DROPDOWN
Changes the appearance of the list for the user: only the selected item is shown beside a button with an arrow pointing down. To select another option, the user must press this button, which displays all items in the list.
Value
"YES" or "NO".
Default: "NO"
Notes
This attribute is ignored for multiple lists (MULTIPLE=YES).
This attribute is only consulted when the dialog is first mapped (IupMap, IupShow, IupShowXY or IupPopup). After such, it cannot be changed.