List attribute in a complex data type

In a multi line form I need to create an attribute that represents a list of options (to display in a select widget: Option1/Option2/Option3).
I’ve created a complex data type and managed to display it’s attributes in a multi-instantiated (“this widget can be duplicated”) group widget.
(I’m using Bonita Performance subscription).
I don’t know how to create an attribute in my custom data type, that could implement the list of options. The only avaliable data types when creating attributes are String, Int, Float, Long, Double, Boolean and Date.
Thanks.

Found the answer…
Must create a list option variable and then use it in the available values of my select widget (inside a multi-instantiated group).