Menus (covered in Creating Menus) can have components that are also choices. These components are groups of items that have an interaction upon selection just like other choices. The :interaction keyword is used to associate radio or check buttons with the group — with the values :single-selection and :multiple-selection respectively. By default, a menu component has an interaction of :no-selection.
See Grouping menu items together for more details.
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015