code: protected function buildFatal()
      {
          $haveFatal = isset($this->stats['counts']['fatal']);
          if (!$haveFatal) {
              return '';
          }
          $lastError = $this->errorHandler->get('lastError');
          $isHtml = $lastError['isHtml'];
          $backtrace = $lastError['backtrace'];
          $html = '<h3>Fatal Error</h3>';
          $html .= '<ul class="list-unstyled indent">';
          if (\count($backtrace) > 1) {
              // more than one trace frame
              $table = $this->outputHtml->buildTable(
                  $backtrace,
                  array(
                      'attribs' => 'trace table-bordered',
                      'caption' => 'trace',
                      'columns' => array('file','line','function'),
                  )
              );
              $html .= '<li>'.$lastError['message'].'</li>';
              $html .= '<li>'.$table.'</li>';
              if (!$isHtml) {
                  $html = \str_replace($lastError['message'], \htmlspecialchars($lastError['message']), $html);
              }
          } else {
              $keysKeep = array('typeStr','message','file','line');
              $lastError = \array_intersect_key($lastError, \array_flip($keysKeep));
              $html .= '<li>'.$this->outputHtml->dump($lastError).'</li>';
              if ($isHtml) {
                  $html = \str_replace(\htmlspecialchars($lastError['message']), $lastError['message'], $html);
              }
          }
          if (!\extension_loaded('xdebug')) {
              $html .= '<li>Want to see a backtrace here?  Install <a target="_blank" href="https://xdebug.org/docs/install">xdebug</a> PHP extension.</li>';
          }
          $html .= '</ul>';
          return $html;
      }
docs: If lastError was fatal, output the error
  
  @return string