The cursor extension (like cross hair) should go from the top of the plot to the bottom, and from the left of the plot to the right.

We should be able to turn the cursor off and on.

The cursor mentioned here can be found for reference in highchart:
http://api.highcharts.com/highcharts/xAxis.crosshair

Example here: http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/tooltip/crosshairs-x/