src/Render/BigPipe.php                             | 27 ++++++++++++++--------
 src/Render/Placeholder/BigPipeStrategy.php         | 23 ++++++++++--------
 .../Render/Placeholder/BigPipeStrategyTest.php     | 16 ++++++-------
 3 files changed, 39 insertions(+), 27 deletions(-)

diff --git a/src/Render/BigPipe.php b/src/Render/BigPipe.php
index 7099414..0b4250c 100644
--- a/src/Render/BigPipe.php
+++ b/src/Render/BigPipe.php
@@ -195,18 +195,26 @@ class BigPipe implements BigPipeInterface {
    *   BigPipe placeholders.
    */
   protected function sendNoJsPlaceholders($html, $no_js_placeholders, AttachedAssetsInterface $cumulative_assets) {
-    $fragments = explode('<div data-big-pipe-selector-nojs="', $html);
-    print array_shift($fragments);
-    ob_end_flush();
-    flush();
-
-    foreach ($fragments as $fragment) {
-      $t = explode('"></div>', $fragment, 2);
-      $placeholder = $t[0];
-      if (!isset($no_js_placeholders[$placeholder])) {
+    // Split the HTML on every no-JS placeholder string.
+    $prepare_for_preg_split = function ($placeholder_string) {
+      return '(' . preg_quote($placeholder_string, '/') . ')';
+    };
+    $preg_placeholder_strings = array_map($prepare_for_preg_split, array_keys($no_js_placeholders));
+    $fragments = preg_split('/' . implode('|', $preg_placeholder_strings) . '/', $html, NULL, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);
+    assert('count($fragments) % 2 === 1');
+
+    foreach ($fragments as $index => $fragment) {
+      // The fragments with an even index (0, 2, 4 …) contain HTML which needs
+      // to be printed and flushed right away. The rest of the logic in the loop
+      // handles the uneven indices (1, 3, 5 …) which contains placeholders.
+      if ($index % 2 === 0) {
+        print $fragment;
+        flush();
         continue;
       }
 
+      $placeholder = $fragment;
+      assert('isset($no_js_placeholders[$placeholder])');
       $token = Crypt::randomBytesBase64(55);
 
       // Render the placeholder, but include the cumulative settings assets, so
@@ -252,7 +260,6 @@ class BigPipe implements BigPipeInterface {
 
       // Send this embedded HTML response.
       print $html_response->getContent();
-      print $t[1];
       flush();
 
       // Another placeholder was rendered and sent, track the set of asset
diff --git a/src/Render/Placeholder/BigPipeStrategy.php b/src/Render/Placeholder/BigPipeStrategy.php
index 6ae4973..bf4ea76 100644
--- a/src/Render/Placeholder/BigPipeStrategy.php
+++ b/src/Render/Placeholder/BigPipeStrategy.php
@@ -132,13 +132,13 @@ class BigPipeStrategy implements PlaceholderStrategyInterface {
       // @see \Drupal\Core\Form\FormBuilder::renderFormTokenPlaceholder()
       // @see \Drupal\Core\Form\FormBuilder::renderPlaceholderFormAction()
       if ($placeholder[0] !== '<' || $placeholder !== Html::normalize($placeholder)) {
-        $overridden_placeholders[$placeholder] = static::createBigPipeNoJsPlaceholder($placeholder, $placeholder_elements);
+        $overridden_placeholders[$placeholder] = static::createBigPipeNoJsPlaceholder($placeholder, $placeholder_elements, TRUE);
       }
       else {
         // If the current request/session doesn't have JavaScript, fall back to
         // no-JS BigPipe.
         if ($this->requestStack->getCurrentRequest()->cookies->has(static::NOJS_COOKIE)) {
-          $overridden_placeholders[$placeholder] = static::createBigPipeNoJsPlaceholder($placeholder, $placeholder_elements);
+          $overridden_placeholders[$placeholder] = static::createBigPipeNoJsPlaceholder($placeholder, $placeholder_elements, FALSE);
         }
         else {
           $overridden_placeholders[$placeholder] = static::createBigPipeJsPlaceholder($placeholder, $placeholder_elements);
@@ -194,18 +194,23 @@ class BigPipeStrategy implements PlaceholderStrategyInterface {
    *   The original placeholder.
    * @param array $placeholder_render_array
    *   The render array for a placeholder.
+   * @param bool $placeholder_must_be_attribute_safe
+   *   Whether the placeholder must be safe for use in a HTML attribute (in case
+   *   it's a placeholder for a HTML attribute value or a subset of it).
    *
    * @return array
    *   The resulting BigPipe no-JS placeholder render array.
-   *
-   * @todo Figure out how to simplify this. Perhaps no new placeholder is in fact necessary?
-   * @todo Related, perhaps distinguish between "HTML" and "non-HTML (attr value)" use cases? Because right now, this *breaks* HTML and therefore breaks response filters: this indiscriminately uses a <div> as a placeholder, which is invalid inside a HTML attribute, and thus breaks DOM parsing.
    */
-  protected static function createBigPipeNoJsPlaceholder($original_placeholder, array $placeholder_render_array) {
-    $big_pipe_placeholder_id = static::generateBigPipePlaceholderId($original_placeholder, $placeholder_render_array);
+  protected static function createBigPipeNoJsPlaceholder($original_placeholder, array $placeholder_render_array, $placeholder_must_be_attribute_safe = FALSE) {
+    if (!$placeholder_must_be_attribute_safe) {
+      $big_pipe_placeholder = '<div data-big-pipe-nojs-placeholder-id="' . Html::escape(static::generateBigPipePlaceholderId($original_placeholder, $placeholder_render_array))  . '"></div>';
+    }
+    else {
+      $big_pipe_placeholder = 'big_pipe_nojs_placeholder_attribute_safe:' . Html::escape($original_placeholder);
+    }
 
