Yes, this event is necessary since Highcharts will only replace the content in the `div` with class `chart` and the spinner is added to the `Chart` control's `$el` element which is a `div` with class `control` that is a parent of the `<div class=chart></div>` element that Highcharts writes to. I suppose we could write the loading icon to the Highchart's `<div class=chart></div>` if we wanted to but I have not tested if that will work or not. Let me know if you prefer that over subscribing to the event.