This field will allow you to customize the layout of your tooltip (highlighted below). In the example below we've inputted {{{defaultTooltipDescription}}} </br> {{discountDetails} </br> {{{prepaidDetails}}}.
{{{defaultTooltipDescription}}} corresponds to the text found in the Default Tooltip Description field.
{{discountDetails} corresponds to the text found in the Prepaid Plan Description on tooltip field.
{{{prepaidDetails}}} corresponds to the text found in the Discount Tier explanation on tooltip field.
</br> is simply a line break, to help space out the text and make it more readable.