diff --git a/core/lib/Drupal/Core/Entity/BundleEntityFormBase.php b/core/lib/Drupal/Core/Entity/BundleEntityFormBase.php
index f51dd36..fbafc50 100644
--- a/core/lib/Drupal/Core/Entity/BundleEntityFormBase.php
+++ b/core/lib/Drupal/Core/Entity/BundleEntityFormBase.php
@@ -4,6 +4,8 @@

 /**
  * Class BundleEntityFormBase is a base form for bundle config entities.
+ *
+ * @internal
  */
 class BundleEntityFormBase extends EntityForm {

diff --git a/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php b/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php
index bc0bdf3..dc0eacd 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php
@@ -8,6 +8,8 @@

 /**
  * Provides a generic base class for an entity-based confirmation form.
+ *
+ * @internal
  */
 abstract class ContentEntityConfirmFormBase extends ContentEntityForm implements ConfirmFormInterface {

diff --git a/core/lib/Drupal/Core/Entity/ContentEntityDeleteForm.php b/core/lib/Drupal/Core/Entity/ContentEntityDeleteForm.php
index 9a70ef5..32c48d8 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityDeleteForm.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityDeleteForm.php
@@ -7,6 +7,8 @@
 /**
  * Provides a generic base class for a content entity deletion form.
  *
+ * @internal
+ *
  * @todo Re-evaluate and streamline the entity deletion form class hierarchy in
  *   https://www.drupal.org/node/2491057.
  */
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityForm.php b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
index 14e910d..d2ebe28 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityForm.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
@@ -11,6 +11,8 @@
 /**
  * Entity form variant for content entity types.
  *
+ * @internal
+ *
  * @see \Drupal\Core\ContentEntityBase
  */
 class ContentEntityForm extends EntityForm implements ContentEntityFormInterface {
diff --git a/core/lib/Drupal/Core/Entity/EntityConfirmFormBase.php b/core/lib/Drupal/Core/Entity/EntityConfirmFormBase.php
index d8c39e4..be56dc8 100644
--- a/core/lib/Drupal/Core/Entity/EntityConfirmFormBase.php
+++ b/core/lib/Drupal/Core/Entity/EntityConfirmFormBase.php
@@ -10,6 +10,8 @@
  * Provides a generic base class for an entity-based confirmation form.
  *
  * @ingroup entity_api
+ *
+ * @internal
  */
 abstract class EntityConfirmFormBase extends EntityForm implements ConfirmFormInterface {

diff --git a/core/lib/Drupal/Core/Entity/EntityDeleteForm.php b/core/lib/Drupal/Core/Entity/EntityDeleteForm.php
index b7a66e3..6dd08f2 100644
--- a/core/lib/Drupal/Core/Entity/EntityDeleteForm.php
+++ b/core/lib/Drupal/Core/Entity/EntityDeleteForm.php
@@ -9,6 +9,8 @@
  * Provides a generic base class for an entity deletion form.
  *
  * @ingroup entity_api
+ *
+ * @internal
  */
 class EntityDeleteForm extends EntityConfirmFormBase {

diff --git a/core/lib/Drupal/Core/Entity/EntityForm.php b/core/lib/Drupal/Core/Entity/EntityForm.php
index 3506218..93e7f8a 100644
--- a/core/lib/Drupal/Core/Entity/EntityForm.php
+++ b/core/lib/Drupal/Core/Entity/EntityForm.php
@@ -12,6 +12,8 @@
  * Base class for entity forms.
  *
  * @ingroup entity_api
+ *
+ * @internal
  */
 class EntityForm extends FormBase implements EntityFormInterface {

diff --git a/core/lib/Drupal/Core/FileTransfer/Form/FileTransferAuthorizeForm.php b/core/lib/Drupal/Core/FileTransfer/Form/FileTransferAuthorizeForm.php
index 2adbd1f..3f8fd6d 100644
--- a/core/lib/Drupal/Core/FileTransfer/Form/FileTransferAuthorizeForm.php
+++ b/core/lib/Drupal/Core/FileTransfer/Form/FileTransferAuthorizeForm.php
@@ -10,6 +10,8 @@

 /**
  * Provides the file transfer authorization form.
+ *
+ * @internal
  */
 class FileTransferAuthorizeForm extends FormBase {

diff --git a/core/lib/Drupal/Core/Form/ConfigFormBase.php b/core/lib/Drupal/Core/Form/ConfigFormBase.php
index e7878a7..9426ea2 100644
--- a/core/lib/Drupal/Core/Form/ConfigFormBase.php
+++ b/core/lib/Drupal/Core/Form/ConfigFormBase.php
@@ -7,6 +7,8 @@

 /**
  * Base class for implementing system configuration forms.
+ *
+ * @internal
  */
 abstract class ConfigFormBase extends FormBase {
   use ConfigFormBaseTrait;
diff --git a/core/lib/Drupal/Core/Form/ConfirmFormBase.php b/core/lib/Drupal/Core/Form/ConfirmFormBase.php
index 4214bfc..3ee6893 100644
--- a/core/lib/Drupal/Core/Form/ConfirmFormBase.php
+++ b/core/lib/Drupal/Core/Form/ConfirmFormBase.php
@@ -4,6 +4,8 @@

 /**
  * Provides an generic base class for a confirmation form.
+ *
+ * @internal
  */
 abstract class ConfirmFormBase extends FormBase implements ConfirmFormInterface {

diff --git a/core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php b/core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php
index 686b1a2..55b7cbe 100644
--- a/core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php
@@ -13,6 +13,8 @@
  *
  * Note that hardcoded text provided by this form is not translated. This is
  * because translations are downloaded as a result of submitting this form.
+ *
+ * @internal
  */
 class SelectLanguageForm extends FormBase {

diff --git a/core/lib/Drupal/Core/Installer/Form/SelectProfileForm.php b/core/lib/Drupal/Core/Installer/Form/SelectProfileForm.php
index 679e6db..ea209ad 100644
--- a/core/lib/Drupal/Core/Installer/Form/SelectProfileForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SelectProfileForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the profile selection form.
+ *
+ * @internal
  */
 class SelectProfileForm extends FormBase {

diff --git a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
index c28b7f8..75bae9d 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides the site configuration form.
+ *
+ * @internal
  */
 class SiteConfigureForm extends ConfigFormBase {

diff --git a/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php b/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
index 5442d15..2259b42 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
@@ -11,6 +11,8 @@

 /**
  * Provides a form to configure and rewrite settings.php.
+ *
+ * @internal
  */
 class SiteSettingsForm extends FormBase {

diff --git a/core/modules/action/src/ActionAddForm.php b/core/modules/action/src/ActionAddForm.php
index 25aaebc..e7dbb8c 100644
--- a/core/modules/action/src/ActionAddForm.php
+++ b/core/modules/action/src/ActionAddForm.php
@@ -10,6 +10,8 @@

 /**
  * Provides a form for action add forms.
+ *
+ * @internal
  */
 class ActionAddForm extends ActionFormBase {

diff --git a/core/modules/action/src/ActionEditForm.php b/core/modules/action/src/ActionEditForm.php
index 8053605..01f5a9d 100644
--- a/core/modules/action/src/ActionEditForm.php
+++ b/core/modules/action/src/ActionEditForm.php
@@ -4,6 +4,8 @@

 /**
  * Provides a form for action edit forms.
+ *
+ * @internal
  */
 class ActionEditForm extends ActionFormBase {

diff --git a/core/modules/action/src/ActionFormBase.php b/core/modules/action/src/ActionFormBase.php
index 3fafd03..b649b88 100644
--- a/core/modules/action/src/ActionFormBase.php
+++ b/core/modules/action/src/ActionFormBase.php
@@ -10,6 +10,8 @@

 /**
  * Provides a base form for action forms.
+ *
+ * @internal
  */
 abstract class ActionFormBase extends EntityForm {

diff --git a/core/modules/action/src/Form/ActionAdminManageForm.php b/core/modules/action/src/Form/ActionAdminManageForm.php
index 478e919..08d2e7c 100644
--- a/core/modules/action/src/Form/ActionAdminManageForm.php
+++ b/core/modules/action/src/Form/ActionAdminManageForm.php
@@ -10,6 +10,8 @@

 /**
  * Provides a configuration form for configurable actions.
+ *
+ * @internal
  */
 class ActionAdminManageForm extends FormBase {

diff --git a/core/modules/action/src/Form/ActionDeleteForm.php b/core/modules/action/src/Form/ActionDeleteForm.php
index 9e7f0a5..0821b90 100644
--- a/core/modules/action/src/Form/ActionDeleteForm.php
+++ b/core/modules/action/src/Form/ActionDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a form to delete an action.
+ *
+ * @internal
  */
 class ActionDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/aggregator/src/FeedForm.php b/core/modules/aggregator/src/FeedForm.php
index 1580a30..aed2cd1 100644
--- a/core/modules/aggregator/src/FeedForm.php
+++ b/core/modules/aggregator/src/FeedForm.php
@@ -8,6 +8,8 @@

 /**
  * Form handler for the aggregator feed edit forms.
+ *
+ * @internal
  */
 class FeedForm extends ContentEntityForm {

diff --git a/core/modules/aggregator/src/Form/FeedDeleteForm.php b/core/modules/aggregator/src/Form/FeedDeleteForm.php
index 17a1798..53eaf3c 100644
--- a/core/modules/aggregator/src/Form/FeedDeleteForm.php
+++ b/core/modules/aggregator/src/Form/FeedDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a form for deleting a feed.
+ *
+ * @internal
  */
 class FeedDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/aggregator/src/Form/FeedItemsDeleteForm.php b/core/modules/aggregator/src/Form/FeedItemsDeleteForm.php
index 48c83dc..9f4087e 100644
--- a/core/modules/aggregator/src/Form/FeedItemsDeleteForm.php
+++ b/core/modules/aggregator/src/Form/FeedItemsDeleteForm.php
@@ -8,6 +8,8 @@

