diff --git a/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
index 6248e46..e96f3ae 100644
--- a/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -1009,38 +1009,73 @@ else if (type === 'fade') {
      *   A optional jQuery selector string.
      * @param {object} [response.settings]
      *   An optional array of settings that will be used.
-     * @param {number} [status]
-     *   The XMLHttpRequest status.
      */
-    insert(ajax, response, status) {
+    insert(ajax, response) {
       // Get information from the response. If it is not there, default to
       // our presets.
       const $wrapper = response.selector ? $(response.selector) : $(ajax.wrapper);
       const method = response.method || ajax.method;
       const effect = ajax.getEffect(response);
-      let settings;
+
+      // Apply any settings from the returned JSON if available.
+      const settings = response.settings || ajax.settings || drupalSettings;
 
       // We don't know what response.data contains: it might be a string of text
       // without HTML, so don't rely on jQuery correctly interpreting
       // $(response.data) as new HTML rather than a CSS selector. Also, if
       // response.data contains top-level text nodes, they get lost with either
       // $(response.data) or $('<div></div>').replaceWith(response.data).
-      const $new_content_wrapped = $('<div></div>').html(response.data);
-      let $new_content = $new_content_wrapped.contents();
+      // attachBehaviors() can, for the same reason, not be called with a
+      // context object that includes top-level text nodes. Therefore text nodes
+      // will be wrapped with a <span> element. This also gives themers the
+      // possibility to style the response.
+      let $newContent;
+      // We use the trimmed data to be able to detect cases when the response
+      // has only top-level elements or comment nodes with extra whitespace
+      // around. In that case whitespaces are removed and the response
+      // should not be wrapped.
+      // For example:
+      //   '  <div>content</div> ' is equivalent to '<div>content</div>' and
+      // no extra wrapper will be added.
+      const trimmedData = response.data.trim();
+      // List of DOM nodes contained in the response for processing.
+      let responseDataNodes;
 
-      // For legacy reasons, the effects processing code assumes that
-      // $new_content consists of a single top-level element. Also, it has not
-      // been sufficiently tested whether attachBehaviors() can be successfully
-      // called with a context object that includes top-level text nodes.
-      // However, to give developers full control of the HTML appearing in the
-      // page, and to enable Ajax content to be inserted in places where <div>
-      // elements are not allowed (e.g., within <table>, <tr>, and <span>
-      // parents), we check if the new content satisfies the requirement
-      // of a single top-level element, and only use the container <div> created
-      // above when it doesn't. For more information, please see
-      // https://www.drupal.org/node/736066.
-      if ($new_content.length !== 1 || $new_content.get(0).nodeType !== 1) {
-        $new_content = $new_content_wrapped;
+      // When 'data' is empty or is only whitespace, manually create the node
+      // array because parseHTML would return null.
+      if (trimmedData === '') {
+        responseDataNodes = [document.createTextNode(response.data)];
+      }
+      else {
+        responseDataNodes = $.parseHTML(trimmedData, true);
+      }
+      // Check every node for it's type to decide if wrapping is necessary.
+      const onlyElementNodes = responseDataNodes.every(
+        element => element.nodeType === Node.ELEMENT_NODE || element.nodeType === Node.COMMENT_NODE,
+      );
+
+      // When there are only element and/or comment nodes in the response, no
+      // extra wrapping necessary.
+      if (onlyElementNodes) {
+        $newContent = $(trimmedData);
+      }
+      // When there are other types of top-level nodes, the response needs to be
+      // wrapped.
+      else {
+        const onlyTextOrCommentNodes = responseDataNodes.every(
+          element => element.nodeType === Node.COMMENT_NODE || element.nodeType === Node.TEXT_NODE,
+        );
+        // If response.data contains only nodes of the type TEXT_NODE or
+        // COMMENT_NODE, or the wrapping element is not styled as a block,
+        // response.data will be wrapped with SPAN.
+        if (onlyTextOrCommentNodes || $wrapper.css('display') !== 'block') {
+          $newContent = $('<span></span>');
+        }
+        else {
+          $newContent = $('<div></div>');
+        }
+        // Use response.data to keep whitespace as-is.
+        $newContent.html(response.data);
       }
 
