public function authors()
 {
     $oxymel = new Oxymel();
     $authors = $this->export->authors();
     foreach ($authors as $author) {
         $oxymel->tag('wp:author')->contains->tag('wp:author_id', $author->ID)->tag('wp:author_login', $author->user_login)->tag('wp:author_email', $author->user_email)->tag('wp:author_display_name')->contains->cdata($author->display_name)->end->tag('wp:author_first_name')->contains->cdata($author->user_firstname)->end->tag('wp:author_last_name')->contains->cdata($author->user_lastname)->end->end;
     }
     return $oxymel->to_string();
 }