Some Eden editor dialogues provide option to choose an item from a list of possible items that open in a drop down list (I think it is called a RscCombo list) when either the currently selected item or the adjacent drop down arrow are clicked with LMB.

OBS:
When the list opens, the user is unable to click on any item in the list (clicking does nothing).
The user can successfully select items using up/down arrows an enter key on keyboard.

EXP:
User should be able to select items with the mouse.