XML : How can I inject HTML code via DOM / XML

got an HTML and Need to inject a new element. Actually I inject it by DML/XML and xPath, but cannot get it into my original...

Example:

  public function render(){      $resultArray = parent::render();      $doc = new \DOMDocument();      $doc->loadHTML($resultArray['html']);      $xpath = new \DOMXPath($doc);      $elements = $xpath->query("//*[@class=\"inp-grp\"]");      $container = $doc->importNode(new \DOMElement('div'));      $container->textContent = 'myNewContainer';      foreach($elements as $element){          $element->appendChild($container);      }      // original is not manipulated...       // How to put my manipulated Element into it?       $resultArray['html'] = $doc->saveHTML();      return $resultArray;  }    

Regards n00n