Elgg\Http\Request::isXmlHttpRequest PHP Method

    public function isXmlHttpRequest()
    {
        return strtolower($this->headers->get('X-Requested-With')) === 'xmlhttprequest' || $this->query->get('X-Requested-With') === 'XMLHttpRequest' || $this->request->get('X-Requested-With') === 'XMLHttpRequest';
        // GET/POST check is necessary for jQuery.form and other iframe-based "ajax". #8735
    }

 /**
  * Check if the request is an XmlHttpRequest
  * @return bool
  */
 public function isXhr()
 {
     return $this->request->isXmlHttpRequest();
 }