diff --git a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
index 0dd8e2f..cbdce65 100644
--- a/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php
@@ -50,6 +50,11 @@ class MainContentViewSubscriber implements EventSubscriberInterface {
    */
   protected $mainContentRenderers;
 
+  /**
+   * Url query attribute to indicate the wrapper used to render a request.
+   *
+   * This controls wrapping the HTML content for example in a modal dialog.
+   */
   const WRAPPER_ENVELOPE = '_wrapper_format';
 
   /**
@@ -80,7 +85,7 @@ public function onViewRenderArray(GetResponseForControllerResultEvent $event) {
 
     // Render the controller result into a response if it's a render array.
     if (is_array($result)) {
-      // We default to requestFormat() because content negotiation uses this as
+      // We default to getRequestFormat() because content negotiation uses this as
       // its fallback method for displaying a 406 when we fail to match a route
       // based on format.
       // @todo this logic should be replaced with a more clear opt in to avoid
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index 0ccd579..1e26c9d 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -17,6 +17,13 @@
   Drupal.ajax = Drupal.ajax || {};
 
   /**
+   * Url query attribute to indicate the wrapper used to render a request.
+   *
+   * This controls wrapping the HTML content for example in a modal dialog.
+   */
+  Drupal.ajax.WRAPPER_ENVELOPE = '_wrapper_format';
+
+  /**
    * Attaches the Ajax behavior to each Ajax form element.
    */
   Drupal.behaviors.AJAX = {
@@ -272,7 +279,7 @@
       else {
         ajax.options.url += '&';
       }
-      ajax.options.url += '_wrapper_format=drupal_' + element_settings.dialogType;
+      ajax.options.url += Drupal.ajax.WRAPPER_ENVELOPE + '=drupal_' + element_settings.dialogType;
     }
 
     // Bind the ajaxSubmit function to the element event.
diff --git a/core/modules/ckeditor/js/ckeditor.js b/core/modules/ckeditor/js/ckeditor.js
index 7f9dbf0..525f8d2 100644
--- a/core/modules/ckeditor/js/ckeditor.js
+++ b/core/modules/ckeditor/js/ckeditor.js
@@ -160,8 +160,8 @@
       // a Drupal.ajax instance to load the dialog and trigger it.
       var $content = $('<div class="ckeditor-dialog-loading"><span style="top: -40px;" class="ckeditor-dialog-loading-link"><a>' + Drupal.t('Loading...') + '</a></span></div>');
       $content.appendTo($target);
-      new Drupal.ajax('ckeditor-dialog', $content.find('a').get(0), {
-        _wrapper_format: 'modal',
+
+      var options = {
         dialog: dialogSettings,
         selector: '.ckeditor-dialog-loading-link',
         url: url,
@@ -170,7 +170,9 @@
         submit: {
           editor_object: existingValues
         }
-      });
+      };
+      options[Drupal.ajax.WRAPPER_ENVELOPE] = 'modal';
+      new Drupal.ajax('ckeditor-dialog', $content.find('a').get(0), options);
       $content.find('a')
         .on('click', function () { return false; })
         .trigger('ckeditor-internal.ckeditor');