 /**
  * Provides a deletion confirmation form for items that belong to a feed.
+ *
+ * @internal
  */
 class FeedItemsDeleteForm extends ContentEntityConfirmFormBase {

diff --git a/core/modules/aggregator/src/Form/OpmlFeedAdd.php b/core/modules/aggregator/src/Form/OpmlFeedAdd.php
index 59e70d9..60a1899 100644
--- a/core/modules/aggregator/src/Form/OpmlFeedAdd.php
+++ b/core/modules/aggregator/src/Form/OpmlFeedAdd.php
@@ -12,6 +12,8 @@

 /**
  * Imports feeds from OPML.
+ *
+ * @internal
  */
 class OpmlFeedAdd extends FormBase {

diff --git a/core/modules/aggregator/src/Form/SettingsForm.php b/core/modules/aggregator/src/Form/SettingsForm.php
index 48b2dfe..3014c5b 100644
--- a/core/modules/aggregator/src/Form/SettingsForm.php
+++ b/core/modules/aggregator/src/Form/SettingsForm.php
@@ -13,6 +13,8 @@

 /**
  * Configures aggregator settings for this site.
+ *
+ * @internal
  */
 class SettingsForm extends ConfigFormBase {

diff --git a/core/modules/ban/src/Form/BanAdmin.php b/core/modules/ban/src/Form/BanAdmin.php
index 731d065..5d8e795 100644
--- a/core/modules/ban/src/Form/BanAdmin.php
+++ b/core/modules/ban/src/Form/BanAdmin.php
@@ -10,6 +10,8 @@

 /**
  * Displays banned IP addresses.
+ *
+ * @internal
  */
 class BanAdmin extends FormBase {

diff --git a/core/modules/ban/src/Form/BanDelete.php b/core/modules/ban/src/Form/BanDelete.php
index 3d14ca3..2d5731f 100644
--- a/core/modules/ban/src/Form/BanDelete.php
+++ b/core/modules/ban/src/Form/BanDelete.php
@@ -11,6 +11,8 @@

 /**
  * Provides a form to unban IP addresses.
+ *
+ * @internal
  */
 class BanDelete extends ConfirmFormBase {

diff --git a/core/modules/big_pipe/tests/modules/big_pipe_test/src/Form/BigPipeTestForm.php b/core/modules/big_pipe/tests/modules/big_pipe_test/src/Form/BigPipeTestForm.php
index c56ee32..7937ef5 100644
--- a/core/modules/big_pipe/tests/modules/big_pipe_test/src/Form/BigPipeTestForm.php
+++ b/core/modules/big_pipe/tests/modules/big_pipe_test/src/Form/BigPipeTestForm.php
@@ -4,7 +4,11 @@

 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
-
+/**
+ * Form to test BigPipe.
+ *
+ * @internal
+ */
 class BigPipeTestForm extends FormBase {

   /**
diff --git a/core/modules/block/src/BlockForm.php b/core/modules/block/src/BlockForm.php
index b2d180a..0416043 100644
--- a/core/modules/block/src/BlockForm.php
+++ b/core/modules/block/src/BlockForm.php
@@ -19,6 +19,8 @@

 /**
  * Provides form for block instance forms.
+ *
+ * @internal
  */
 class BlockForm extends EntityForm {

diff --git a/core/modules/block/src/Form/BlockDeleteForm.php b/core/modules/block/src/Form/BlockDeleteForm.php
index 5209b32..e128ea7 100644
--- a/core/modules/block/src/Form/BlockDeleteForm.php
+++ b/core/modules/block/src/Form/BlockDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a deletion confirmation form for the block instance deletion form.
+ *
+ * @internal
  */
 class BlockDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/block/tests/modules/block_test/src/Form/FavoriteAnimalTestForm.php b/core/modules/block/tests/modules/block_test/src/Form/FavoriteAnimalTestForm.php
index 9aa74c6..dbc9517 100644
--- a/core/modules/block/tests/modules/block_test/src/Form/FavoriteAnimalTestForm.php
+++ b/core/modules/block/tests/modules/block_test/src/Form/FavoriteAnimalTestForm.php
@@ -4,7 +4,11 @@

 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
-
+/**
+ * Form that performs favorite animal test.
+ *
+ * @internal
+ */
 class FavoriteAnimalTestForm extends FormBase {

   /**
diff --git a/core/modules/block/tests/modules/block_test/src/Form/TestForm.php b/core/modules/block/tests/modules/block_test/src/Form/TestForm.php
index 08fd6f6..1d78955 100644
--- a/core/modules/block/tests/modules/block_test/src/Form/TestForm.php
+++ b/core/modules/block/tests/modules/block_test/src/Form/TestForm.php
@@ -4,7 +4,11 @@

 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
-
+/**
+ * Form that performs base block form test.
+ *
+ * @internal
+ */
 class TestForm extends FormBase {

   /**
diff --git a/core/modules/block_content/src/BlockContentForm.php b/core/modules/block_content/src/BlockContentForm.php
index eefd4e9..225dc91 100644
--- a/core/modules/block_content/src/BlockContentForm.php
+++ b/core/modules/block_content/src/BlockContentForm.php
@@ -8,6 +8,8 @@

 /**
  * Form handler for the custom block edit forms.
+ *
+ * @internal
  */
 class BlockContentForm extends ContentEntityForm {

diff --git a/core/modules/block_content/src/BlockContentTypeForm.php b/core/modules/block_content/src/BlockContentTypeForm.php
index 4e140b1..6e17a62 100644
--- a/core/modules/block_content/src/BlockContentTypeForm.php
+++ b/core/modules/block_content/src/BlockContentTypeForm.php
@@ -9,6 +9,8 @@

 /**
  * Base form for category edit forms.
+ *
+ * @internal
  */
 class BlockContentTypeForm extends BundleEntityFormBase {

diff --git a/core/modules/block_content/src/Form/BlockContentDeleteForm.php b/core/modules/block_content/src/Form/BlockContentDeleteForm.php
index 035ec4c..fe0759c 100644
--- a/core/modules/block_content/src/Form/BlockContentDeleteForm.php
+++ b/core/modules/block_content/src/Form/BlockContentDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a confirmation form for deleting a custom block entity.
+ *
+ * @internal
  */
 class BlockContentDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/block_content/src/Form/BlockContentTypeDeleteForm.php b/core/modules/block_content/src/Form/BlockContentTypeDeleteForm.php
index aea4ab5..34da0a9 100644
--- a/core/modules/block_content/src/Form/BlockContentTypeDeleteForm.php
+++ b/core/modules/block_content/src/Form/BlockContentTypeDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a confirmation form for deleting a custom block type entity.
+ *
+ * @internal
  */
 class BlockContentTypeDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/book/src/Form/BookAdminEditForm.php b/core/modules/book/src/Form/BookAdminEditForm.php
index e91f52e..bab7673 100644
--- a/core/modules/book/src/Form/BookAdminEditForm.php
+++ b/core/modules/book/src/Form/BookAdminEditForm.php
@@ -15,6 +15,8 @@

 /**
  * Provides a form for administering a single book's hierarchy.
+ *
+ * @internal
  */
 class BookAdminEditForm extends FormBase {

diff --git a/core/modules/book/src/Form/BookOutlineForm.php b/core/modules/book/src/Form/BookOutlineForm.php
index 1d63aac..f7ea043 100644
--- a/core/modules/book/src/Form/BookOutlineForm.php
+++ b/core/modules/book/src/Form/BookOutlineForm.php
@@ -13,6 +13,8 @@

 /**
  * Displays the book outline form.
+ *
+ * @internal
  */
 class BookOutlineForm extends ContentEntityForm {

diff --git a/core/modules/book/src/Form/BookRemoveForm.php b/core/modules/book/src/Form/BookRemoveForm.php
index e31c094..f61aa77 100644
--- a/core/modules/book/src/Form/BookRemoveForm.php
+++ b/core/modules/book/src/Form/BookRemoveForm.php
@@ -10,6 +10,8 @@

 /**
  * Remove form for book module.
+ *
+ * @internal
  */
 class BookRemoveForm extends ConfirmFormBase {

diff --git a/core/modules/book/src/Form/BookSettingsForm.php b/core/modules/book/src/Form/BookSettingsForm.php
index 29590cc..3189ef5 100644
--- a/core/modules/book/src/Form/BookSettingsForm.php
+++ b/core/modules/book/src/Form/BookSettingsForm.php
@@ -7,6 +7,8 @@

 /**
  * Configure book settings for this site.
+ *
+ * @internal
  */
 class BookSettingsForm extends ConfigFormBase {

diff --git a/core/modules/ckeditor/tests/modules/src/Form/AjaxCssForm.php b/core/modules/ckeditor/tests/modules/src/Form/AjaxCssForm.php
index 7b6d592..e8c0668 100644
--- a/core/modules/ckeditor/tests/modules/src/Form/AjaxCssForm.php
+++ b/core/modules/ckeditor/tests/modules/src/Form/AjaxCssForm.php
@@ -9,6 +9,8 @@

 /**
  * A form for testing delivery of CSS to CKEditor via AJAX.
+ *
+ * @internal
  */
 class AjaxCssForm extends FormBase {

diff --git a/core/modules/comment/src/CommentForm.php b/core/modules/comment/src/CommentForm.php
index 28231b8..98e9dde 100644
--- a/core/modules/comment/src/CommentForm.php
+++ b/core/modules/comment/src/CommentForm.php
@@ -18,6 +18,8 @@

 /**
  * Base handler for comment forms.
+ *
+ * @internal
  */
 class CommentForm extends ContentEntityForm {

diff --git a/core/modules/comment/src/CommentTypeForm.php b/core/modules/comment/src/CommentTypeForm.php
index 9cb147f..0ac5b44 100644
--- a/core/modules/comment/src/CommentTypeForm.php
+++ b/core/modules/comment/src/CommentTypeForm.php
@@ -12,6 +12,8 @@

 /**
  * Base form handler for comment type edit forms.
+ *
+ * @internal
  */
 class CommentTypeForm extends EntityForm {

diff --git a/core/modules/comment/src/Form/CommentAdminOverview.php b/core/modules/comment/src/Form/CommentAdminOverview.php
index 24f8b0a..f523882 100644
--- a/core/modules/comment/src/Form/CommentAdminOverview.php
+++ b/core/modules/comment/src/Form/CommentAdminOverview.php
@@ -14,6 +14,8 @@

