What is the difference between 1st, 2nd, 3rd group in keywords list?

PeterJones

The UDL provides multiple keywords lists so that you can style different groups of keywords with different colors, similar to the way that the builtin lexers have multiple lists of keywords (like C has one style for commands like case and if, and a different style for data types like int and double)

read the docs: https://ivan-radic.github.io/udl-documentation/