diff --git a/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
index 959c3565f2..91680d510b 100644
--- a/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -982,6 +982,9 @@
   /**
    * Provide a wrapper for new content via Ajax.
    *
+   * Wrap the inserted markup when trying to insert multiple root elements with
+   * a ajax effect.
+   *
    * @param {jQuery} $newContent
    *   Response elements after parsing.
    * @param {Drupal.Ajax} ajax
@@ -989,10 +992,10 @@
    * @param {object} response
    *   The response from the Ajax request.
    *
-   * @deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.0.
-   * Use data with desired wrapper.
+   * @deprecated in Drupal 8.6.x and will be removed before Drupal 9.0.0.
+   * Use data with desired wrapper. See https://www.drupal.org/node/2974880.
    *
-   * @todo: Add trigger an error after it will be possible. See
+   * @todo: Add deprecation warning after it will be possible. See
    * https://www.drupal.org/project/drupal/issues/2973400
    */
   Drupal.theme.ajaxWrapperNewContent = ($newContent, ajax, response) => (
@@ -1000,9 +1003,10 @@
     $newContent.filter(
       i =>
         !(
+          // We can not consider HTML comments or whitespace text as separate
+          // roots, since they do not cause visual regression with effect.
           $newContent[i].nodeName === '#comment' ||
-          ($newContent[i].nodeName === '#text' &&
-            /^(\s|\n|\r)*$/.test($newContent[i].textContent))
+          ($newContent[i].nodeName === '#text' && /^(\s|\n|\r)*$/.test($newContent[i].textContent))
         ),
     ).length > 1
       ? Drupal.theme('ajaxWrapperMultipleRootElements', $newContent)
@@ -1015,10 +1019,10 @@
    * @param {jQuery} $elements
    *   Response elements after parsing.
    *
-   * @deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.0.
-   * Use data with desired wrapper.
+   * @deprecated in Drupal 8.6.x and will be removed before Drupal 9.0.0.
+   * Use data with desired wrapper. See https://www.drupal.org/node/2974880.
    *
-   * @todo: Add trigger an error after it will be possible. See
+   * @todo: Add deprecation warning after it will be possible. See
    * https://www.drupal.org/project/drupal/issues/2973400
    */
   Drupal.theme.ajaxWrapperMultipleRootElements = ($elements) => (
@@ -1084,8 +1088,9 @@
 
       // Parse response.data into an element collection.
       let $newContent = $($.parseHTML(response.data, document, true));
-      // For backward compatibility, in some cases a wrapper will be added. Use
-      // theming to change it. See https://www.drupal.org/node/2940704.
+      // For backward compatibility, in some cases a wrapper will be added. This
+      // behavior will be removed before Drupal 9.0.0. Use theming to change it.
+      // See https://www.drupal.org/node/2940704.
       $newContent = Drupal.theme('ajaxWrapperNewContent', $newContent, ajax, response);
 
       // If removing content from the wrapper, detach behaviors first.
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 68c85ad3d9..1897719f61 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
@@ -43,7 +43,7 @@ public static function dialogContents() {
   }
 
   /**
-   * Example content for testing whether response should be wrapped in div.
+   * Example content for testing the wrapper of the response.
    *
    * @param string $type
    *   Type of response.
@@ -52,16 +52,13 @@ public static function dialogContents() {
    *   Renderable array of AJAX response contents.
    */
   public function renderTypes($type) {
-    $content = [
+    return [
       '#title' => '<em>AJAX Dialog & contents</em>',
       'content' => [
         '#type' => 'inline_template',
         '#template' => $this->getRenderTypes()[$type]['render'],
       ],
     ];
-
-    $content['effect'] = 'fade';
-    return $content;
   }
 
   /**