 /**
  * Provides the comments overview administration form.
+ *
+ * @internal
  */
 class CommentAdminOverview extends FormBase {

diff --git a/core/modules/comment/src/Form/CommentTypeDeleteForm.php b/core/modules/comment/src/Form/CommentTypeDeleteForm.php
index 30181c1..ded5b23 100644
--- a/core/modules/comment/src/Form/CommentTypeDeleteForm.php
+++ b/core/modules/comment/src/Form/CommentTypeDeleteForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a confirmation form for deleting a comment type entity.
+ *
+ * @internal
  */
 class CommentTypeDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/comment/src/Form/ConfirmDeleteMultiple.php b/core/modules/comment/src/Form/ConfirmDeleteMultiple.php
index 5906248..b2a45f2 100644
--- a/core/modules/comment/src/Form/ConfirmDeleteMultiple.php
+++ b/core/modules/comment/src/Form/ConfirmDeleteMultiple.php
@@ -11,6 +11,8 @@

 /**
  * Provides the comment multiple delete confirmation form.
+ *
+ * @internal
  */
 class ConfirmDeleteMultiple extends ConfirmFormBase {

diff --git a/core/modules/comment/src/Form/DeleteForm.php b/core/modules/comment/src/Form/DeleteForm.php
index fa7ab9d..3b2028b 100644
--- a/core/modules/comment/src/Form/DeleteForm.php
+++ b/core/modules/comment/src/Form/DeleteForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides the comment delete confirmation form.
+ *
+ * @internal
  */
 class DeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/config/src/Form/ConfigExportForm.php b/core/modules/config/src/Form/ConfigExportForm.php
index e822f7f..4c5f150 100644
--- a/core/modules/config/src/Form/ConfigExportForm.php
+++ b/core/modules/config/src/Form/ConfigExportForm.php
@@ -7,6 +7,8 @@

 /**
  * Defines the configuration export form.
+ *
+ * @internal
  */
 class ConfigExportForm extends FormBase {

diff --git a/core/modules/config/src/Form/ConfigImportForm.php b/core/modules/config/src/Form/ConfigImportForm.php
index 0c3def8..6b7b557 100644
--- a/core/modules/config/src/Form/ConfigImportForm.php
+++ b/core/modules/config/src/Form/ConfigImportForm.php
@@ -10,6 +10,8 @@

 /**
  * Defines the configuration import form.
+ *
+ * @internal
  */
 class ConfigImportForm extends FormBase {

diff --git a/core/modules/config/src/Form/ConfigSingleExportForm.php b/core/modules/config/src/Form/ConfigSingleExportForm.php
index 8710655..b09ca9a 100644
--- a/core/modules/config/src/Form/ConfigSingleExportForm.php
+++ b/core/modules/config/src/Form/ConfigSingleExportForm.php
@@ -15,6 +15,8 @@

 /**
  * Provides a form for exporting a single configuration file.
+ *
+ * @internal
  */
 class ConfigSingleExportForm extends FormBase {

diff --git a/core/modules/config/src/Form/ConfigSingleImportForm.php b/core/modules/config/src/Form/ConfigSingleImportForm.php
index fcb3883..9f9a8d9 100644
--- a/core/modules/config/src/Form/ConfigSingleImportForm.php
+++ b/core/modules/config/src/Form/ConfigSingleImportForm.php
@@ -26,6 +26,8 @@

 /**
  * Provides a form for importing a single configuration file.
+ *
+ * @internal
  */
 class ConfigSingleImportForm extends ConfirmFormBase {

diff --git a/core/modules/config/src/Form/ConfigSync.php b/core/modules/config/src/Form/ConfigSync.php
index fe1b2e4..2813099 100644
--- a/core/modules/config/src/Form/ConfigSync.php
+++ b/core/modules/config/src/Form/ConfigSync.php
@@ -21,6 +21,8 @@

 /**
  * Construct the storage changes in a configuration synchronization form.
+ *
+ * @internal
  */
 class ConfigSync extends FormBase {

diff --git a/core/modules/config/tests/config_test/src/ConfigTestForm.php b/core/modules/config/tests/config_test/src/ConfigTestForm.php
index 6a56c3d..fbc0f96 100644
--- a/core/modules/config/tests/config_test/src/ConfigTestForm.php
+++ b/core/modules/config/tests/config_test/src/ConfigTestForm.php
@@ -8,6 +8,8 @@

 /**
  * Form controller for the test config edit forms.
+ *
+ * @internal
  */
 class ConfigTestForm extends EntityForm {

diff --git a/core/modules/config_translation/src/Form/ConfigTranslationAddForm.php b/core/modules/config_translation/src/Form/ConfigTranslationAddForm.php
index 9edcb8c..812b1a1 100644
--- a/core/modules/config_translation/src/Form/ConfigTranslationAddForm.php
+++ b/core/modules/config_translation/src/Form/ConfigTranslationAddForm.php
@@ -7,6 +7,8 @@

 /**
  * Defines a form for adding configuration translations.
+ *
+ * @internal
  */
 class ConfigTranslationAddForm extends ConfigTranslationFormBase {

diff --git a/core/modules/config_translation/src/Form/ConfigTranslationDeleteForm.php b/core/modules/config_translation/src/Form/ConfigTranslationDeleteForm.php
index ca3ad28..273b26c 100644
--- a/core/modules/config_translation/src/Form/ConfigTranslationDeleteForm.php
+++ b/core/modules/config_translation/src/Form/ConfigTranslationDeleteForm.php
@@ -15,6 +15,8 @@

 /**
  * Builds a form to delete configuration translation.
+ *
+ * @internal
  */
 class ConfigTranslationDeleteForm extends ConfirmFormBase {

diff --git a/core/modules/config_translation/src/Form/ConfigTranslationEditForm.php b/core/modules/config_translation/src/Form/ConfigTranslationEditForm.php
index 86a8f1c..cdbd9b8 100644
--- a/core/modules/config_translation/src/Form/ConfigTranslationEditForm.php
+++ b/core/modules/config_translation/src/Form/ConfigTranslationEditForm.php
@@ -7,6 +7,8 @@

 /**
  * Defines a form for editing configuration translations.
+ *
+ * @internal
  */
 class ConfigTranslationEditForm extends ConfigTranslationFormBase {

diff --git a/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php b/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php
index 9f95a76..0a8022e 100644
--- a/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php
+++ b/core/modules/config_translation/src/Form/ConfigTranslationFormBase.php
@@ -15,6 +15,8 @@

 /**
  * Provides a base form for configuration translations.
+ *
+ * @internal
  */
 abstract class ConfigTranslationFormBase extends FormBase implements BaseFormIdInterface {

diff --git a/core/modules/contact/src/ContactFormEditForm.php b/core/modules/contact/src/ContactFormEditForm.php
index aa94540..1df6953 100644
--- a/core/modules/contact/src/ContactFormEditForm.php
+++ b/core/modules/contact/src/ContactFormEditForm.php
@@ -15,6 +15,8 @@

 /**
  * Base form for contact form edit forms.
+ *
+ * @internal
  */
 class ContactFormEditForm extends EntityForm implements ContainerInjectionInterface {
   use ConfigFormBaseTrait;
diff --git a/core/modules/contact/src/MessageForm.php b/core/modules/contact/src/MessageForm.php
index 16d41b5..c555f3b 100644
--- a/core/modules/contact/src/MessageForm.php
+++ b/core/modules/contact/src/MessageForm.php
@@ -14,6 +14,8 @@

 /**
  * Form controller for contact message forms.
+ *
+ * @internal
  */
 class MessageForm extends ContentEntityForm {

diff --git a/core/modules/content_moderation/src/Form/EntityModerationForm.php b/core/modules/content_moderation/src/Form/EntityModerationForm.php
index ea2fedd..70abad9 100644
--- a/core/modules/content_moderation/src/Form/EntityModerationForm.php
+++ b/core/modules/content_moderation/src/Form/EntityModerationForm.php
@@ -13,6 +13,8 @@

 /**
  * The EntityModerationForm provides a simple UI for changing moderation state.
+ *
+ * @internal
  */
 class EntityModerationForm extends FormBase {

diff --git a/core/modules/content_translation/src/Form/ContentTranslationDeleteForm.php b/core/modules/content_translation/src/Form/ContentTranslationDeleteForm.php
index 9d225dc..bbbea44 100644
--- a/core/modules/content_translation/src/Form/ContentTranslationDeleteForm.php
+++ b/core/modules/content_translation/src/Form/ContentTranslationDeleteForm.php
@@ -8,6 +8,8 @@

 /**
  * Delete translation form for content_translation module.
+ *
+ * @internal
  */
 class ContentTranslationDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/dblog/src/Form/DblogClearLogConfirmForm.php b/core/modules/dblog/src/Form/DblogClearLogConfirmForm.php
index 0f420f0..46344eb 100644
--- a/core/modules/dblog/src/Form/DblogClearLogConfirmForm.php
+++ b/core/modules/dblog/src/Form/DblogClearLogConfirmForm.php
@@ -10,6 +10,8 @@

 /**
  * Provides a confirmation form before clearing out the logs.
+ *
+ * @internal
  */
 class DblogClearLogConfirmForm extends ConfirmFormBase {

diff --git a/core/modules/dblog/src/Form/DblogFilterForm.php b/core/modules/dblog/src/Form/DblogFilterForm.php
index c8de0fc..21619d6 100644
--- a/core/modules/dblog/src/Form/DblogFilterForm.php
+++ b/core/modules/dblog/src/Form/DblogFilterForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the database logging filter form.
+ *
+ * @internal
  */
 class DblogFilterForm extends FormBase {

diff --git a/core/modules/editor/src/Form/EditorImageDialog.php b/core/modules/editor/src/Form/EditorImageDialog.php
index 547032e..0e148d2 100644
--- a/core/modules/editor/src/Form/EditorImageDialog.php
+++ b/core/modules/editor/src/Form/EditorImageDialog.php
@@ -15,6 +15,8 @@

