diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php
index 85c8ef3..be91cc0 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockTypeFormController.php
@@ -57,7 +57,6 @@ public function form(array $form, array &$form_state) {
         '#type' => 'details',
         '#title' => t('Language settings'),
         '#group' => 'additional_settings',
-        '#open' => TRUE,
       );
 
       $language_configuration = language_get_default_configuration('custom_block', $block_type->id());
diff --git a/core/modules/block/lib/Drupal/block/BlockFormController.php b/core/modules/block/lib/Drupal/block/BlockFormController.php
index 81a7cd3..c87c127 100644
--- a/core/modules/block/lib/Drupal/block/BlockFormController.php
+++ b/core/modules/block/lib/Drupal/block/BlockFormController.php
@@ -60,7 +60,6 @@ public function form(array $form, array &$form_state) {
       '#title' => t('Pages'),
       '#group' => 'visibility',
       '#weight' => 0,
-      '#open' => TRUE,
     );
 
     // @todo remove this access check and inject it in some other way. In fact
@@ -123,7 +122,6 @@ public function form(array $form, array &$form_state) {
         '#title' => t('Languages'),
         '#group' => 'visibility',
         '#weight' => 5,
-        '#open' => TRUE,
       );
       // If there are multiple configurable language types, let the user pick
       // which one should be applied to this visibility setting. This way users
@@ -156,7 +154,6 @@ public function form(array $form, array &$form_state) {
       '#title' => t('Roles'),
       '#group' => 'visibility',
       '#weight' => 10,
-      '#open' => TRUE,
     );
     $form['visibility']['role']['roles'] = array(
       '#type' => 'checkboxes',
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index a643f17..b2b2cfb 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -424,7 +424,6 @@ function _book_add_form_elements(&$form, &$form_state, EntityInterface $node) {
       'library' => array(array('book', 'drupal.book')),
     ),
     '#tree' => TRUE,
-    '#open' => TRUE,
   );
   foreach (array('menu_name', 'mlid', 'nid', 'router_path', 'has_children', 'options', 'module', 'original_bid', 'parent_depth_limit') as $key) {
     $form['book'][$key] = array(
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index b3fb8d3..21686ab 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -1000,7 +1000,6 @@ function comment_form_node_type_form_alter(&$form, $form_state) {
       '#attached' => array(
         'library' => array(array('comment', 'drupal.comment')),
       ),
-      '#open' => TRUE,
     );
     // Unlike coment_form_node_form_alter(), all of these settings are applied
     // as defaults to all new nodes. Therefore, it would be wrong to use #states
@@ -1107,7 +1106,6 @@ function comment_form_node_form_alter(&$form, $form_state) {
       'library' => array(array('comment', 'drupal.comment')),
     ),
     '#weight' => 30,
-    '#open' => TRUE,
   );
   $comment_count = isset($node->nid) ? db_query('SELECT comment_count FROM {node_comment_statistics} WHERE nid = :nid', array(':nid' => $node->nid))->fetchField() : 0;
   $comment_settings = ($node->comment == COMMENT_NODE_HIDDEN && empty($comment_count)) ? COMMENT_NODE_CLOSED : $node->comment;
diff --git a/core/modules/comment/lib/Drupal/comment/CommentFormController.php b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
index 38c2a84..8ea5b27 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentFormController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
@@ -54,7 +54,6 @@ public function form(array $form, array &$form_state) {
       $form['author'] += array(
         '#type' => 'details',
         '#title' => t('Administration'),
-        '#open' => TRUE,
       );
     }
 
diff --git a/core/modules/dblog/dblog.admin.inc b/core/modules/dblog/dblog.admin.inc
index c40610a..ae7dab5 100644
--- a/core/modules/dblog/dblog.admin.inc
+++ b/core/modules/dblog/dblog.admin.inc
@@ -307,7 +307,6 @@ function dblog_clear_log_form($form) {
     '#type' => 'details',
     '#title' => t('Clear log messages'),
     '#description' => t('This will permanently remove the log messages from the database.'),
-    '#open' => TRUE,
   );
   $form['dblog_clear']['clear'] = array(
     '#type' => 'submit',
diff --git a/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
index cf77ae8..e4f7914 100644
--- a/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
+++ b/core/modules/field/lib/Drupal/field/Plugin/views/field/Field.php
@@ -461,7 +461,6 @@ function multiple_options_form(&$form, &$form_state) {
       '#type' => 'details',
       '#title' => t('Multiple field settings'),
       '#weight' => 5,
-      '#open' => TRUE,
     );
 
