Display custom tooltip between two sets of points

Hi everyone,

I am trying to get the result as shown below, for the blue trace : I want a special text div to appear between two sets of points :

I don’t know where to get started.
I tried using the tooltip and making it persistent -> couldn’t make it work
Also, tried using the hoverinfo -> same

How could I achieve this ?

Example https://plot.ly/javascript/hover-events/#coupled-hover-events should help get started.

Thank you Etienne. Still, the resource you gave me is not really understandable. For example, I don’t know how to style what is displayed.
Also, I don’t want this text to appear on hover, but be persistent at any time over the blue trace.

Edit: I found out about annotations. Could you link me to the official, complete documentation ? The one I found online seems incomplete.