 /**
  * Provides an image dialog for text editors.
+ *
+ * @internal
  */
 class EditorImageDialog extends FormBase {

diff --git a/core/modules/editor/src/Form/EditorLinkDialog.php b/core/modules/editor/src/Form/EditorLinkDialog.php
index 724f413..5f34e10 100644
--- a/core/modules/editor/src/Form/EditorLinkDialog.php
+++ b/core/modules/editor/src/Form/EditorLinkDialog.php
@@ -12,6 +12,8 @@

 /**
  * Provides a link dialog for text editors.
+ *
+ * @internal
  */
 class EditorLinkDialog extends FormBase {

diff --git a/core/modules/field/tests/modules/field_test/src/Form/NestedEntityTestForm.php b/core/modules/field/tests/modules/field_test/src/Form/NestedEntityTestForm.php
index 949ffda..ed99a05 100644
--- a/core/modules/field/tests/modules/field_test/src/Form/NestedEntityTestForm.php
+++ b/core/modules/field/tests/modules/field_test/src/Form/NestedEntityTestForm.php
@@ -10,6 +10,8 @@

 /**
  * Provides a form for field_test routes.
+ *
+ * @internal
  */
 class NestedEntityTestForm extends FormBase {

diff --git a/core/modules/field_layout/src/Form/FieldLayoutEntityFormDisplayEditForm.php b/core/modules/field_layout/src/Form/FieldLayoutEntityFormDisplayEditForm.php
index c42a9d8..883cc9e 100644
--- a/core/modules/field_layout/src/Form/FieldLayoutEntityFormDisplayEditForm.php
+++ b/core/modules/field_layout/src/Form/FieldLayoutEntityFormDisplayEditForm.php
@@ -10,6 +10,8 @@

 /**
  * Edit form for the EntityFormDisplay entity type.
+ *
+ * @internal
  */
 class FieldLayoutEntityFormDisplayEditForm extends EntityFormDisplayEditForm {

diff --git a/core/modules/field_layout/src/Form/FieldLayoutEntityViewDisplayEditForm.php b/core/modules/field_layout/src/Form/FieldLayoutEntityViewDisplayEditForm.php
index 92bfbde..3fc50e4 100644
--- a/core/modules/field_layout/src/Form/FieldLayoutEntityViewDisplayEditForm.php
+++ b/core/modules/field_layout/src/Form/FieldLayoutEntityViewDisplayEditForm.php
@@ -10,6 +10,8 @@

 /**
  * Edit form for the EntityViewDisplay entity type.
+ *
+ * @internal
  */
 class FieldLayoutEntityViewDisplayEditForm extends EntityViewDisplayEditForm {

diff --git a/core/modules/field_ui/src/Form/EntityDisplayFormBase.php b/core/modules/field_ui/src/Form/EntityDisplayFormBase.php
index 0a91862..fd4c4f5 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayFormBase.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayFormBase.php
@@ -17,6 +17,8 @@

 /**
  * Base class for EntityDisplay edit forms.
+ *
+ * @internal
  */
 abstract class EntityDisplayFormBase extends EntityForm {

diff --git a/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
index ed1c5fe..67450e5 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the add form for entity display modes.
+ *
+ * @internal
  */
 class EntityDisplayModeAddForm extends EntityDisplayModeFormBase {

diff --git a/core/modules/field_ui/src/Form/EntityDisplayModeDeleteForm.php b/core/modules/field_ui/src/Form/EntityDisplayModeDeleteForm.php
index f7d8804..1dc7633 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayModeDeleteForm.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayModeDeleteForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides the delete form for entity display modes.
+ *
+ * @internal
  */
 class EntityDisplayModeDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/field_ui/src/Form/EntityDisplayModeEditForm.php b/core/modules/field_ui/src/Form/EntityDisplayModeEditForm.php
index 8a874da..d7fa552 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayModeEditForm.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayModeEditForm.php
@@ -4,6 +4,8 @@

 /**
  * Provides the edit form for entity display modes.
+ *
+ * @internal
  */
 class EntityDisplayModeEditForm extends EntityDisplayModeFormBase {

diff --git a/core/modules/field_ui/src/Form/EntityDisplayModeFormBase.php b/core/modules/field_ui/src/Form/EntityDisplayModeFormBase.php
index 72a8a19..56fd875 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayModeFormBase.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayModeFormBase.php
@@ -7,6 +7,8 @@

 /**
  * Provides the generic base class for entity display mode forms.
+ *
+ * @internal
  */
 abstract class EntityDisplayModeFormBase extends EntityForm {

diff --git a/core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php b/core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php
index 2c3e360..128742f 100644
--- a/core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php
+++ b/core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php
@@ -11,6 +11,8 @@

 /**
  * Edit form for the EntityFormDisplay entity type.
+ *
+ * @internal
  */
 class EntityFormDisplayEditForm extends EntityDisplayFormBase {

diff --git a/core/modules/field_ui/src/Form/EntityFormModeAddForm.php b/core/modules/field_ui/src/Form/EntityFormModeAddForm.php
index 9cecd83..cfcc6fb 100644
--- a/core/modules/field_ui/src/Form/EntityFormModeAddForm.php
+++ b/core/modules/field_ui/src/Form/EntityFormModeAddForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides the add form for entity display modes.
+ *
+ * @internal
  */
 class EntityFormModeAddForm extends EntityDisplayModeAddForm {

diff --git a/core/modules/field_ui/src/Form/EntityViewDisplayEditForm.php b/core/modules/field_ui/src/Form/EntityViewDisplayEditForm.php
index c27f3d4..5e2a8ce 100644
--- a/core/modules/field_ui/src/Form/EntityViewDisplayEditForm.php
+++ b/core/modules/field_ui/src/Form/EntityViewDisplayEditForm.php
@@ -11,6 +11,8 @@

 /**
  * Edit form for the EntityViewDisplay entity type.
+ *
+ * @internal
  */
 class EntityViewDisplayEditForm extends EntityDisplayFormBase {

diff --git a/core/modules/field_ui/src/Form/FieldConfigDeleteForm.php b/core/modules/field_ui/src/Form/FieldConfigDeleteForm.php
index 6778231..ab83e8f 100644
--- a/core/modules/field_ui/src/Form/FieldConfigDeleteForm.php
+++ b/core/modules/field_ui/src/Form/FieldConfigDeleteForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a form for removing a field from a bundle.
+ *
+ * @internal
  */
 class FieldConfigDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/field_ui/src/Form/FieldConfigEditForm.php b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
index 2895479..34868ad 100644
--- a/core/modules/field_ui/src/Form/FieldConfigEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a form for the field settings form.
+ *
+ * @internal
  */
 class FieldConfigEditForm extends EntityForm {

diff --git a/core/modules/field_ui/src/Form/FieldStorageAddForm.php b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
index e1f2787..97e3ce7 100644
--- a/core/modules/field_ui/src/Form/FieldStorageAddForm.php
+++ b/core/modules/field_ui/src/Form/FieldStorageAddForm.php
@@ -14,6 +14,8 @@

 /**
  * Provides a form for the "field storage" add page.
+ *
+ * @internal
  */
 class FieldStorageAddForm extends FormBase {

diff --git a/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php b/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php
index 49a45e1..94a8366 100644
--- a/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a form for the "field storage" edit page.
+ *
+ * @internal
  */
 class FieldStorageConfigEditForm extends EntityForm {

diff --git a/core/modules/file/tests/file_module_test/src/Form/FileModuleTestForm.php b/core/modules/file/tests/file_module_test/src/Form/FileModuleTestForm.php
index 9dc9d35..51353f6 100644
--- a/core/modules/file/tests/file_module_test/src/Form/FileModuleTestForm.php
+++ b/core/modules/file/tests/file_module_test/src/Form/FileModuleTestForm.php
@@ -7,6 +7,8 @@

 /**
  * Form controller for file_module_test module.
+ *
+ * @internal
  */
 class FileModuleTestForm extends FormBase {

diff --git a/core/modules/filter/src/FilterFormatAddForm.php b/core/modules/filter/src/FilterFormatAddForm.php
index cb9b598..39f1cb6 100644
--- a/core/modules/filter/src/FilterFormatAddForm.php
+++ b/core/modules/filter/src/FilterFormatAddForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a form for adding a filter format.
+ *
+ * @internal
  */
 class FilterFormatAddForm extends FilterFormatFormBase {

diff --git a/core/modules/filter/src/FilterFormatEditForm.php b/core/modules/filter/src/FilterFormatEditForm.php
index 9ffd8c8..8173a78 100644
--- a/core/modules/filter/src/FilterFormatEditForm.php
+++ b/core/modules/filter/src/FilterFormatEditForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a form for adding a filter format.
+ *
+ * @internal
  */
 class FilterFormatEditForm extends FilterFormatFormBase {

diff --git a/core/modules/filter/src/FilterFormatFormBase.php b/core/modules/filter/src/FilterFormatFormBase.php
index cbcb632..f7585f9 100644
--- a/core/modules/filter/src/FilterFormatFormBase.php
+++ b/core/modules/filter/src/FilterFormatFormBase.php
@@ -8,6 +8,8 @@

 /**
  * Provides a base form for a filter format.
+ *
+ * @internal
  */
 abstract class FilterFormatFormBase extends EntityForm {

diff --git a/core/modules/filter/src/Form/FilterDisableForm.php b/core/modules/filter/src/Form/FilterDisableForm.php
index c6e8294..a8a2ba3 100644
--- a/core/modules/filter/src/Form/FilterDisableForm.php
+++ b/core/modules/filter/src/Form/FilterDisableForm.php
@@ -8,6 +8,8 @@

 /**
  * Provides the filter format disable form.
+ *
+ * @internal
  */
 class FilterDisableForm extends EntityConfirmFormBase {

diff --git a/core/modules/filter/tests/filter_test/src/Form/FilterTestFormatForm.php b/core/modules/filter/tests/filter_test/src/Form/FilterTestFormatForm.php
index a5049a1..12e9b97 100644
--- a/core/modules/filter/tests/filter_test/src/Form/FilterTestFormatForm.php
+++ b/core/modules/filter/tests/filter_test/src/Form/FilterTestFormatForm.php
@@ -7,6 +7,8 @@