       // If removing content from the wrapper, detach behaviors first.
@@ -1050,36 +1085,42 @@ else if (type === 'fade') {
         case 'replaceAll':
         case 'empty':
         case 'remove':
-          settings = response.settings || ajax.settings || drupalSettings;
           Drupal.detachBehaviors($wrapper.get(0), settings);
+          break;
+        default:
+          break;
       }
 
       // Add the new content to the page.
-      $wrapper[method]($new_content);
+      $wrapper[method]($newContent);
 
       // Immediately hide the new content if we're using any effects.
       if (effect.showEffect !== 'show') {
-        $new_content.hide();
+        $newContent.hide();
       }
 
       // Determine which effect to use and what content will receive the
       // effect, then show the new content.
-      if ($new_content.find('.ajax-new-content').length > 0) {
-        $new_content.find('.ajax-new-content').hide();
-        $new_content.show();
-        $new_content.find('.ajax-new-content')[effect.showEffect](effect.showSpeed);
+      const $ajaxNewContent = $newContent.find('.ajax-new-content');
+      if ($ajaxNewContent.length) {
+        $ajaxNewContent.hide();
+        $newContent.show();
+        $ajaxNewContent[effect.showEffect](effect.showSpeed);
       }
       else if (effect.showEffect !== 'show') {
-        $new_content[effect.showEffect](effect.showSpeed);
+        $newContent[effect.showEffect](effect.showSpeed);
       }
 
       // Attach all JavaScript behaviors to the new content, if it was
       // successfully added to the page, this if statement allows
       // `#ajax['wrapper']` to be optional.
-      if ($new_content.parents('html').length > 0) {
-        // Apply any settings from the returned JSON if available.
-        settings = response.settings || ajax.settings || drupalSettings;
-        Drupal.attachBehaviors($new_content.get(0), settings);
+      if ($newContent.parents('html').length) {
+        // Attach behaviors to all element nodes.
+        $newContent.each((index, element) => {
+          if (element.nodeType === Node.ELEMENT_NODE) {
+            Drupal.attachBehaviors(element, settings);
+          }
+        });
       }
     },
 
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index 5ea5242..c669d8f 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -474,46 +474,78 @@ function loadAjaxBehavior(base) {
 
   Drupal.AjaxCommands = function () {};
   Drupal.AjaxCommands.prototype = {
-    insert: function insert(ajax, response, status) {
+    insert: function insert(ajax, response) {
       var $wrapper = response.selector ? $(response.selector) : $(ajax.wrapper);
       var method = response.method || ajax.method;
       var effect = ajax.getEffect(response);
-      var settings = void 0;
 
-      var $new_content_wrapped = $('<div></div>').html(response.data);
-      var $new_content = $new_content_wrapped.contents();
+      var settings = response.settings || ajax.settings || drupalSettings;
 
-      if ($new_content.length !== 1 || $new_content.get(0).nodeType !== 1) {
-        $new_content = $new_content_wrapped;
+      var $newContent = void 0;
+
+      var trimmedData = response.data.trim();
+
+      var responseDataNodes = void 0;
+
+      if (trimmedData === '') {
+        responseDataNodes = [document.createTextNode(response.data)];
+      } else {
+        responseDataNodes = $.parseHTML(trimmedData, true);
       }
 
