Sorry everyone, I didn't notice that the <table> was our custom template for the tooltip, so the problem can be easily solved by specifying a different template not breaking W3C validation. So you can ignore this request.

Regards and sorry for the "false alarm"

When mouse hovering chart points, a tooltip is generated, which has the following DOM (this example has 1 X axis and 2 Y axes): <div class="highcharts-label highcharts-tooltip highcharts-color-undefined" style="position: absolute; left: 135px; top: -9999px; opacity: 0; pointer-events:...