 /**
  * Shows a test form for testing the 'text_format' form element.
+ *
+ * @internal
  */
 class FilterTestFormatForm extends FormBase {

diff --git a/core/modules/forum/src/Form/ContainerForm.php b/core/modules/forum/src/Form/ContainerForm.php
index 0b01124..afcb1cc 100644
--- a/core/modules/forum/src/Form/ContainerForm.php
+++ b/core/modules/forum/src/Form/ContainerForm.php
@@ -6,6 +6,8 @@

 /**
  * Base form for container term edit forms.
+ *
+ * @internal
  */
 class ContainerForm extends ForumForm {

diff --git a/core/modules/forum/src/Form/DeleteForm.php b/core/modules/forum/src/Form/DeleteForm.php
index 5b3666a..c652410 100644
--- a/core/modules/forum/src/Form/DeleteForm.php
+++ b/core/modules/forum/src/Form/DeleteForm.php
@@ -9,6 +9,8 @@

 /**
  * Builds the form to delete a forum term.
+ *
+ * @internal
  */
 class DeleteForm extends ConfirmFormBase {

diff --git a/core/modules/forum/src/Form/ForumForm.php b/core/modules/forum/src/Form/ForumForm.php
index 9e5895d..c894d3f 100644
--- a/core/modules/forum/src/Form/ForumForm.php
+++ b/core/modules/forum/src/Form/ForumForm.php
@@ -8,6 +8,8 @@

 /**
  * Base form for forum term edit forms.
+ *
+ * @internal
  */
 class ForumForm extends TermForm {

diff --git a/core/modules/forum/src/Form/Overview.php b/core/modules/forum/src/Form/Overview.php
index df6f947..ac0d3a2 100644
--- a/core/modules/forum/src/Form/Overview.php
+++ b/core/modules/forum/src/Form/Overview.php
@@ -12,6 +12,8 @@

 /**
  * Provides forum overview form for the forum vocabulary.
+ *
+ * @internal
  */
 class Overview extends OverviewTerms {

diff --git a/core/modules/forum/src/ForumSettingsForm.php b/core/modules/forum/src/ForumSettingsForm.php
index 12bb551..f017f21 100644
--- a/core/modules/forum/src/ForumSettingsForm.php
+++ b/core/modules/forum/src/ForumSettingsForm.php
@@ -7,6 +7,8 @@

 /**
  * Configure forum settings for this site.
+ *
+ * @internal
  */
 class ForumSettingsForm extends ConfigFormBase {

diff --git a/core/modules/image/src/Form/ImageEffectAddForm.php b/core/modules/image/src/Form/ImageEffectAddForm.php
index ce30451..76f164c 100644
--- a/core/modules/image/src/Form/ImageEffectAddForm.php
+++ b/core/modules/image/src/Form/ImageEffectAddForm.php
@@ -9,6 +9,8 @@

 /**
  * Provides an add form for image effects.
+ *
+ * @internal
  */
 class ImageEffectAddForm extends ImageEffectFormBase {

diff --git a/core/modules/image/src/Form/ImageEffectDeleteForm.php b/core/modules/image/src/Form/ImageEffectDeleteForm.php
index 52cde33..e45f7a5 100644
--- a/core/modules/image/src/Form/ImageEffectDeleteForm.php
+++ b/core/modules/image/src/Form/ImageEffectDeleteForm.php
@@ -8,6 +8,8 @@

 /**
  * Form for deleting an image effect.
+ *
+ * @internal
  */
 class ImageEffectDeleteForm extends ConfirmFormBase {

diff --git a/core/modules/image/src/Form/ImageEffectEditForm.php b/core/modules/image/src/Form/ImageEffectEditForm.php
index 390e4dc..0dd362c 100644
--- a/core/modules/image/src/Form/ImageEffectEditForm.php
+++ b/core/modules/image/src/Form/ImageEffectEditForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides an edit form for image effects.
+ *
+ * @internal
  */
 class ImageEffectEditForm extends ImageEffectFormBase {

diff --git a/core/modules/image/src/Form/ImageEffectFormBase.php b/core/modules/image/src/Form/ImageEffectFormBase.php
index 74368d6..d2099c6 100644
--- a/core/modules/image/src/Form/ImageEffectFormBase.php
+++ b/core/modules/image/src/Form/ImageEffectFormBase.php
@@ -12,6 +12,8 @@

 /**
  * Provides a base form for image effects.
+ *
+ * @internal
  */
 abstract class ImageEffectFormBase extends FormBase {

diff --git a/core/modules/image/src/Form/ImageStyleAddForm.php b/core/modules/image/src/Form/ImageStyleAddForm.php
index 41261ca..e0f5654 100644
--- a/core/modules/image/src/Form/ImageStyleAddForm.php
+++ b/core/modules/image/src/Form/ImageStyleAddForm.php
@@ -6,6 +6,8 @@

 /**
  * Controller for image style addition forms.
+ *
+ * @internal
  */
 class ImageStyleAddForm extends ImageStyleFormBase {

diff --git a/core/modules/image/src/Form/ImageStyleDeleteForm.php b/core/modules/image/src/Form/ImageStyleDeleteForm.php
index c02c803..f49d6b8 100644
--- a/core/modules/image/src/Form/ImageStyleDeleteForm.php
+++ b/core/modules/image/src/Form/ImageStyleDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Creates a form to delete an image style.
+ *
+ * @internal
  */
 class ImageStyleDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/image/src/Form/ImageStyleEditForm.php b/core/modules/image/src/Form/ImageStyleEditForm.php
index 574d914..7f6227a 100644
--- a/core/modules/image/src/Form/ImageStyleEditForm.php
+++ b/core/modules/image/src/Form/ImageStyleEditForm.php
@@ -11,6 +11,8 @@

 /**
  * Controller for image style edit form.
+ *
+ * @internal
  */
 class ImageStyleEditForm extends ImageStyleFormBase {

diff --git a/core/modules/image/src/Form/ImageStyleFlushForm.php b/core/modules/image/src/Form/ImageStyleFlushForm.php
index 1326f88..df1d24e 100644
--- a/core/modules/image/src/Form/ImageStyleFlushForm.php
+++ b/core/modules/image/src/Form/ImageStyleFlushForm.php
@@ -7,6 +7,8 @@

 /**
  * Form controller for image style flush.
+ *
+ * @internal
  */
 class ImageStyleFlushForm extends EntityConfirmFormBase {

diff --git a/core/modules/image/src/Form/ImageStyleFormBase.php b/core/modules/image/src/Form/ImageStyleFormBase.php
index bf3210a..e35327c 100644
--- a/core/modules/image/src/Form/ImageStyleFormBase.php
+++ b/core/modules/image/src/Form/ImageStyleFormBase.php
@@ -9,6 +9,8 @@

 /**
  * Base form for image style add and edit forms.
+ *
+ * @internal
  */
 abstract class ImageStyleFormBase extends EntityForm {

diff --git a/core/modules/language/src/Form/ContentLanguageSettingsForm.php b/core/modules/language/src/Form/ContentLanguageSettingsForm.php
index 38aaffa..619d944 100644
--- a/core/modules/language/src/Form/ContentLanguageSettingsForm.php
+++ b/core/modules/language/src/Form/ContentLanguageSettingsForm.php
@@ -11,6 +11,8 @@

 /**
  * Configure the content language settings for this site.
+ *
+ * @internal
  */
 class ContentLanguageSettingsForm extends FormBase {

diff --git a/core/modules/language/src/Form/LanguageAddForm.php b/core/modules/language/src/Form/LanguageAddForm.php
index 5b9f15c..1248407 100644
--- a/core/modules/language/src/Form/LanguageAddForm.php
+++ b/core/modules/language/src/Form/LanguageAddForm.php
@@ -9,6 +9,8 @@

 /**
  * Controller for language addition forms.
+ *
+ * @internal
  */
 class LanguageAddForm extends LanguageFormBase {

diff --git a/core/modules/language/src/Form/LanguageDeleteForm.php b/core/modules/language/src/Form/LanguageDeleteForm.php
index 6113c1f..6d4107a 100644
--- a/core/modules/language/src/Form/LanguageDeleteForm.php
+++ b/core/modules/language/src/Form/LanguageDeleteForm.php
@@ -6,6 +6,8 @@

 /**
  * Defines a confirmation form for deleting a language entity.
+ *
+ * @internal
  */
 class LanguageDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/language/src/Form/LanguageEditForm.php b/core/modules/language/src/Form/LanguageEditForm.php
index 234994d..7930fbd 100644
--- a/core/modules/language/src/Form/LanguageEditForm.php
+++ b/core/modules/language/src/Form/LanguageEditForm.php
@@ -6,6 +6,8 @@

 /**
  * Controller for language edit forms.
+ *
+ * @internal
  */
 class LanguageEditForm extends LanguageFormBase {

diff --git a/core/modules/language/src/Form/LanguageFormBase.php b/core/modules/language/src/Form/LanguageFormBase.php
index 8c8f5fa..b8ba3b4 100644
--- a/core/modules/language/src/Form/LanguageFormBase.php
+++ b/core/modules/language/src/Form/LanguageFormBase.php
@@ -11,6 +11,8 @@

 /**
  * Base form for language add and edit forms.
+ *
+ * @internal
  */
 abstract class LanguageFormBase extends EntityForm {

diff --git a/core/modules/language/src/Form/NegotiationBrowserDeleteForm.php b/core/modules/language/src/Form/NegotiationBrowserDeleteForm.php
index 1a40946..629fd08 100644
--- a/core/modules/language/src/Form/NegotiationBrowserDeleteForm.php
+++ b/core/modules/language/src/Form/NegotiationBrowserDeleteForm.php
@@ -9,6 +9,8 @@

