,
  		// only if defined
  		if (series.options.events.mouseOver) {
  			fireEvent(series, 'mouseOver');
  		}
  
  
  		// bring to front
  		// Todo: optimize. This is one of two operations slowing down the tooltip in Firefox.
  		// Can the tracking be done otherwise?
  		if (series.tracker) {
  			series.tracker.toFront();
  		}
  
  		// hover this
  		series.setState(HOVER_STATE);
  		chart.hoverSeries = series;
  	}
docs: Series mouse over handler