Hope you understand the basics of the Highcharts tooltips. Highcharts has a shared tooltip option but it will be shared on all points. What if you want to have a shared tooltip only when points are overlapping? There is no such an option in Highcharts to get a shared tooltip only when the points are overlapping.
Below I have shown a work-around to get a shared tooltip only when the points overlap (graphs intersect).
This article is going to talk about the tooltip shape feature in the Highcharts version 4 (And what are the available values for shape parameter). In early Highcharts versions tooltip shape is always rectangular. With this new feature, user can choose between few shapes that are defined in Highcharts. At the same time user can add new paths to the collection as functions. I haven’t done it so not going to talk about custom shapes.