code: public function render(array $elements)
      {
          $formRowHelper = $this->getFormRowHelper();
          $labels = array();
          $markups = '';
          $totalSpanWidth = 0;
          foreach ($elements as $spanWidth => $element) {
              $elementErrors = $element->getMessages();
              $markup = $formRowHelper->render($element);
              if (preg_match('~<label.*</label>~isU', $markup, $match)) {
                  $labels[] = $match[0];
                  $markup = str_replace($match[0], '', $markup);
              } else {
                  //$labels[] = false;
              }
              $markups .= sprintf(
                  '<div class="col-md-%d%s">%s</div>',
                  $spanWidth,
                  empty($elementErrors) ? '' : ' input-error',
                  $markup
              );
              $totalSpanWidth += $spanWidth;
          }
          $labelSpanWidth = 12 - $totalSpanWidth;
          
          $labelMarkup = sprintf(
              '<div class="col-md-%d yk-label">%s</div>',
              $labelSpanWidth,
              implode(' / ', $labels)
          );
          
          $form_row_class = 'row';
          if ($this->layout == 'form-horizontal') {
              $form_row_class = 'form-group';
          }
          
          
          return sprintf(
              '<div class="controls controls-row ' . $form_row_class . '">%s%s</div>',
              $labelMarkup,
              $markups
          );
      }
docs: Utility form helper that renders a label (if it exists), an element and errors
  
  @param ElementInterface $elements
  @return string
  @throws \Zend\Form\Exception\DomainException