code: public function renderElementFormGroup($sElementContent, $sRowClass, $sFeedbackElement = '' )
      {
          if (!is_string($sElementContent)) {
              throw new \InvalidArgumentException('Argument "$sElementContent" expects a string, "' . (is_object($sElementContent) ? get_class($sElementContent) : gettype($sElementContent)) . '" given');
          }
          if (!is_string($sRowClass)) {
              throw new \InvalidArgumentException('Argument "$sRowClass" expects a string, "' . (is_object($sRowClass) ? get_class($sRowClass) : gettype($sRowClass)) . '" given');
          }
          if ($sFeedbackElement && !is_string($sFeedbackElement)) {
              throw new \InvalidArgumentException('Argument "$sFeedbackElement" expects a string, "' . (is_object($sFeedbackElement) ? get_class($sFeedbackElement) : gettype($sFeedbackElement)) . '" given');
          }
          if( $sFeedbackElement ){
              $sElementContent .= '<i class="' . $sFeedbackElement . ' form-control-feedback"></i>';
          }
          return sprintf(static::$formGroupFormat, $sRowClass, $sElementContent) . "\n";
      }
docs: @param string $sElementContent
  @param string $sRowClass
  @param string $sFeedbackElement A feedback element that should be rendered within the element, optional
  
  @return string
  @throws \InvalidArgumentException