Help with Callback syntax to add input element and reference the parent element of the Callback

[Ascariel1984]

It would be nice if someone can help me out withe Callout syntax. I know how to use the Dice Callback to directly have access to the property value of the current field. But I cannot figure out how to do this for the regular Callback. Additionally I would like to add a checkbox with the Callback function.

Summary:

1. How to reference current element of Callback function, like the property/value (Example: Fate: 3, then how to get '3')
2. How to add an element with a Callback function?

I tried:
const checkbox = document.createElement('input');
checkbox.type="checkbox";
checkbox.id="some-id";
checkbox.name="some-name";
var item = document.getElementsByClassName("fate");
item.appendChild(checkbox)

I want to do this to add e.g. 3 checkboxes to the Fate property line, so I can track how many points I have left (Fate: 3 [x] [x] [x])