$ perl -MXML::LibXML -E'
   my $foster_home = XML::LibXML::Document->new("1.0", "UTF-8");
   my $node;
   {
      my $xml = "<root><foo><bar/></foo></root>";
      my $doc = XML::LibXML->new->parse_string($xml);
      ($node) = $doc->findnodes("//bar");
      $node->setOwnerDocument($foster_home);
   }
   {
      my $doc = $node->ownerDocument;
      say "owner=", $doc;
      if ($doc) { say $_->nodeName for $doc->findnodes("//*"); }
   }
'
owner=XML::LibXML::Document=SCALAR(0x832af38)