Symfony\Component\HttpFoundation\Request::isXmlHttpRequest PHP Method

    public function isXmlHttpRequest()
    {
        return 'XMLHttpRequest' == $this->headers->get('X-Requested-With');
    }

 /**
  * @Route("/{applicationId}")
  * @Method({"GET", "POST"})
  * @Template()
  * @param Request $request
  * @param $applicationId
  * @return array
  */
 public function indexAction(Request $request, $applicationId)
 {
     // Validate the $applicationId, throws Exception if invalid.
     $application = $this->getApplication($this->irisEntityManager, $applicationId);
     // Get the Case for this Tenant and put in the session, as it's needed throughout
     $case = $this->getCase($this->irisEntityManager, $application->getCaseId());
     $request->getSession()->set('submitted-case', serialize($case));
     // Create an empty ReferencingGuarantor object.
     $guarantor = new ReferencingGuarantor();
     $guarantor->setCaseId($application->getCaseId());
     // Build the form.
     $form = $this->createForm($this->formType, $guarantor, array('guarantor_decorator' => $this->referencingGuarantorDecoratorBridgeSubscriber->getGuarantorDecorator(), 'attr' => array('id' => 'generic_step_form', 'class' => 'referencing branded individual-guarantor-form', 'novalidate' => 'novalidate')));
     // Process a client round trip, if necessary
     if ($request->isXmlHttpRequest()) {
         $form->submit($request);
         return $this->render('BarbonHostedApiLandlordReferenceBundle:NewReference/Guarantor/Validate:index.html.twig', array('form' => $form->createView()));
     }
     // Submit the form.
     $form->handleRequest($request);
     if ($form->isValid()) {
         $case = $this->getCase($this->irisEntityManager, $application->getCaseId());
         // Dispatch the new guarantor reference event.
         $this->eventDispatcher->dispatch(NewReferenceEvents::GUARANTOR_REFERENCE_CREATED, new NewGuarantorReferenceEvent($case, $application, $guarantor));
         // Send the user to the success page.
         return $this->redirectToRoute('barbon_hostedapi_landlord_reference_newreference_guarantor_confirmation_index', array('applicationId' => $applicationId));
     }
     return array('form' => $form->createView());
 }