diff --git a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
index f98fb71..07dce6e 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
@@ -51,9 +51,10 @@ class MainContentViewSubscriber implements EventSubscriberInterface {
   /**
    * URL query attribute to indicate the wrapper used to render a request.
    *
-   * This controls wrapping the HTML content for example in a modal dialog.
+   * The wrapper format determines how the HTML is wrapped, for example in a
+   * modal dialog.
    */
-  const WRAPPER_ENVELOPE = '_wrapper_format';
+  const WRAPPER_FORMAT = '_wrapper_format';
 
   /**
    * Constructs a new MainContentViewSubscriber object.
@@ -82,8 +83,8 @@ public function onViewRenderArray(GetResponseForControllerResultEvent $event) {
     $result = $event->getControllerResult();
 
     // Render the controller result into a response if it's a render array.
-    if (is_array($result) && ($request->query->has(static::WRAPPER_ENVELOPE) || $request->getRequestFormat() == 'html')) {
-      $wrapper = $request->query->get(static::WRAPPER_ENVELOPE, 'html');
+    if (is_array($result) && ($request->query->has(static::WRAPPER_FORMAT) || $request->getRequestFormat() == 'html')) {
+      $wrapper = $request->query->get(static::WRAPPER_FORMAT, 'html');
 
       // Fall back to HTML if the requested wrapper envelope is not available.
       $wrapper = isset($this->mainContentRenderers[$wrapper]) ? $wrapper : 'html';
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index c1dd726..d80c2c5 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -271,7 +271,7 @@
     else {
       ajax.options.url += '&';
     }
-    ajax.options.url += Drupal.ajax.WRAPPER_ENVELOPE + '=drupal_' + (element_settings.dialogType || 'ajax');
+    ajax.options.url += Drupal.ajax.WRAPPER_FORMAT + '=drupal_' + (element_settings.dialogType || 'ajax');
 
     // Bind the ajaxSubmit function to the element event.
     $(ajax.element).on(element_settings.event, function (event) {
@@ -298,9 +298,10 @@
   /**
    * URL query attribute to indicate the wrapper used to render a request.
    *
-   * This controls wrapping the HTML content for example in a modal dialog.
+   * The wrapper format determines how the HTML is wrapped, for example in a
+   * modal dialog.
    */
-  Drupal.ajax.WRAPPER_ENVELOPE = '_wrapper_format';
+  Drupal.ajax.WRAPPER_FORMAT = '_wrapper_format';
 
   /**
    * Handle a key press.
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index e276832..99cb227 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -1423,8 +1423,8 @@ 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 $headers = array()) {
-    if (!isset($options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE])) {
-      $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE] = 'drupal_ajax';
+    if (!isset($options['query'][MainContentViewSubscriber::WRAPPER_FORMAT])) {
+      $options['query'][MainContentViewSubscriber::WRAPPER_FORMAT] = 'drupal_ajax';
     }
     return Json::decode($this->drupalGet($path, $options, $headers));
   }
@@ -1659,16 +1659,16 @@ protected function drupalPostAjaxForm($path, $edit, $triggering_element, $ajax_p
       // Avoid sending the wrapper query argument to drupalGet so we can fetch
       // the form and populate the internal WebTest values.
       $get_options = $options;
-      unset($get_options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE]);
+      unset($get_options['query'][MainContentViewSubscriber::WRAPPER_FORMAT]);
       $this->drupalGet($path, $get_options);
     }
     $content = $this->content;
     $drupal_settings = $this->drupalSettings;
 
     // Provide a default value for the wrapper envelope.
-    $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE] =
-      isset($options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE]) ?
-        $options['query'][MainContentViewSubscriber::WRAPPER_ENVELOPE] :
+    $options['query'][MainContentViewSubscriber::WRAPPER_FORMAT] =
+      isset($options['query'][MainContentViewSubscriber::WRAPPER_FORMAT]) ?
+        $options['query'][MainContentViewSubscriber::WRAPPER_FORMAT] :
         'drupal_ajax';
 
     // Get the Ajax settings bound to the triggering element.
diff --git a/core/modules/system/src/Tests/Ajax/DialogTest.php b/core/modules/system/src/Tests/Ajax/DialogTest.php
index 3783443..e290977 100644
--- a/core/modules/system/src/Tests/Ajax/DialogTest.php
+++ b/core/modules/system/src/Tests/Ajax/DialogTest.php
@@ -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('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_modal')));
+    $ajax_result = $this->drupalGetAjax('ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_FORMAT => '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('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_dialog')), array(), NULL, array(
+      ), array(), 'ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_FORMAT => '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('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_dialog')), array(), NULL, array(
+      ), array(), 'ajax-test/dialog-contents', array('query' => array(MainContentViewSubscriber::WRAPPER_FORMAT => 'drupal_dialog')), array(), NULL, array(
       // Don't send a target.
       'submit' => array()
     ));
@@ -160,7 +160,7 @@ 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('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_modal')));
+    $ajax_result = $this->drupalGetAjax('ajax-test/dialog-form', array('query' => array(MainContentViewSubscriber::WRAPPER_FORMAT => 'drupal_modal')));
     $expected_ajax_settings = [
       'edit-preview' => [
         'callback' => '::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('query' => array(MainContentViewSubscriber::WRAPPER_ENVELOPE => 'drupal_modal')));
+    $ajax_result = $this->drupalGetAjax('admin/structure/contact/add', array('query' => array(MainContentViewSubscriber::WRAPPER_FORMAT => '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']);