 /**
  * Defines a confirmation form for deleting a browser language negotiation mapping.
+ *
+ * @internal
  */
 class NegotiationBrowserDeleteForm extends ConfirmFormBase {
   use ConfigFormBaseTrait;
diff --git a/core/modules/language/src/Form/NegotiationBrowserForm.php b/core/modules/language/src/Form/NegotiationBrowserForm.php
index 5535fe0..1e44afe 100644
--- a/core/modules/language/src/Form/NegotiationBrowserForm.php
+++ b/core/modules/language/src/Form/NegotiationBrowserForm.php
@@ -11,6 +11,8 @@

 /**
  * Configure the browser language negotiation method for this site.
+ *
+ * @internal
  */
 class NegotiationBrowserForm extends ConfigFormBase {

diff --git a/core/modules/language/src/Form/NegotiationConfigureForm.php b/core/modules/language/src/Form/NegotiationConfigureForm.php
index c1333e6..e029134 100644
--- a/core/modules/language/src/Form/NegotiationConfigureForm.php
+++ b/core/modules/language/src/Form/NegotiationConfigureForm.php
@@ -17,6 +17,8 @@

 /**
  * Configure the selected language negotiation method for this site.
+ *
+ * @internal
  */
 class NegotiationConfigureForm extends ConfigFormBase {

diff --git a/core/modules/language/src/Form/NegotiationSelectedForm.php b/core/modules/language/src/Form/NegotiationSelectedForm.php
index d4f1191..680dddf 100644
--- a/core/modules/language/src/Form/NegotiationSelectedForm.php
+++ b/core/modules/language/src/Form/NegotiationSelectedForm.php
@@ -8,6 +8,8 @@

 /**
  * Configure the selected language negotiation method for this site.
+ *
+ * @internal
  */
 class NegotiationSelectedForm extends ConfigFormBase {

diff --git a/core/modules/language/src/Form/NegotiationSessionForm.php b/core/modules/language/src/Form/NegotiationSessionForm.php
index b7ec450..f2541c1 100644
--- a/core/modules/language/src/Form/NegotiationSessionForm.php
+++ b/core/modules/language/src/Form/NegotiationSessionForm.php
@@ -7,6 +7,8 @@

 /**
  * Configure the session language negotiation method for this site.
+ *
+ * @internal
  */
 class NegotiationSessionForm extends ConfigFormBase {

diff --git a/core/modules/language/src/Form/NegotiationUrlForm.php b/core/modules/language/src/Form/NegotiationUrlForm.php
index 6f44f60..89ba536 100644
--- a/core/modules/language/src/Form/NegotiationUrlForm.php
+++ b/core/modules/language/src/Form/NegotiationUrlForm.php
@@ -12,6 +12,8 @@

 /**
  * Configure the URL language negotiation method for this site.
+ *
+ * @internal
  */
 class NegotiationUrlForm extends ConfigFormBase {

diff --git a/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElement.php b/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElement.php
index 4021667..33416df 100644
--- a/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElement.php
+++ b/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElement.php
@@ -8,6 +8,8 @@

 /**
  * A form containing a language configuration element.
+ *
+ * @internal
  */
 class LanguageConfigurationElement extends FormBase {

diff --git a/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElementTest.php b/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElementTest.php
index f0fe8c5..f0eb60e 100644
--- a/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElementTest.php
+++ b/core/modules/language/tests/language_elements_test/src/Form/LanguageConfigurationElementTest.php
@@ -7,6 +7,8 @@

 /**
  * A form containing a language select element.
+ *
+ * @internal
  */
 class LanguageConfigurationElementTest extends FormBase {

diff --git a/core/modules/locale/src/Form/ExportForm.php b/core/modules/locale/src/Form/ExportForm.php
index 7c6f932..fc5b05d 100644
--- a/core/modules/locale/src/Form/ExportForm.php
+++ b/core/modules/locale/src/Form/ExportForm.php
@@ -14,6 +14,8 @@

 /**
  * Form for the Gettext translation files export form.
+ *
+ * @internal
  */
 class ExportForm extends FormBase {

diff --git a/core/modules/locale/src/Form/ImportForm.php b/core/modules/locale/src/Form/ImportForm.php
index f2bd45b..0cc6749 100644
--- a/core/modules/locale/src/Form/ImportForm.php
+++ b/core/modules/locale/src/Form/ImportForm.php
@@ -11,6 +11,8 @@

 /**
  * Form constructor for the translation import screen.
+ *
+ * @internal
  */
 class ImportForm extends FormBase {

diff --git a/core/modules/locale/src/Form/LocaleSettingsForm.php b/core/modules/locale/src/Form/LocaleSettingsForm.php
index e722cfb..78945eb 100644
--- a/core/modules/locale/src/Form/LocaleSettingsForm.php
+++ b/core/modules/locale/src/Form/LocaleSettingsForm.php
@@ -7,6 +7,8 @@

 /**
  * Configure locale settings for this site.
+ *
+ * @internal
  */
 class LocaleSettingsForm extends ConfigFormBase {

diff --git a/core/modules/locale/src/Form/TranslateEditForm.php b/core/modules/locale/src/Form/TranslateEditForm.php
index d629009..79656f2 100644
--- a/core/modules/locale/src/Form/TranslateEditForm.php
+++ b/core/modules/locale/src/Form/TranslateEditForm.php
@@ -8,6 +8,8 @@

 /**
  * Defines a translation edit form.
+ *
+ * @internal
  */
 class TranslateEditForm extends TranslateFormBase {

diff --git a/core/modules/locale/src/Form/TranslateFilterForm.php b/core/modules/locale/src/Form/TranslateFilterForm.php
index aeef26f..cfa3b69 100644
--- a/core/modules/locale/src/Form/TranslateFilterForm.php
+++ b/core/modules/locale/src/Form/TranslateFilterForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a filtered translation edit form.
+ *
+ * @internal
  */
 class TranslateFilterForm extends TranslateFormBase {

diff --git a/core/modules/locale/src/Form/TranslateFormBase.php b/core/modules/locale/src/Form/TranslateFormBase.php
index 9a7ad8b..3e7e8e6 100644
--- a/core/modules/locale/src/Form/TranslateFormBase.php
+++ b/core/modules/locale/src/Form/TranslateFormBase.php
@@ -12,6 +12,8 @@
  * Defines the locale user interface translation form base.
  *
  * Provides methods for searching and filtering strings.
+ *
+ * @internal
  */
 abstract class TranslateFormBase extends FormBase {

diff --git a/core/modules/locale/src/Form/TranslationStatusForm.php b/core/modules/locale/src/Form/TranslationStatusForm.php
index cbf4d4a..418fc78 100644
--- a/core/modules/locale/src/Form/TranslationStatusForm.php
+++ b/core/modules/locale/src/Form/TranslationStatusForm.php
@@ -10,6 +10,8 @@

 /**
  * Provides a translation status form.
+ *
+ * @internal
  */
 class TranslationStatusForm extends FormBase {

diff --git a/core/modules/menu_link_content/src/Form/MenuLinkContentDeleteForm.php b/core/modules/menu_link_content/src/Form/MenuLinkContentDeleteForm.php
index 2b780c9..e9f9538 100644
--- a/core/modules/menu_link_content/src/Form/MenuLinkContentDeleteForm.php
+++ b/core/modules/menu_link_content/src/Form/MenuLinkContentDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a delete form for content menu links.
+ *
+ * @internal
  */
 class MenuLinkContentDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php b/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php
index 4bdd6b9..7175c1b 100644
--- a/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php
+++ b/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php
@@ -14,6 +14,8 @@

 /**
  * Provides a form to add/update content menu links.
+ *
+ * @internal
  */
 class MenuLinkContentForm extends ContentEntityForm {

diff --git a/core/modules/menu_ui/src/Form/MenuDeleteForm.php b/core/modules/menu_ui/src/Form/MenuDeleteForm.php
index 1cebd90..1b057a6 100644
--- a/core/modules/menu_ui/src/Form/MenuDeleteForm.php
+++ b/core/modules/menu_ui/src/Form/MenuDeleteForm.php
@@ -10,6 +10,8 @@

 /**
  * Defines a confirmation form for deletion of a custom menu.
+ *
+ * @internal
  */
 class MenuDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/menu_ui/src/Form/MenuLinkEditForm.php b/core/modules/menu_ui/src/Form/MenuLinkEditForm.php
index 2dbd6a5..6cb50da 100644
--- a/core/modules/menu_ui/src/Form/MenuLinkEditForm.php
+++ b/core/modules/menu_ui/src/Form/MenuLinkEditForm.php
@@ -13,6 +13,8 @@
  *
  * The menu link plugin defines which class defines the corresponding form.
  *
+ * @internal
+ *
  * @see \Drupal\Core\Menu\MenuLinkInterface::getFormClass()
  */
 class MenuLinkEditForm extends FormBase {
diff --git a/core/modules/menu_ui/src/Form/MenuLinkResetForm.php b/core/modules/menu_ui/src/Form/MenuLinkResetForm.php
index e37b16b..de9dccb 100644
--- a/core/modules/menu_ui/src/Form/MenuLinkResetForm.php
+++ b/core/modules/menu_ui/src/Form/MenuLinkResetForm.php
@@ -12,6 +12,8 @@

 /**
  * Defines a confirmation form for resetting a single modified menu link.
+ *
+ * @internal
  */
 class MenuLinkResetForm extends ConfirmFormBase {

diff --git a/core/modules/menu_ui/src/MenuForm.php b/core/modules/menu_ui/src/MenuForm.php
index 0bee996..fe9718e 100644
--- a/core/modules/menu_ui/src/MenuForm.php
+++ b/core/modules/menu_ui/src/MenuForm.php
@@ -19,6 +19,8 @@

 /**
  * Base form for menu edit forms.
+ *
+ * @internal
  */
 class MenuForm extends EntityForm {

diff --git a/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
index d64a0d6..bed1e31 100644
--- a/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
+++ b/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeForm.php
@@ -15,6 +15,8 @@

 /**
  * Defines a multi-step form for performing direct site upgrades.
+ *
+ * @internal
  */
 class MigrateUpgradeForm extends ConfirmFormBase {

diff --git a/core/modules/node/src/Form/DeleteMultiple.php b/core/modules/node/src/Form/DeleteMultiple.php
index 91d8ad4..8bc8f06 100644
--- a/core/modules/node/src/Form/DeleteMultiple.php
+++ b/core/modules/node/src/Form/DeleteMultiple.php
@@ -12,6 +12,8 @@

