score:1

Accepted answer

If you switch on the split parameter of the tooltip, then it's divided for two parts, namely the point and header. In the documentation, you can find both of the formatters here: https://api.highcharts.com/highstock/tooltip.headerFormat, https://api.highcharts.com/highstock/tooltip.pointFormat . Additionally, here is the example code of formatting the "element marked with red":

tooltip: {
  split: true,
  headerFormat: '<span>It is tooltip header - {point.key}</span>'
}

Live example: http://jsfiddle.net/0eqmv7sw/

score:0

It's a tooltip but with the default option split : true - API Doc

With split : false you will see just the "default" tooltip

    tooltip:{
      enabled:true,
      split:false
    },

Fiddle

Edit :

If you are looking for the vertical line too it's xAxis.crosshair - API Doc


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