diff --git a/core/core.services.yml b/core/core.services.yml
index 3ff7f36..891d0b7 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -570,10 +570,6 @@ services:
   http_negotiation.format_negotiator:
     class: Drupal\Core\ContentNegotiation
     private: true
-  http_negotiation.wrapper_format_subscriber:
-    class: Drupal\Core\EventSubscriber\WrapperFormatSubscriber
-    tags:
-      - { name: event_subscriber }
   http_middleware.negotiation:
     class: Drupal\Core\StackMiddleware\NegotiationMiddleware
     arguments: ['@http_negotiation.format_negotiator']
diff --git a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
index fcc51a3..c9ad6f8 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
@@ -50,6 +50,8 @@ class MainContentViewSubscriber implements EventSubscriberInterface {
    */
   protected $mainContentRenderers;
 
+  const WRAPPER_ENVELOPE = '_wrapper_format';
+
   /**
    * Constructs a new MainContentViewSubscriber object.
    *
@@ -76,20 +78,17 @@ public function onViewRenderArray(GetResponseForControllerResultEvent $event) {
     $request = $event->getRequest();
     $result = $event->getControllerResult();
 
-    $format = $request->getRequestFormat();
-
     // Render the controller result into a response if it's a render array.
     if (is_array($result)) {
-      if (isset($this->mainContentRenderers[$format])) {
-        $renderer = $this->classResolver->getInstanceFromDefinition($this->mainContentRenderers[$format]);
+      $wrapper = $request->query->get(static::WRAPPER_ENVELOPE, 'html');
+      if (isset($this->mainContentRenderers[$wrapper])) {
+        $renderer = $this->classResolver->getInstanceFromDefinition($this->mainContentRenderers[$wrapper]);
         $event->setResponse($renderer->renderResponse($result, $request, $this->routeMatch));
       }
       else {
-        $supported_formats = array_keys($this->mainContentRenderers);
-        $supported_mimetypes = array_map([$request, 'getMimeType'], $supported_formats);
         $event->setResponse(new JsonResponse([
           'message' => 'Not Acceptable.',
-          'supported_mime_types' => $supported_mimetypes,
+          'supported_wrapper_envelopes' => array_keys($this->mainContentRenderers),
         ], 406));
       }
     }
diff --git a/core/lib/Drupal/Core/EventSubscriber/WrapperFormatSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/WrapperFormatSubscriber.php
deleted file mode 100644
index f293c57..0000000
--- a/core/lib/Drupal/Core/EventSubscriber/WrapperFormatSubscriber.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\EventSubscriber\WrapperFormatSubscriber.
- */
-
-namespace Drupal\Core\EventSubscriber;
-
-use Symfony\Component\EventDispatcher\EventSubscriberInterface;
-use Symfony\Component\HttpKernel\Event\GetResponseEvent;
-use Symfony\Component\HttpKernel\KernelEvents;
-
-/**
- * Sets the wrapper format, if specified for the request.
- */
-class WrapperFormatSubscriber implements EventSubscriberInterface {
-
-  const WRAPPER_FORMAT = '_wrapper_format';
-
-  /**
-   * Sets the wrapper format, if specified for the request.
-   */
-  public function onRequest(GetResponseEvent $event) {
-    $request = $event->getRequest();
-    if ($request->query->has(static::WRAPPER_FORMAT)) {
-      $request->setRequestFormat($request->query->get(static::WRAPPER_FORMAT));
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public static function getSubscribedEvents() {
-    $events[KernelEvents::REQUEST][] = ['onRequest', 48];
-
-    return $events;
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Render/Element/RenderElement.php b/core/lib/Drupal/Core/Render/Element/RenderElement.php
index 7600f62..b9de164 100644
--- a/core/lib/Drupal/Core/Render/Element/RenderElement.php
+++ b/core/lib/Drupal/Core/Render/Element/RenderElement.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Core\Render\Element;
 
-use Drupal\Core\EventSubscriber\WrapperFormatSubscriber;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\PluginBase;
 use Drupal\Core\Render\Element;
@@ -241,7 +241,7 @@ public static function preRenderAjaxForm($element) {
       $settings += array(
         'url' => isset($settings['callback']) ? Url::fromRoute('system.ajax') : NULL,
         'options' => array(),
-        WrapperFormatSubscriber::WRAPPER_FORMAT => 'ajax',
+        MainContentViewSubscriber::WRAPPER_ENVELOPE => 'ajax',
       );
 
       // @todo Legacy support. Remove in Drupal 8.
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index fe96f9f..5b8b109 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -20,6 +20,7 @@
 use Drupal\Core\Database\Database;
 use Drupal\Core\Database\ConnectionNotDefinedException;
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Session\AccountInterface;
@@ -1556,8 +1557,8 @@ protected function drupalGetJSON($path, array $options = array(), array $headers
    * Requests a Drupal path in drupal_ajax format and JSON-decodes the response.
    */
   protected function drupalGetAjax($path, array $options = array(), array $headers = array()) {
-    if (!preg_grep('/^Accept:/', $headers)) {
-      $headers[] = 'Accept: application/vnd.drupal-ajax';
+    if (!isset($options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE])) {
+      $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE] = 'drupal_ajax';
     }
     return Json::decode($this->drupalGet($path, $options, $headers));
   }
@@ -1785,6 +1786,11 @@ protected function drupalPostForm($path, $edit, $submit, array $options = array(
    * @see ajax.js
    */
   protected function drupalPostAjaxForm($path, $edit, $triggering_element, $ajax_path = NULL, array $options = array(), array $headers = array(), $form_html_id = NULL, $ajax_settings = NULL) {
+    if (isset($options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE])) {
+      $original_wrapper = $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE];
+      unset($options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE]);
+    }
+
     // Get the content of the initial page prior to calling drupalPostForm(),
     // since drupalPostForm() replaces $this->content.
     if (isset($path)) {
@@ -1793,8 +1799,11 @@ protected function drupalPostAjaxForm($path, $edit, $triggering_element, $ajax_p
     $content = $this->content;
     $drupal_settings = $this->drupalSettings;
 