     return [
-      '#markup' => '<div data-big-pipe-nojs-placeholder-id="' . $big_pipe_placeholder_id . '"></div>',
+      '#markup' => $big_pipe_placeholder,
       '#cache' => [
         'max-age' => 0,
         'contexts' => [
@@ -214,7 +219,7 @@ class BigPipeStrategy implements PlaceholderStrategyInterface {
       ],
       '#attached' => [
         'big_pipe_nojs_placeholders' => [
-          $big_pipe_placeholder_id => $placeholder_render_array,
+          $big_pipe_placeholder => $placeholder_render_array,
         ],
       ],
     ];
diff --git a/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php b/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
index 35babb8..48cb167 100644
--- a/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
+++ b/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
@@ -90,11 +90,11 @@ class BigPipeStrategyTest extends UnitTestCase {
       ],
     ];
     $messages_big_pipe_nojs_placeholder = [
-      '#markup' => '<div data-big-pipe-nojs-placeholder-id="callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&args[0]&token=a8c34b5e"></div>',
+      '#markup' => '<div data-big-pipe-nojs-placeholder-id="callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]&amp;token=a8c34b5e"></div>',
       '#cache' => $cacheability_depends_on_session_and_nojs_cookie,
       '#attached' => [
         'big_pipe_nojs_placeholders' => [
-          'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&args[0]&token=a8c34b5e' => $placeholders[$messages_placeholder_markup],
+          '<div data-big-pipe-nojs-placeholder-id="callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]&amp;token=a8c34b5e"></div>' => $placeholders[$messages_placeholder_markup],
         ],
       ],
     ];
@@ -104,11 +104,11 @@ class BigPipeStrategyTest extends UnitTestCase {
       '#lazy_builder' => ['form_builder:renderPlaceholderFormAction', []],
     ];
     $form_action_big_pipe_nojs_placeholder = [
-      '#markup' => '<div data-big-pipe-nojs-placeholder-id="callback=form_builder%3ArenderPlaceholderFormAction&&token=e8cb6dae"></div>',
+      '#markup' => 'big_pipe_nojs_placeholder_attribute_safe:form_action_cc611e1d',
       '#cache' => $cacheability_depends_on_session_only,
       '#attached' => [
         'big_pipe_nojs_placeholders' => [
-          'callback=form_builder%3ArenderPlaceholderFormAction&&token=e8cb6dae' => $placeholders['form_action_cc611e1d'],
+          'big_pipe_nojs_placeholder_attribute_safe:form_action_cc611e1d' => $placeholders['form_action_cc611e1d'],
         ],
       ],
     ];
@@ -121,11 +121,11 @@ class BigPipeStrategyTest extends UnitTestCase {
       ],
     ];
     $csrf_token_big_pipe_nojs_placeholder = [
-      '#markup' => '<div data-big-pipe-nojs-placeholder-id="callback=route_processor_csrf%3ArenderPlaceholderCsrfToken&args[0]=admin/config/user-interface/shortcut/manage/default/add-link-inline&token=77d1dce6"></div>',
+      '#markup' => 'big_pipe_nojs_placeholder_attribute_safe:22dcc695f4a22e809a62d8eb7addd6fccecfbf31',
       '#cache' => $cacheability_depends_on_session_only,
       '#attached' => [
         'big_pipe_nojs_placeholders' => [
-          'callback=route_processor_csrf%3ArenderPlaceholderCsrfToken&args[0]=admin/config/user-interface/shortcut/manage/default/add-link-inline&token=77d1dce6' => $placeholders['22dcc695f4a22e809a62d8eb7addd6fccecfbf31'],
+          'big_pipe_nojs_placeholder_attribute_safe:22dcc695f4a22e809a62d8eb7addd6fccecfbf31' => $placeholders['22dcc695f4a22e809a62d8eb7addd6fccecfbf31'],
         ],
       ],
     ];
@@ -139,11 +139,11 @@ class BigPipeStrategyTest extends UnitTestCase {
       ],
     ];
     $hello_big_pipe_nojs_placeholder = [
-      '#markup' => '<div data-big-pipe-nojs-placeholder-id="callback=hello_or_yarhar&&token=d4524bc8"></div>',
+      '#markup' => 'big_pipe_nojs_placeholder_attribute_safe:&lt;hello',
       '#cache' => $cacheability_depends_on_session_only,
       '#attached' => [
         'big_pipe_nojs_placeholders' => [
-          'callback=hello_or_yarhar&&token=d4524bc8' => $placeholders['<hello'],
+          'big_pipe_nojs_placeholder_attribute_safe:&lt;hello' => $placeholders['<hello'],
         ],
       ],
     ];