[gtkada] Event handlers question

[Grein, Christoph]

I have defined an entry for text input with Glade and this is the generated Ada 
code.

  procedure On_Entry_Changed (Object: access Gtk_Entry_Record'Class) is
  begin
    ...
  end On_Entry_Changed;

  function On_Entry_Focus_Out_Event (Object: access Gtk_Widget_Record'Class;
                                     Params: in     Gtk.Arguments.Gtk_Args)
                                             return Boolean
  is
    Arg1: Gdk_Event := To_Event (Params, 1);
  begin
    ...
    return False;
  end On_Entry_Focus_Out_Event;

Please can somebody explain to to me why for change events a procedure is 
generated, for focus out events a function.
What is the use of Params and Arg1?
Which is the use of the Boolean return value, i.e. what happens if True is 
returned, what if False is returned?

I have found no clue by reading the GtkAda RM.