+      var onlyElementNodes = responseDataNodes.every(function (element) {
+        return element.nodeType === Node.ELEMENT_NODE || element.nodeType === Node.COMMENT_NODE;
+      });
+
+      if (onlyElementNodes) {
+        $newContent = $(trimmedData);
+      } else {
+          var onlyTextOrCommentNodes = responseDataNodes.every(function (element) {
+            return element.nodeType === Node.COMMENT_NODE || element.nodeType === Node.TEXT_NODE;
+          });
+
+          if (onlyTextOrCommentNodes || $wrapper.css('display') !== 'block') {
+            $newContent = $('<span></span>');
+          } else {
+            $newContent = $('<div></div>');
+          }
+
+          $newContent.html(response.data);
+        }
+
       switch (method) {
         case 'html':
         case 'replaceWith':
         case 'replaceAll':
         case 'empty':
         case 'remove':
-          settings = response.settings || ajax.settings || drupalSettings;
           Drupal.detachBehaviors($wrapper.get(0), settings);
+          break;
+        default:
+          break;
       }
 
-      $wrapper[method]($new_content);
+      $wrapper[method]($newContent);
 
       if (effect.showEffect !== 'show') {
-        $new_content.hide();
+        $newContent.hide();
       }
 
-      if ($new_content.find('.ajax-new-content').length > 0) {
-        $new_content.find('.ajax-new-content').hide();
-        $new_content.show();
-        $new_content.find('.ajax-new-content')[effect.showEffect](effect.showSpeed);
+      var $ajaxNewContent = $newContent.find('.ajax-new-content');
+      if ($ajaxNewContent.length) {
+        $ajaxNewContent.hide();
+        $newContent.show();
+        $ajaxNewContent[effect.showEffect](effect.showSpeed);
       } else if (effect.showEffect !== 'show') {
-        $new_content[effect.showEffect](effect.showSpeed);
+        $newContent[effect.showEffect](effect.showSpeed);
       }
 
-      if ($new_content.parents('html').length > 0) {
-        settings = response.settings || ajax.settings || drupalSettings;
-        Drupal.attachBehaviors($new_content.get(0), settings);
+      if ($newContent.parents('html').length) {
+        $newContent.each(function (index, element) {
+          if (element.nodeType === Node.ELEMENT_NODE) {
+            Drupal.attachBehaviors(element, settings);
+          }
+        });
       }
     },
     remove: function remove(ajax, response, status) {
diff --git a/core/modules/system/tests/modules/ajax_test/ajax_test.libraries.yml b/core/modules/system/tests/modules/ajax_test/ajax_test.libraries.yml
index f1c7306..772a05f 100644
--- a/core/modules/system/tests/modules/ajax_test/ajax_test.libraries.yml
+++ b/core/modules/system/tests/modules/ajax_test/ajax_test.libraries.yml
@@ -1,3 +1,8 @@
+ajax_insert:
+  js:
+    js/insert-ajax.js: {}
+  dependencies:
+    - core/drupal.ajax
 order:
  drupalSettings:
    ajax: test
diff --git a/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml b/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml
index e8d06c0..89191a1 100644
--- a/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml
+++ b/core/modules/system/tests/modules/ajax_test/ajax_test.routing.yml
@@ -6,6 +6,14 @@ ajax_test.dialog_contents:
   requirements:
     _access: 'TRUE'
 
+ajax_test.ajax_render_types:
+  path: '/ajax-test/dialog-contents-types/{type}'
+  defaults:
+    _title: 'AJAX Dialog contents routing'
+    _controller: '\Drupal\ajax_test\Controller\AjaxTestController::renderTypes'
+  requirements:
+    _access: 'TRUE'
+
 ajax_test.dialog_form:
   path: '/ajax-test/dialog-form'
   defaults:
@@ -21,6 +29,13 @@ ajax_test.dialog:
   requirements:
     _access: 'TRUE'
 
