code: public function cloneChildrenFrom(SimpleXMLElement $src, $deep = true)
      {
          $src = dom_import_simplexml($src);
          $dst = dom_import_simplexml($this);
          $doc = $dst->ownerDocument;
  
          $fragment = $doc->createDocumentFragment();
          foreach ($src->childNodes as $child) {
              $fragment->appendChild($doc->importNode($child->cloneNode($deep), $deep));
          }
          $dst->appendChild($fragment);
  
          return $this;
      }
docs: Clone all children from a node and add them to current node
  
  This method takes a snapshot of the children nodes then append them in order to avoid infinite
  recursion if the destination node is a descendant of or the source node itself
  
  @param    SimpleXMLElement $src Source node
  @param    bool $deep If TRUE, clone descendant nodes as well
  @return    SimpleDOM                    Current node