sub _move {
    my $did_something = 0;
    foreach my $descendant ( $_[1]->descendants('slip') ) {
        $did_something++;

        $descendant->set_att('_TYPE' => 'produce');
        
        # Move the <slip> out of the <box> section
        #
        # This appears to be the problem, even though
        # this should never be reached in the second
        # document (no <slip> descendants)
        $descendant->move('before', $_[1]);
    }
    
    $_[1]->delete;
    $_[0]->flush() if $did_something;
    
    1;
}