private static function dumpControlError(IFormControl $control)
 {
     if (!$control->hasError()) {
         return '';
     }
     if ($control instanceof FormControlSet && $control->hasError(FormControlError::WRONG)) {
         $message = '<ul>';
         foreach ($control as $innerControl) {
             $message .= self::dumpControlError($innerControl);
         }
         $message .= '</ul>';
     } else {
         $message = $control->getErrorMessage();
     }
     return '<li>' . $control->getName() . (($label = $control->getLabel()) ? " ({$label})" : '') . ' is ' . $control->getError() . ': <i>' . $message . '</i></li>';
 }