sub addAtt
  { my( $t, $elt, $parent)= @_; 
    my $e_parent = $elt->prev_elt($parent);
    if( !$e_parent) { die "no parent '$parent' for element '", $elt->gi, "'\n"; }
    $e_parent->set_att($elt->gi,$elt->att( 'att'));
    $elt->delete;
    $t->flush;            
}