code: public function toNode(DOMDocument $document = null)
      {
          if (null === $document) {
              $document = new DOMDocument();
          }
  
          $node = $document->createElement('UPSFiled');
  
          $poa = $this->getPOA();
          if (isset($poa)) {
              $node->appendChild($poa->toNode($document));
          }
  
          return $node;
      }
docs: @param null|DOMDocument $document
  
  @return DOMElement