+ajax_test.insert_links:
+  path: '/ajax-test/insert'
+  defaults:
+    _controller: '\Drupal\ajax_test\Controller\AjaxTestController::insertLinks'
+  requirements:
+    _access: 'TRUE'
+
 ajax_test.dialog_close:
   path: '/ajax-test/dialog-close'
   defaults:
diff --git a/core/modules/system/tests/modules/ajax_test/js/insert-ajax.es6.js b/core/modules/system/tests/modules/ajax_test/js/insert-ajax.es6.js
new file mode 100644
index 0000000..e7fb3f2
--- /dev/null
+++ b/core/modules/system/tests/modules/ajax_test/js/insert-ajax.es6.js
@@ -0,0 +1,39 @@
+/**
+ * @file
+ * Drupal behavior to attach click event handlers to ajax-insert and
+ * ajax-insert-inline links for testing ajax requests.
+ */
+
+(function ($, window, Drupal) {
+  Drupal.behaviors.insertTest = {
+    attach(context) {
+      $('.ajax-insert').once('ajax-insert').on('click', (event) => {
+        event.preventDefault();
+        const ajaxSettings = {
+          url: event.currentTarget.getAttribute('href'),
+          wrapper: 'ajax-target',
+          base: false,
+          element: false,
+          method: event.currentTarget.getAttribute('data-method'),
+        };
+        const myAjaxObject = Drupal.ajax(ajaxSettings);
+        myAjaxObject.execute();
+      });
+
+      $('.ajax-insert-inline').once('ajax-insert').on('click', (event) => {
+        event.preventDefault();
+        const ajaxSettings = {
+          url: event.currentTarget.getAttribute('href'),
+          wrapper: 'ajax-target-inline',
+          base: false,
+          element: false,
+          method: event.currentTarget.getAttribute('data-method'),
+        };
+        const myAjaxObject = Drupal.ajax(ajaxSettings);
+        myAjaxObject.execute();
+      });
+
+      $(context).addClass('processed');
+    },
+  };
+}(jQuery, window, Drupal));
diff --git a/core/modules/system/tests/modules/ajax_test/js/insert-ajax.js b/core/modules/system/tests/modules/ajax_test/js/insert-ajax.js
new file mode 100644
index 0000000..c261bca
--- /dev/null
+++ b/core/modules/system/tests/modules/ajax_test/js/insert-ajax.js
@@ -0,0 +1,40 @@
+/**
+* DO NOT EDIT THIS FILE.
+* See the following change record for more information,
+* https://www.drupal.org/node/2815083
+* @preserve
+**/
+
+(function ($, window, Drupal) {
+  Drupal.behaviors.insertTest = {
+    attach: function attach(context) {
+      $('.ajax-insert').once('ajax-insert').on('click', function (event) {
+        event.preventDefault();
+        var ajaxSettings = {
+          url: event.currentTarget.getAttribute('href'),
+          wrapper: 'ajax-target',
+          base: false,
+          element: false,
+          method: event.currentTarget.getAttribute('data-method')
+        };
+        var myAjaxObject = Drupal.ajax(ajaxSettings);
+        myAjaxObject.execute();
+      });
+
+      $('.ajax-insert-inline').once('ajax-insert').on('click', function (event) {
+        event.preventDefault();
+        var ajaxSettings = {
+          url: event.currentTarget.getAttribute('href'),
+          wrapper: 'ajax-target-inline',
+          base: false,
+          element: false,
+          method: event.currentTarget.getAttribute('data-method')
+        };
+        var myAjaxObject = Drupal.ajax(ajaxSettings);
+        myAjaxObject.execute();
+      });
+
+      $(context).addClass('processed');
+    }
+  };
+})(jQuery, window, Drupal);
\ No newline at end of file
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 5ba65e8..fcffcd1 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
@@ -43,6 +43,61 @@ public static function dialogContents() {
   }
 
