Where can I find the layout maps for the variety of options when working with "Layout of numeric keypad?"

I set up my keyboard to have a "compose" key on my Ubuntu 21.04 system. I love the flexibility! When exploring (System Settings-Hardware-Input Devices-Keyboard-Advanced), I discovered the Layout of numeric keypad selection. There are options there like ATM/phone-style, Hexadecimal, Unicode additions, etc.

I am very interested in both the Hexadecimal and the Unicode additions... However, I have not been able to find the layout mapping in order to choose whether to have a new keypad layout or leave it alone.

Where does one find the reference material for this feature?

UPDATE I am reviewing this questin (How to set up a custom keyboard layout?) and its answer. While not exactly the same question, they are related. If I glean a solution while perusing that question, I'll post it here.