GtkMenuShell::select_item
    
     select_item()  is largely
     used internally.  A 'selected' item is displayed in the prelight
     state and has its submenu popped up, if it has one.  This is also
     achieved by using the mouse pointer or arrow keys in an active
     GtkMenu, and should not be confused with
     the "activate" signal, which
     is triggered by mouse clicks or the Enter key.
    
    
     Using this method causes the designated item to emit the 
     "select" signal, which in turn
     triggers the 'selected' state.