foreach my $child ($tag->children) {
  my $newElt= XML::Twig::Elt->new(Contains => { map {$_ , $child->{'att'}->{$_}||''} qw(name type comment) });
  $tag->paste('last_child', $newElt);
}

##</code><code>##

cannot paste an element that belongs to a tree at ./E2W line 546