     $form['group_rows'] = array(
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php b/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php
index 1658dc7..d1069f5 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/DisplayOverview.php
@@ -387,7 +387,6 @@ public function buildForm(array $form, array &$form_state, $entity_type = NULL,
         $form['modes'] = array(
           '#type' => 'details',
           '#title' => t('Custom display settings'),
-          '#open' => TRUE,
         );
         // Collect options and default values for the 'Custom display settings'
         // checkboxes.
diff --git a/core/modules/language/language.admin.inc b/core/modules/language/language.admin.inc
index 37577d3..c966ccb 100644
--- a/core/modules/language/language.admin.inc
+++ b/core/modules/language/language.admin.inc
@@ -619,7 +619,6 @@ function language_negotiation_configure_browser_form($form, &$form_state) {
     '#type' => 'details',
     '#title' => t('Add a new mapping'),
     '#tree' => TRUE,
-    '#open' => TRUE,
   );
   $form['new_mapping']['browser_langcode'] = array(
     '#type' => 'textfield',
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 207b1d2..09dab97 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -183,7 +183,6 @@ function locale_translate_export_form($form, &$form_state) {
           ':input[name="langcode"]' => array('value' => Language::LANGCODE_SYSTEM),
         ),
       ),
-      '#open' => TRUE,
     );
     $form['content_options']['not_customized'] = array(
       '#type' => 'checkbox',
diff --git a/core/modules/menu/menu.module b/core/modules/menu/menu.module
index 2bd3d14..f507ea5 100644
--- a/core/modules/menu/menu.module
+++ b/core/modules/menu/menu.module
@@ -673,7 +673,6 @@ function menu_form_node_type_form_alter(&$form, $form_state) {
       'library' => array(array('menu', 'drupal.menu.admin')),
     ),
     '#group' => 'additional_settings',
-    '#open' => TRUE,
   );
   $form['menu']['menu_options'] = array(
     '#type' => 'checkboxes',
diff --git a/core/modules/node/content_types.inc b/core/modules/node/content_types.inc
index d4ee5f0..b28b388 100644
--- a/core/modules/node/content_types.inc
+++ b/core/modules/node/content_types.inc
@@ -194,7 +194,6 @@ function node_type_form($form, &$form_state, $type = NULL) {
     '#type' => 'details',
     '#title' => t('Publishing options'),
     '#group' => 'additional_settings',
-    '#open' => TRUE,
   );
   $form['workflow']['node_options'] = array('#type' => 'checkboxes',
     '#title' => t('Default options'),
@@ -212,7 +211,6 @@ function node_type_form($form, &$form_state, $type = NULL) {
       '#type' => 'details',
       '#title' => t('Language settings'),
       '#group' => 'additional_settings',
-      '#open' => TRUE,
     );
 
     $language_configuration = language_get_default_configuration('node', $type->type);
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index c331a47..69dd8a2 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -1938,7 +1938,6 @@ function node_form_block_form_alter(&$form, &$form_state) {
     '#title' => t('Content types'),
     '#group' => 'visibility',
     '#weight' => 5,
-    '#open' => TRUE,
   );
   $form['visibility']['node_type']['types'] = array(
     '#type' => 'checkboxes',
@@ -2217,7 +2216,6 @@ function node_form_search_form_alter(&$form, $form_state) {
       '#type' => 'details',
       '#title' => t('Advanced search'),
       '#attributes' => array('class' => array('search-advanced')),
-      '#open' => TRUE,
     );
     $form['advanced']['keywords-fieldset'] = array(
       '#type' => 'fieldset',
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php b/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php
index 1917cca..c1c85e8 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php
@@ -47,7 +47,6 @@ public function buildForm(array $form, array &$form_state) {
       '#type' => 'details',
       '#title' => t('HTTP authentication'),
       '#description' => t('HTTP auth settings to be used by the SimpleTest browser during testing. Useful when the site requires basic HTTP authentication.'),
-      '#open' => TRUE,
     );
     $form['httpauth']['simpletest_httpauth_method'] = array(
       '#type' => 'select',
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 51c0dc4..ab45e33 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -553,7 +553,7 @@ function system_element_info() {
     '#theme_wrappers' => array('fieldset'),
   );
   $types['details'] = array(
-    '#open' => FALSE,
+    '#open' => TRUE,
     '#value' => NULL,
     '#process' => array('form_process_group', 'ajax_process_form'),
     '#pre_render' => array('form_pre_render_details', 'form_pre_render_group'),
diff --git a/core/modules/system/tests/modules/design_test/form/details.inc b/core/modules/system/tests/modules/design_test/form/details.inc
index 0a28e32..a205c16 100644
--- a/core/modules/system/tests/modules/design_test/form/details.inc
+++ b/core/modules/system/tests/modules/design_test/form/details.inc
@@ -19,7 +19,6 @@ function design_test_form_details($form, &$form_state) {
         ':input[name="states-trigger"]' => array('checked' => TRUE),
       ),
     ),
-    '#open' => TRUE,
   );
 