   /**
+   * Example content for testing whether response should be wrapped in div.
+   *
+   * @param string $type
+   *   Type of response.
+   *
+   * @return array
+   *   Renderable array of AJAX response contents.
+   */
+  public function renderTypes($type) {
+    $content = [
+      '#title' => '<em>AJAX Dialog & contents</em>',
+      'content' => [
+        '#type' => 'inline_template',
+        '#template' => $this->getRenderTypes()[$type],
+      ],
+    ];
+
+    return $content;
+  }
+
+  /**
+   * Returns a render array of links that directly Drupal.ajax().
+   */
+  public function insertLinks() {
+    $methods = [
+      'html',
+      'replaceWith',
+    ];
+
+    $build['links'] = [
+      'ajax_target' => [
+        '#markup' => '<div id="ajax-target" data-drupal-ajax-target="">Target</div><span id="ajax-target-inline" data-drupal-ajax-target="">Target inline</span>',
+      ],
+      'links' => [
+        '#theme' => 'links',
+        '#attached' => ['library' => ['ajax_test/ajax_insert']],
+      ],
+    ];
+    foreach ($methods as $method) {
+      foreach (array_keys($this->getRenderTypes()) as $type) {
+        $class = $type == 'inline' ? 'ajax-insert-inline' : 'ajax-insert';
+        $build['links']['links']['#links']["$method-$type"] = [
+          'title' => "Link $method $type",
+          'url' => Url::fromRoute('ajax_test.ajax_render_types', ['type' => $type]),
+          'attributes' => [
+            'class' => [$class],
+            'data-method' => $method,
+          ],
+        ];
+      }
+    }
+    return $build;
+  }
+
+  /**
    * Returns a render array that will be rendered by AjaxRenderer.
    *
    * Verifies that the response incorporates JavaScript settings generated
@@ -222,4 +277,27 @@ public function dialogClose() {
     return $response;
   }
 
+  /**
+   * Render types.
+   *
+   * @return array
+   *   Render types.
+   */
+  protected function getRenderTypes() {
+    return [
+      'pre-wrapped' => '<div class="pre-wrapped">pre-wrapped<script> var test;</script></div>',
+      'pre-wrapped-whitespace' => ' <div class="pre-wrapped-whitespace">pre-wrapped-whitespace</div>' . "\r\n",
+      'not-wrapped' => 'not-wrapped',
+      'comment-string-not-wrapped' => '<!-- COMMENT -->comment-string-not-wrapped',
+      'comment-not-wrapped' => '<!-- COMMENT --><div class="comment-not-wrapped">comment-not-wrapped</div>',
+      'mixed' => ' foo <!-- COMMENT -->  foo bar<div class="a class"><p>some string</p></div> additional not wrapped strings, <!-- ANOTHER COMMENT --> <p>final string</p>',
+      'top-level-only' => '<div>element #1</div><div>element #2</div>',
+      'top-level-only-pre-whitespace' => ' <div>element #1</div><div>element #2</div> ',
+      'top-level-only-middle-whitespace' => '<div>element #1</div> <div>element #2</div>',
+      'inline' => 'inline <div>BLOCK LEVEL<script> var test;</script></div>',
+      'empty' => '',
+    ];
+  }
+
 }
+
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php
index 3d174b0..afa8420 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxFormPageCacheTest.php
@@ -55,8 +55,8 @@ public function testSimpleAJAXFormValue() {
 
     // Wait for the DOM to update. The HtmlCommand will update
     // #ajax_selected_color to reflect the color change.
-    $green_div = $this->assertSession()->waitForElement('css', "#ajax_selected_color div:contains('green')");
-    $this->assertNotNull($green_div, 'DOM update: The selected color DIV is green.');
+    $green_span = $this->assertSession()->waitForElement('css', "#ajax_selected_color span:contains('green')");
+    $this->assertNotNull($green_span, 'DOM update: The selected color SPAN is green.');
 
     // Confirm the operation of the UpdateBuildIdCommand.
     $build_id_first_ajax = $this->getFormBuildId();
@@ -67,8 +67,8 @@ public function testSimpleAJAXFormValue() {
     $session->getPage()->selectFieldOption('select', 'red');
 
