I have a perl Gtk2 app that uses gtk_widget_set_events():
    my $b = Gtk2::EventBox->new;
    $b->set_events('pointer_motion_mask');

However, with Gtk3, I got:
 Argument "pointer_motion_mask" isn't numeric in subroutine entry at
         /usr/lib/perl5/vendor_perl/5.18.1/x86_64-linux-thread-multi/Glib/Object/Introspection.pm line 59 (#6)

GdkEventMask is a bitfield in Gdk

This suggests that gtk+ is missing overrides for gtk_widget_set_events()
and _add_events() that tell gobject introspection that the "events"
argument is actually of type GdkEventMask.

As a workaround, I'm forced to create an event mask with
Gtk3::Gdk::EventMask->new ("pointer_motion_mask") and then dereference
it to get at the corresponding integer:

    my $b = Gtk3::EventBox->new;
    $b->set_events(${ Gtk3::Gdk::EventMask->new ("pointer_motion_mask") });

This violates encapsulation!