   $form['collapsed'] = array(
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php b/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php
index d60f0cd..ceb95fb 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php
@@ -56,7 +56,6 @@ public function form(array $form, array &$form_state) {
       '#title' => t('Relations'),
       '#open' => ($vocabulary->hierarchy == TAXONOMY_HIERARCHY_MULTIPLE),
       '#weight' => 10,
-      '#open' => TRUE,
     );
 
     // taxonomy_get_tree and taxonomy_term_load_parents may contain large
diff --git a/core/modules/translation_entity/lib/Drupal/translation_entity/EntityTranslationController.php b/core/modules/translation_entity/lib/Drupal/translation_entity/EntityTranslationController.php
index 1f4a046..77a652e 100644
--- a/core/modules/translation_entity/lib/Drupal/translation_entity/EntityTranslationController.php
+++ b/core/modules/translation_entity/lib/Drupal/translation_entity/EntityTranslationController.php
@@ -170,7 +170,6 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
           '#value' => t('Change'),
           '#submit' => array(array($this, 'entityFormSourceChange')),
         ),
-        '#open' => TRUE,
       );
       foreach (language_list(Language::STATE_CONFIGURABLE) as $language) {
         if (isset($translations[$language->langcode])) {
@@ -229,7 +228,6 @@ public function entityFormAlter(array &$form, array &$form_state, EntityInterfac
         '#weight' => 10,
         '#access' => $this->getTranslationAccess($entity, $source_langcode ? 'create' : 'update'),
         '#multilingual' => TRUE,
-        '#open' => TRUE,
       );
 
