add category label mouse events
Events triggered when a user clicks/hovers/etc a category label (xAxis labels).
I would use this to provide more in depth information about the label clicked. For instance, charting years in xAxis, user clicks 2012, should bring up a menu with additional options for that year
Implemented by Black Label's plugin, Custom-Events: http://www.highcharts.com/plugin-registry/single/15/Custom-Events