This page refers to all enumerated lists, with the exception of multi-valued lists.
Enumerated lists are fields with display types of List, Popup, Radio Button, Checkbox, User and Tab.
The three principal abilities of rules with enumerated lists are to set a value in the list, to change a value in the list and to remove the value from the list. Adding a value and changing the value in the list are accomplished with the same assignment:
MY_LIST = 'Valid value';
The value you assign within the rule must exist, else the rules will not compile.
If you want to remove the value in the list assign it a null value as follows:
MY_LIST = '{null}';