     // Wait for the DOM to update.
-    $red_div = $this->assertSession()->waitForElement('css', "#ajax_selected_color div:contains('red')");
-    $this->assertNotNull($red_div, 'DOM update: The selected color DIV is red.');
+    $red_span = $this->assertSession()->waitForElement('css', "#ajax_selected_color span:contains('red')");
+    $this->assertNotNull($red_span, 'DOM update: The selected color SPAN is red.');
 
     // Confirm the operation of the UpdateBuildIdCommand.
     $build_id_second_ajax = $this->getFormBuildId();
@@ -86,8 +86,8 @@ public function testSimpleAJAXFormValue() {
     $session->getPage()->selectFieldOption('select', 'green');
 
     // Wait for the DOM to update.
-    $green_div2 = $this->assertSession()->waitForElement('css', "#ajax_selected_color div:contains('green')");
-    $this->assertNotNull($green_div2, 'DOM update: After reload - the selected color DIV is green.');
+    $green_span2 = $this->assertSession()->waitForElement('css', "#ajax_selected_color span:contains('green')");
+    $this->assertNotNull($green_span2, 'DOM update: After reload - the selected color SPAN is green.');
 
     $build_id_from_cache_first_ajax = $this->getFormBuildId();
     $this->assertNotEquals($build_id_from_cache_initial, $build_id_from_cache_first_ajax, 'Build id is changed in the simpletest-DOM on first AJAX submission');
@@ -98,8 +98,8 @@ public function testSimpleAJAXFormValue() {
     $session->getPage()->selectFieldOption('select', 'red');
 
     // Wait for the DOM to update.
-    $red_div2 = $this->assertSession()->waitForElement('css', "#ajax_selected_color div:contains('red')");
-    $this->assertNotNull($red_div2, 'DOM update: After reload - the selected color DIV is red.');
+    $red_span2 = $this->assertSession()->waitForElement('css', "#ajax_selected_color span:contains('red')");
+    $this->assertNotNull($red_span2, 'DOM update: After reload - the selected color SPAN is red.');
 
     $build_id_from_cache_second_ajax = $this->getFormBuildId();
     $this->assertNotEquals($build_id_from_cache_first_ajax, $build_id_from_cache_second_ajax, 'Build id changes on subsequent AJAX submissions');
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
index e059405..3633b65 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php
@@ -16,6 +16,25 @@ class AjaxTest extends JavascriptTestBase {
    */
   public static $modules = ['ajax_test'];
 
+  /**
+   * Wraps HTML with an AJAX target element.
+   *
+   * This reproduces recognizable parts of the wrapping markup from
+   * \Drupal\ajax_test\Controller\AjaxTestController::insertLinks and is not
+   * supposed to return valid HTML.
+   *
+   * @param string $html
+   *   The HTML to wrap.
+   *
+   * @return string
+   *   The HTML wrapped in the an AJAX target element.
+   *
+   * @see \Drupal\ajax_test\Controller\AjaxTestController::insertLinks
+   */
+  protected function wrapAjaxTarget($html) {
+    return 'data-drupal-ajax-target="">' . $html . '</';
+  }
+
   public function testAjaxWithAdminRoute() {
     \Drupal::service('theme_installer')->install(['stable', 'seven']);
     $theme_config = \Drupal::configFactory()->getEditable('system.theme');
@@ -82,4 +101,105 @@ public function testDrupalSettingsCachingRegression() {
     $this->assertNotContains($fake_library, $libraries);
   }
 