 /**
  * Provides a node deletion confirmation form.
+ *
+ * @internal
  */
 class DeleteMultiple extends ConfirmFormBase {

diff --git a/core/modules/node/src/Form/NodeDeleteForm.php b/core/modules/node/src/Form/NodeDeleteForm.php
index da8c202..3f47a0c 100644
--- a/core/modules/node/src/Form/NodeDeleteForm.php
+++ b/core/modules/node/src/Form/NodeDeleteForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a form for deleting a node.
+ *
+ * @internal
  */
 class NodeDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/node/src/Form/NodePreviewForm.php b/core/modules/node/src/Form/NodePreviewForm.php
index 8b6125b..b06a657 100644
--- a/core/modules/node/src/Form/NodePreviewForm.php
+++ b/core/modules/node/src/Form/NodePreviewForm.php
@@ -12,6 +12,8 @@

 /**
  * Contains a form for switching the view mode of a node during preview.
+ *
+ * @internal
  */
 class NodePreviewForm extends FormBase {

diff --git a/core/modules/node/src/Form/NodeRevisionDeleteForm.php b/core/modules/node/src/Form/NodeRevisionDeleteForm.php
index 86e5b59..47e7799 100644
--- a/core/modules/node/src/Form/NodeRevisionDeleteForm.php
+++ b/core/modules/node/src/Form/NodeRevisionDeleteForm.php
@@ -11,6 +11,8 @@

 /**
  * Provides a form for reverting a node revision.
+ *
+ * @internal
  */
 class NodeRevisionDeleteForm extends ConfirmFormBase {

diff --git a/core/modules/node/src/Form/NodeRevisionRevertForm.php b/core/modules/node/src/Form/NodeRevisionRevertForm.php
index 8137c3f..fc6fe02 100644
--- a/core/modules/node/src/Form/NodeRevisionRevertForm.php
+++ b/core/modules/node/src/Form/NodeRevisionRevertForm.php
@@ -13,6 +13,8 @@

 /**
  * Provides a form for reverting a node revision.
+ *
+ * @internal
  */
 class NodeRevisionRevertForm extends ConfirmFormBase {

diff --git a/core/modules/node/src/Form/NodeRevisionRevertTranslationForm.php b/core/modules/node/src/Form/NodeRevisionRevertTranslationForm.php
index d5da697..0c68d8b 100644
--- a/core/modules/node/src/Form/NodeRevisionRevertTranslationForm.php
+++ b/core/modules/node/src/Form/NodeRevisionRevertTranslationForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a form for reverting a node revision for a single translation.
+ *
+ * @internal
  */
 class NodeRevisionRevertTranslationForm extends NodeRevisionRevertForm {

diff --git a/core/modules/node/src/Form/NodeTypeDeleteConfirm.php b/core/modules/node/src/Form/NodeTypeDeleteConfirm.php
index e4bea83..8234fcd 100644
--- a/core/modules/node/src/Form/NodeTypeDeleteConfirm.php
+++ b/core/modules/node/src/Form/NodeTypeDeleteConfirm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a form for content type deletion.
+ *
+ * @internal
  */
 class NodeTypeDeleteConfirm extends EntityDeleteForm {

diff --git a/core/modules/node/src/Form/RebuildPermissionsForm.php b/core/modules/node/src/Form/RebuildPermissionsForm.php
index b895c4c..7ca89e7 100644
--- a/core/modules/node/src/Form/RebuildPermissionsForm.php
+++ b/core/modules/node/src/Form/RebuildPermissionsForm.php
@@ -6,6 +6,12 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Url;

+/**
+ * Form for rebuilding permissions.
+ *
+ * @internal
+ */
+
 class RebuildPermissionsForm extends ConfirmFormBase {

   /**
diff --git a/core/modules/node/src/NodeForm.php b/core/modules/node/src/NodeForm.php
index 203c2e6..7ffef55 100644
--- a/core/modules/node/src/NodeForm.php
+++ b/core/modules/node/src/NodeForm.php
@@ -12,6 +12,8 @@

 /**
  * Form handler for the node edit forms.
+ *
+ * @internal
  */
 class NodeForm extends ContentEntityForm {

diff --git a/core/modules/node/src/NodeTypeForm.php b/core/modules/node/src/NodeTypeForm.php
index abef502..9eec40c 100644
--- a/core/modules/node/src/NodeTypeForm.php
+++ b/core/modules/node/src/NodeTypeForm.php
@@ -11,6 +11,8 @@

 /**
  * Form handler for node type forms.
+ *
+ * @internal
  */
 class NodeTypeForm extends BundleEntityFormBase {

diff --git a/core/modules/page_cache/tests/modules/src/Form/TestForm.php b/core/modules/page_cache/tests/modules/src/Form/TestForm.php
index 7b60343..e9f4a4f 100644
--- a/core/modules/page_cache/tests/modules/src/Form/TestForm.php
+++ b/core/modules/page_cache/tests/modules/src/Form/TestForm.php
@@ -5,6 +5,11 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;

+/**
+ * A form to test page cache.
+ *
+ * @internal
+ */
 class TestForm extends FormBase {

   /**
diff --git a/core/modules/path/src/Form/AddForm.php b/core/modules/path/src/Form/AddForm.php
index 8f8d4f6..59db6f9 100644
--- a/core/modules/path/src/Form/AddForm.php
+++ b/core/modules/path/src/Form/AddForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides the path add form.
+ *
+ * @internal
  */
 class AddForm extends PathFormBase {

diff --git a/core/modules/path/src/Form/DeleteForm.php b/core/modules/path/src/Form/DeleteForm.php
index b28fdc0..171bd7f 100644
--- a/core/modules/path/src/Form/DeleteForm.php
+++ b/core/modules/path/src/Form/DeleteForm.php
@@ -10,6 +10,8 @@

 /**
  * Builds the form to delete a path alias.
+ *
+ * @internal
  */
 class DeleteForm extends ConfirmFormBase {

diff --git a/core/modules/path/src/Form/EditForm.php b/core/modules/path/src/Form/EditForm.php
index 7d4a369..9638b57 100644
--- a/core/modules/path/src/Form/EditForm.php
+++ b/core/modules/path/src/Form/EditForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the path edit form.
+ *
+ * @internal
  */
 class EditForm extends PathFormBase {

diff --git a/core/modules/path/src/Form/PathFilterForm.php b/core/modules/path/src/Form/PathFilterForm.php
index f782906..98bd952 100644
--- a/core/modules/path/src/Form/PathFilterForm.php
+++ b/core/modules/path/src/Form/PathFilterForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the path admin overview filter form.
+ *
+ * @internal
  */
 class PathFilterForm extends FormBase {

diff --git a/core/modules/path/src/Form/PathFormBase.php b/core/modules/path/src/Form/PathFormBase.php
index 884d24f..16ec532 100644
--- a/core/modules/path/src/Form/PathFormBase.php
+++ b/core/modules/path/src/Form/PathFormBase.php
@@ -13,6 +13,8 @@

 /**
  * Provides a base class for path add/edit forms.
+ *
+ * @internal
  */
 abstract class PathFormBase extends FormBase {

diff --git a/core/modules/quickedit/src/Form/QuickEditFieldForm.php b/core/modules/quickedit/src/Form/QuickEditFieldForm.php
index ba2dac3..31cc004 100644
--- a/core/modules/quickedit/src/Form/QuickEditFieldForm.php
+++ b/core/modules/quickedit/src/Form/QuickEditFieldForm.php
@@ -16,6 +16,8 @@

 /**
  * Builds and process a form for editing a single entity field.
+ *
+ * @internal
  */
 class QuickEditFieldForm extends FormBase {

diff --git a/core/modules/responsive_image/src/ResponsiveImageStyleForm.php b/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
index 8ad0e6a..4240473 100644
--- a/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
+++ b/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
@@ -9,6 +9,8 @@

 /**
  * Form controller for the responsive image edit/add forms.
+ *
+ * @internal
  */
 class ResponsiveImageStyleForm extends EntityForm {

diff --git a/core/modules/search/src/Form/ReindexConfirm.php b/core/modules/search/src/Form/ReindexConfirm.php
index 9cd4a15..2a30cb5 100644
--- a/core/modules/search/src/Form/ReindexConfirm.php
+++ b/core/modules/search/src/Form/ReindexConfirm.php
@@ -8,6 +8,8 @@

 /**
  * Provides the search reindex confirmation form.
+ *
+ * @internal
  */
 class ReindexConfirm extends ConfirmFormBase {

diff --git a/core/modules/search/src/Form/SearchBlockForm.php b/core/modules/search/src/Form/SearchBlockForm.php
index 7a9405f..612f8f6 100644
--- a/core/modules/search/src/Form/SearchBlockForm.php
+++ b/core/modules/search/src/Form/SearchBlockForm.php
@@ -11,6 +11,8 @@

 /**
  * Builds the search form for the search block.
+ *
+ * @internal
  */
 class SearchBlockForm extends FormBase {

diff --git a/core/modules/search/src/Form/SearchPageAddForm.php b/core/modules/search/src/Form/SearchPageAddForm.php
index d5bc785..6f5c142 100644
--- a/core/modules/search/src/Form/SearchPageAddForm.php
+++ b/core/modules/search/src/Form/SearchPageAddForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a form for adding a search page.
+ *
+ * @internal
  */
 class SearchPageAddForm extends SearchPageFormBase {

diff --git a/core/modules/search/src/Form/SearchPageEditForm.php b/core/modules/search/src/Form/SearchPageEditForm.php
index 9d082eb..afbcfbc 100644
--- a/core/modules/search/src/Form/SearchPageEditForm.php
+++ b/core/modules/search/src/Form/SearchPageEditForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a form for editing a search page.
+ *
+ * @internal
  */
 class SearchPageEditForm extends SearchPageFormBase {

diff --git a/core/modules/search/src/Form/SearchPageForm.php b/core/modules/search/src/Form/SearchPageForm.php
index e46195b..0d8a34e 100644
--- a/core/modules/search/src/Form/SearchPageForm.php
+++ b/core/modules/search/src/Form/SearchPageForm.php
@@ -15,6 +15,8 @@
  * submit, making sure to redirect with a GET parameter of 'keys' included, to
  * trigger the search being processed by the controller, and adding in any
  * additional query parameters they need to execute search.
+ *
+ * @internal
  */
 class SearchPageForm extends FormBase {

diff --git a/core/modules/search/src/Form/SearchPageFormBase.php b/core/modules/search/src/Form/SearchPageFormBase.php
index 1638f90..ac2bdcf 100644
--- a/core/modules/search/src/Form/SearchPageFormBase.php
+++ b/core/modules/search/src/Form/SearchPageFormBase.php
@@ -10,6 +10,8 @@

