It can be in order, or at random based on weights.
How to define a list placeholder:
plugins/Gunging_Ootilities_Plugin/list-placeholders.yml
WhateverNameYouWant:
- Text [weight]
- Text [weight]
- Text [weight]
...
If the list has at least one space, and it ends in a value that parses as an integer value, that will be considered the weight.