+  /**
+   * Tests that various AJAX responses with DOM elements are correctly inserted.
+   *
+   * After inserting DOM elements, Drupal JavaScript behaviors should be
+   * reattached and all top-level elements of type Node.ELEMENT_NODE need to be
+   * part of the context.
+   *
+   * @dataProvider providerTestInsert
+   */
+  public function testInsert($render_type, $expected) {
+    $assert = $this->assertSession();
+
+    $this->drupalGet('ajax-test/insert');
+    $this->clickLink("Link html $render_type");
+    $assert->assertWaitOnAjaxRequest();
+    // Extra span added by a second prepend command on the ajax requests.
+    $assert->responseContains($this->wrapAjaxTarget($expected));
+
+    $this->drupalGet('ajax-test/insert');
+    $this->clickLink("Link replaceWith $render_type");
+    $assert->assertWaitOnAjaxRequest();
+    $assert->responseContains($expected);
+    $assert->responseNotContains($this->wrapAjaxTarget($expected));
+  }
+
+  /**
+   * Provides test data for ::testInsert().
+   */
+  public function providerTestInsert() {
+    $test_cases = [];
+
+    // Test that no additional wrapper is added when inserting already wrapped
+    // response data and all top-level node elements (context) are processed
+    // correctly.
+    $test_cases['pre_wrapped'] = [
+      'pre-wrapped',
+      '<div class="pre-wrapped processed">pre-wrapped<script> var test;</script></div>',
+    ];
+    // Test that no additional empty leading div is added when the return
+    // value had a leading space and all top-level node elements (context) are
+    // processed correctly.
+    $test_cases['pre_wrapped_whitespace'] = [
+      'pre-wrapped-whitespace',
+      '<div class="pre-wrapped-whitespace processed">pre-wrapped-whitespace</div>',
+    ];
+    // Test that not wrapped response data (text node) is inserted wrapped and
+    // all top-level node elements (context) are processed correctly.
+    $test_cases['not_wrapped'] = [
+      'not-wrapped',
+      '<span class="processed">not-wrapped</span>',
+    ];
+    // Test that not wrapped response data (text node and comment node) is
+    // inserted wrapped and all top-level node elements
+    // (context) are processed correctly.
+    $test_cases['comment_string_not_wrapped'] = [
+      'comment-string-not-wrapped',
+      '<span class="processed"><!-- COMMENT -->comment-string-not-wrapped</span>',
+    ];
+    // Test that top-level comments (which are not lead by text nodes) are
+    // inserted without wrapper.
+    $test_cases['comment_not_wrapped'] = [
+      'comment-not-wrapped',
+      '<!-- COMMENT --><div class="comment-not-wrapped processed">comment-not-wrapped</div>',
+    ];
+    // Test that wrappend and not-wrapped response data is inserted correctly
+    // and all top-level node elements (context) are processed correctly.
+    $test_cases['mixed'] = [
+      'mixed',
+      '<div class="processed"> foo <!-- COMMENT -->  foo bar<div class="a class"><p>some string</p></div> additional not wrapped strings, <!-- ANOTHER COMMENT --> <p>final string</p></div>',
+    ];
+    // Test that when the response has only top-level node elements, they
+    // are processed properly without extra wrapping.
+    $test_cases['top_level_only'] = [
+      'top-level-only',
+      '<div class="processed">element #1</div><div class="processed">element #2</div>',
+    ];
+    // Test that whitespaces at start or end don't wrap the response when
+    // there are multiple top-level nodes.
+    $test_cases['top_level_only_pre_whitespace'] = [
+      'top-level-only-pre-whitespace',
+      '<div class="processed">element #1</div><div class="processed">element #2</div>',
+    ];
+    // Test that when there are whitespaces between top-level nodes, the
+    // response is wrapped.
+    $test_cases['top_level_only_middle_whitespace'] = [
+      'top-level-only-middle-whitespace',
+      '<div class="processed"><div>element #1</div> <div>element #2</div></div>',
+    ];
+    // Test that inline response data.
+    $test_cases['inline'] = [
+      'inline',
+      '<span class="processed">inline <div>BLOCK LEVEL<script> var test;</script></div></span>',
+    ];
+    // Test that empty response data.
+    $test_cases['empty'] = [
+      'empty',
+      '<span class="processed"></span>',
+    ];
+    return $test_cases;
+  }
+
 }