A List function that sets add mode in the list
#include <Xm/List.h> void XmListSetAddMode Widget widgetBoolean state
XmListSetAddMode allows applications control over Add Mode in the extended selection model. This function ensures that the mode it sets is compatible with the selection policy (XmNselectionPolicy) of the widget. For example, it cannot put the widget into add mode when the value of XmNselectionPolicy is XmBROWSE_SELECT.
For a complete definition of List and its associated resources, see XmList (3).