The list of entries that appear in a COMBOBOX can be populated programmatically. That is rather than defining a static list using the ITEMS attribute, you can populate it at runtime via 4gl code. This can use the INITIALIZER syntax in the form file to indicate what function to use to populate the ComboBox item list when the form is loaded.
There is an error that can occur when using INITIALIZER due to an optimisation process at link time for which there are some simple solutions.
Read more at
https://4js.com/ask-reuben/ig-164/