How to add text that will show on hovering over the bars

Problem:
My requirement is to add a prefix text on hover, but only the default values are displaying in the tool-tip.

Solution:
To pull that off, you need to make use of custom tokens. The custom token is defined in the plot or series object as an attribute or array using the "data" prefix, e.g., data-fullname or data-extracredit. It is then recalled in the tooltips, value boxes, or crosshair plot labels, e.g., %data-fullname or %data-extracredit. Please use this demo for reference.