-    if (!preg_grep('/^Accept:/', $headers)) {
-      $headers[] = 'Accept: application/vnd.drupal-ajax';
+    if (isset($original_wrapper)) {
+      $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE] = $original_wrapper;
+    }
+    else {
+      $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE] = 'drupal_ajax';
     }
 
     // Get the Ajax settings bound to the triggering element.
@@ -1834,8 +1843,9 @@ protected function drupalPostAjaxForm($path, $edit, $triggering_element, $ajax_p
     // Unless a particular path is specified, use the one specified by the
     // Ajax settings, or else 'system/ajax'.
     if (!isset($ajax_path)) {
-      $ajax_path = isset($ajax_settings['url']) ? $ajax_settings['url'] : 'system/ajax';
+      $ajax_path = isset($ajax_settings['url']) ? preg_replace('/^' . preg_quote($GLOBALS['base_path'], '/') . '/', '', $ajax_settings['url']) : 'system/ajax';
     }
+    $ajax_path = $this->container->get('url_generator')->generateFromPath($ajax_path, $options);
 
     // Submit the POST request.
     $return = Json::decode($this->drupalPostForm(NULL, $edit, array('path' => $ajax_path, 'triggering_element' => $triggering_element), $options, $headers, $form_html_id, $extra_post));
diff --git a/core/modules/system/src/Tests/Ajax/DialogTest.php b/core/modules/system/src/Tests/Ajax/DialogTest.php
index 741ee5d..c78e94c 100644
--- a/core/modules/system/src/Tests/Ajax/DialogTest.php
+++ b/core/modules/system/src/Tests/Ajax/DialogTest.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\system\Tests\Ajax;
 
-use Drupal\Core\EventSubscriber\WrapperFormatSubscriber;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Url;
 
 /**
@@ -94,7 +94,7 @@ public function testDialog() {
     $this->assertRaw($dialog_contents, 'Non-JS modal dialog page present.');
 
     // Emulate going to the JS version of the page and check the JSON response.
-    $ajax_result = $this->drupalGetAjax('ajax-test/dialog-contents', array(), array('Accept: application/vnd.drupal-modal'));
+    $ajax_result = $this->drupalGetAjax('ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_modal')));
     $this->assertEqual($modal_expected_response, $ajax_result[3], 'Modal dialog JSON response matches.');
 
     // Check that requesting a "normal" dialog without JS goes to a page.
@@ -107,7 +107,7 @@ public function testDialog() {
     $ajax_result = $this->drupalPostAjaxForm('ajax-test/dialog', array(
         // We have to mock a form element to make drupalPost submit from a link.
         'textfield' => 'test',
-      ), array(), 'ajax-test/dialog-contents', array(), array('Accept: application/vnd.drupal-dialog'), NULL, array(
+      ), array(), 'ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_dialog')), array(), NULL, array(
       'submit' => array(
         'dialogOptions[target]' => 'ajax-test-dialog-wrapper-1',
       )
@@ -120,7 +120,7 @@ public function testDialog() {
     $ajax_result = $this->drupalPostAjaxForm('ajax-test/dialog', array(
         // We have to mock a form element to make drupalPost submit from a link.
         'textfield' => 'test',
-      ), array(), 'ajax-test/dialog-contents', array(), array('Accept: application/vnd.drupal-dialog'), NULL, array(
+      ), array(), 'ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_dialog')), array(), NULL, array(
       // Don't send a target.
       'submit' => array()
     ));
@@ -160,13 +160,13 @@ public function testDialog() {
     $this->assertTrue(!empty($form), 'Non-JS form page present.');
 
     // Emulate going to the JS version of the form and check the JSON response.
-    $ajax_result = $this->drupalGetAjax('ajax-test/dialog-form', array(), array('Accept: application/vnd.drupal-modal'));
+    $ajax_result = $this->drupalGetAjax('ajax-test/dialog-form', array('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_modal')));
     $expected_ajax_settings = [
       'edit-preview' => [
         'callback' => '::preview',
         'event' => 'click',
         'url' => Url::fromRoute('system.ajax')->toString(),
-        WrapperFormatSubscriber::WRAPPER_FORMAT => 'ajax',
+        MainContentViewSubscriber::WRAPPER_ENVELOPE => 'ajax',
         'submit' => [
           '_triggering_element_name' => 'op',
           '_triggering_element_value' => 'Preview',
@@ -189,7 +189,7 @@ public function testDialog() {
     $this->assertTrue(!empty($form), 'Non-JS entity form page present.');
 
     // Emulate going to the JS version of the form and check the JSON response.
-    $ajax_result = $this->drupalGetAjax('admin/structure/contact/add', array(), array('Accept: application/vnd.drupal-modal'));
+    $ajax_result = $this->drupalGetAjax('admin/structure/contact/add', array('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_modal')));
     $this->setRawContent($ajax_result[3]['data']);
     // Remove the data, the form build id and token will never match.
     unset($ajax_result[3]['data']);
diff --git a/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php b/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
index ba261cb..663a904 100644
--- a/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
+++ b/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
@@ -120,7 +120,7 @@ public function dialog() {
       '#url' => Url::fromRoute('ajax_test.dialog_contents'),
       '#attributes' => array(
         'class' => array('use-ajax'),
-        'data-accepts' => 'application/vnd.drupal-modal',
+        'data-accepts' => 'application/vnd.drupal-modal', // TODO replace this.
       ),
     );