code: private function getDefaultOutputAs()
      {
          $ret = 'html';
          $interface = $this->debug->utilities->getInterface();
          if ($interface == 'ajax') {
              $ret = $this->cfg['outputAsDefaultNonHtml'];
          } elseif ($interface == 'http') {
              $contentType = $this->debug->utilities->getResponseHeader();
              if ($contentType && $contentType !== 'text/html') {
                  $ret = $this->cfg['outputAsDefaultNonHtml'];
              }
          } else {
              $ret = 'text';
          }
          return $ret;
      }
docs: Determine default outputAs
  
  @return string