       // A new translation is enabled by default.
diff --git a/core/modules/user/lib/Drupal/user/AccountSettingsForm.php b/core/modules/user/lib/Drupal/user/AccountSettingsForm.php
index 845e3bd..f9907a9 100644
--- a/core/modules/user/lib/Drupal/user/AccountSettingsForm.php
+++ b/core/modules/user/lib/Drupal/user/AccountSettingsForm.php
@@ -190,7 +190,6 @@ public function buildForm(array $form, array &$form_state) {
       '#open' => ($config->get('register') == USER_REGISTER_ADMINISTRATORS_ONLY),
       '#description' => t('Edit the welcome e-mail messages sent to new member accounts created by an administrator.') . ' ' . $email_token_help,
       '#group' => 'email',
-      '#open' => TRUE,
     );
     $form['email_admin_created']['user_mail_register_admin_created_subject'] = array(
       '#type' => 'textfield',
@@ -290,7 +289,6 @@ public function buildForm(array $form, array &$form_state) {
       '#title' => t('Account activation'),
       '#description' => t('Enable and edit e-mail messages sent to users upon account activation (when an administrator activates an account of a user who has already registered, on a site where administrative approval is required).') . ' ' . $email_token_help,
       '#group' => 'email',
-      '#open' => TRUE,
     );
     $form['email_activated']['user_mail_status_activated_notify'] = array(
       '#type' => 'checkbox',
@@ -324,7 +322,6 @@ public function buildForm(array $form, array &$form_state) {
       '#title' => t('Account blocked'),
       '#description' => t('Enable and edit e-mail messages sent to users when their accounts are blocked.') . ' ' . $email_token_help,
       '#group' => 'email',
-      '#open' => TRUE,
     );
     $form['email_blocked']['user_mail_status_blocked_notify'] = array(
       '#type' => 'checkbox',
@@ -358,7 +355,6 @@ public function buildForm(array $form, array &$form_state) {
       '#title' => t('Account cancellation confirmation'),
       '#description' => t('Edit the e-mail messages sent to users when they attempt to cancel their accounts.') . ' ' . $email_token_help,
       '#group' => 'email',
-      '#open' => TRUE,
     );
     $form['email_cancel_confirm']['user_mail_cancel_confirm_subject'] = array(
       '#type' => 'textfield',
@@ -378,7 +374,6 @@ public function buildForm(array $form, array &$form_state) {
       '#title' => t('Account canceled'),
       '#description' => t('Enable and edit e-mail messages sent to users when their accounts are canceled.') . ' ' . $email_token_help,
       '#group' => 'email',
-      '#open' => TRUE,
     );
     $form['email_canceled']['user_mail_status_canceled_notify'] = array(
       '#type' => 'checkbox',
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/HandlerBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/HandlerBase.php
index 4308f5a..eacb5ff 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/HandlerBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/HandlerBase.php
@@ -291,7 +291,6 @@ public function buildOptionsForm(&$form, &$form_state) {
       '#type' => 'details',
       '#title' => t('More'),
       '#weight' => 150,
-      '#open' => TRUE,
     );
     // Allow to alter the default values brought into the form.
     // @todo Do we really want to keep this hook.
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/area/AreaPluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/area/AreaPluginBase.php
index 3336000..e2e1cd5 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/area/AreaPluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/area/AreaPluginBase.php
@@ -113,7 +113,6 @@ public function tokenForm(&$form, &$form_state) {
             ':input[name="options[tokenize]"]' => array('checked' => TRUE),
           ),
         ),
-        '#open' => TRUE,
       );
       $form['tokens']['help'] = array(
         '#markup' => '<p>' . t('The following tokens are available. If you would like to have the characters \'[\' and \']\' use the html entity codes \'%5B\' or  \'%5D\' or they will get replaced with empty space.') . '</p>',
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/argument/ArgumentPluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/argument/ArgumentPluginBase.php
index a2dc023..f680a26 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/argument/ArgumentPluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/argument/ArgumentPluginBase.php
@@ -195,7 +195,6 @@ public function buildOptionsForm(&$form, &$form_state) {
       '#type' => 'details',
       '#title' => t('Exceptions'),
       '#fieldset' => 'no_argument',
-      '#open' => TRUE,
     );
     $form['exception']['value'] = array(
       '#type' => 'textfield',
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/field/FieldPluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/field/FieldPluginBase.php
index c697cf9..6a7a839 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/field/FieldPluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/field/FieldPluginBase.php
@@ -536,7 +536,6 @@ public function buildOptionsForm(&$form, &$form_state) {
       '#type' => 'details',
       '#title' => t('Style settings'),
       '#weight' => 99,
-      '#open' => TRUE,
     );
 
     $form['element_type_enable'] = array(
@@ -685,7 +684,6 @@ public function buildOptionsForm(&$form, &$form_state) {
       '#title' => t('Rewrite results'),
       '#type' => 'details',
       '#weight' => 100,
-      '#open' => TRUE,
     );
 
     if ($this->allowAdvancedRender()) {
@@ -900,7 +898,6 @@ public function buildOptionsForm(&$form, &$form_state) {
             ),
           ),
         ),
-        '#open' => TRUE,
       );
 
       $form['alter']['trim'] = array(
@@ -1026,7 +1023,6 @@ public function buildOptionsForm(&$form, &$form_state) {
       '#type' => 'details',
       '#title' => t('No results behavior'),
       '#weight' => 100,
-      '#open' => TRUE,
     );
 
     $form['empty'] = array(
diff --git a/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php b/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
index e88ba9c..60866be 100644
--- a/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
+++ b/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
@@ -495,7 +495,6 @@ public function getDisplayDetails($view, $display) {
           'third',
         ),
       ),
-      '#open' => TRUE,
     );
 
     // Collapse the details by default.