public function setContentType($string = '')
 {
     if (in_array($string, $this->allowed_types) == TRUE || preg_match('(^[a-zA-Z0-9]+/[a-zA-Z0-9]+$)', $string) > 0) {
         return parent::setVar($string, 'type', 'string');
     }
     // end if
     return FALSE;
 }