 /**
  * Provides a base form for search pages.
+ *
+ * @internal
  */
 abstract class SearchPageFormBase extends EntityForm {

diff --git a/core/modules/search/tests/modules/search_embedded_form/src/Form/SearchEmbeddedForm.php b/core/modules/search/tests/modules/search_embedded_form/src/Form/SearchEmbeddedForm.php
index 64d9418..b1e26ca 100644
--- a/core/modules/search/tests/modules/search_embedded_form/src/Form/SearchEmbeddedForm.php
+++ b/core/modules/search/tests/modules/search_embedded_form/src/Form/SearchEmbeddedForm.php
@@ -7,6 +7,8 @@

 /**
  * Form controller for search_embedded_form form.
+ *
+ * @internal
  */
 class SearchEmbeddedForm extends FormBase {

diff --git a/core/modules/shortcut/src/Form/SetCustomize.php b/core/modules/shortcut/src/Form/SetCustomize.php
index 6c97577..20094aa 100644
--- a/core/modules/shortcut/src/Form/SetCustomize.php
+++ b/core/modules/shortcut/src/Form/SetCustomize.php
@@ -8,6 +8,8 @@

 /**
  * Builds the shortcut set customize form.
+ *
+ * @internal
  */
 class SetCustomize extends EntityForm {

diff --git a/core/modules/shortcut/src/Form/ShortcutDeleteForm.php b/core/modules/shortcut/src/Form/ShortcutDeleteForm.php
index fcabeec..0e6c32c 100644
--- a/core/modules/shortcut/src/Form/ShortcutDeleteForm.php
+++ b/core/modules/shortcut/src/Form/ShortcutDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds the shortcut link deletion form.
+ *
+ * @internal
  */
 class ShortcutDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/shortcut/src/Form/ShortcutSetDeleteForm.php b/core/modules/shortcut/src/Form/ShortcutSetDeleteForm.php
index c383627..b14e4e3 100644
--- a/core/modules/shortcut/src/Form/ShortcutSetDeleteForm.php
+++ b/core/modules/shortcut/src/Form/ShortcutSetDeleteForm.php
@@ -10,6 +10,8 @@

 /**
  * Builds the shortcut set deletion form.
+ *
+ * @internal
  */
 class ShortcutSetDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/shortcut/src/Form/SwitchShortcutSet.php b/core/modules/shortcut/src/Form/SwitchShortcutSet.php
index 649cef7..726af17 100644
--- a/core/modules/shortcut/src/Form/SwitchShortcutSet.php
+++ b/core/modules/shortcut/src/Form/SwitchShortcutSet.php
@@ -11,6 +11,8 @@

 /**
  * Builds the shortcut set switch form.
+ *
+ * @internal
  */
 class SwitchShortcutSet extends FormBase {

diff --git a/core/modules/shortcut/src/ShortcutForm.php b/core/modules/shortcut/src/ShortcutForm.php
index bfe3133..fa62cdb 100644
--- a/core/modules/shortcut/src/ShortcutForm.php
+++ b/core/modules/shortcut/src/ShortcutForm.php
@@ -7,6 +7,8 @@

 /**
  * Form handler for the shortcut entity forms.
+ *
+ * @internal
  */
 class ShortcutForm extends ContentEntityForm {

diff --git a/core/modules/shortcut/src/ShortcutSetForm.php b/core/modules/shortcut/src/ShortcutSetForm.php
index 721d251..3c8f4a7 100644
--- a/core/modules/shortcut/src/ShortcutSetForm.php
+++ b/core/modules/shortcut/src/ShortcutSetForm.php
@@ -7,6 +7,8 @@

 /**
  * Form handler for the shortcut set entity edit forms.
+ *
+ * @internal
  */
 class ShortcutSetForm extends BundleEntityFormBase {

diff --git a/core/modules/simpletest/src/Form/SimpletestResultsForm.php b/core/modules/simpletest/src/Form/SimpletestResultsForm.php
index 090ae02..ed085e6 100644
--- a/core/modules/simpletest/src/Form/SimpletestResultsForm.php
+++ b/core/modules/simpletest/src/Form/SimpletestResultsForm.php
@@ -17,6 +17,8 @@
  * Note that the UI strings are not translated because this form is also used
  * from run-tests.sh.
  *
+ * @internal
+ *
  * @see simpletest_script_open_browser()
  * @see run-tests.sh
  */
diff --git a/core/modules/simpletest/src/Form/SimpletestSettingsForm.php b/core/modules/simpletest/src/Form/SimpletestSettingsForm.php
index d1ee436..20d2425 100644
--- a/core/modules/simpletest/src/Form/SimpletestSettingsForm.php
+++ b/core/modules/simpletest/src/Form/SimpletestSettingsForm.php
@@ -7,6 +7,8 @@

 /**
  * Configure simpletest settings for this site.
+ *
+ * @internal
  */
 class SimpletestSettingsForm extends ConfigFormBase {

diff --git a/core/modules/simpletest/src/Form/SimpletestTestForm.php b/core/modules/simpletest/src/Form/SimpletestTestForm.php
index 1bf43ce..0b704f9 100644
--- a/core/modules/simpletest/src/Form/SimpletestTestForm.php
+++ b/core/modules/simpletest/src/Form/SimpletestTestForm.php
@@ -10,6 +10,8 @@

 /**
  * List tests arranged in groups that can be selected and run.
+ *
+ * @internal
  */
 class SimpletestTestForm extends FormBase {

diff --git a/core/modules/system/src/Form/DateFormatAddForm.php b/core/modules/system/src/Form/DateFormatAddForm.php
index 957f967..e30fbfc 100644
--- a/core/modules/system/src/Form/DateFormatAddForm.php
+++ b/core/modules/system/src/Form/DateFormatAddForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a form for adding a date format.
+ *
+ * @internal
  */
 class DateFormatAddForm extends DateFormatFormBase {

diff --git a/core/modules/system/src/Form/DateFormatDeleteForm.php b/core/modules/system/src/Form/DateFormatDeleteForm.php
index 901c34b..b1f05eb 100644
--- a/core/modules/system/src/Form/DateFormatDeleteForm.php
+++ b/core/modules/system/src/Form/DateFormatDeleteForm.php
@@ -8,6 +8,8 @@

 /**
  * Builds a form to delete a date format.
+ *
+ * @internal
  */
 class DateFormatDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/system/src/Form/DateFormatEditForm.php b/core/modules/system/src/Form/DateFormatEditForm.php
index c63c0d7..d6ad88e 100644
--- a/core/modules/system/src/Form/DateFormatEditForm.php
+++ b/core/modules/system/src/Form/DateFormatEditForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a form for editing a date format.
+ *
+ * @internal
  */
 class DateFormatEditForm extends DateFormatFormBase {

diff --git a/core/modules/system/src/Form/DateFormatFormBase.php b/core/modules/system/src/Form/DateFormatFormBase.php
index ed6714f..b1c71cd 100644
--- a/core/modules/system/src/Form/DateFormatFormBase.php
+++ b/core/modules/system/src/Form/DateFormatFormBase.php
@@ -12,6 +12,8 @@

 /**
  * Provides a base form for date formats.
+ *
+ * @internal
  */
 abstract class DateFormatFormBase extends EntityForm {

diff --git a/core/modules/system/src/Form/FileSystemForm.php b/core/modules/system/src/Form/FileSystemForm.php
index ff0b792..958d675 100644
--- a/core/modules/system/src/Form/FileSystemForm.php
+++ b/core/modules/system/src/Form/FileSystemForm.php
@@ -14,6 +14,8 @@

 /**
  * Configure file system settings for this site.
+ *
+ * @internal
  */
 class FileSystemForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/ImageToolkitForm.php b/core/modules/system/src/Form/ImageToolkitForm.php
index 0e70b47..8684c77 100644
--- a/core/modules/system/src/Form/ImageToolkitForm.php
+++ b/core/modules/system/src/Form/ImageToolkitForm.php
@@ -10,6 +10,8 @@

 /**
  * Configures image toolkit settings for this site.
+ *
+ * @internal
  */
 class ImageToolkitForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/LoggingForm.php b/core/modules/system/src/Form/LoggingForm.php
index a305a4f..b6446df 100644
--- a/core/modules/system/src/Form/LoggingForm.php
+++ b/core/modules/system/src/Form/LoggingForm.php
@@ -7,6 +7,8 @@

 /**
  * Configure logging settings for this site.
+ *
+ * @internal
  */
 class LoggingForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/ModulesListConfirmForm.php b/core/modules/system/src/Form/ModulesListConfirmForm.php
index 5002660..912a432 100644
--- a/core/modules/system/src/Form/ModulesListConfirmForm.php
+++ b/core/modules/system/src/Form/ModulesListConfirmForm.php
@@ -14,6 +14,8 @@

 /**
  * Builds a confirmation form for enabling modules with dependencies.
+ *
+ * @internal
  */
 class ModulesListConfirmForm extends ConfirmFormBase {

diff --git a/core/modules/system/src/Form/ModulesListExperimentalConfirmForm.php b/core/modules/system/src/Form/ModulesListExperimentalConfirmForm.php
index 7488544..5586ce7 100644
--- a/core/modules/system/src/Form/ModulesListExperimentalConfirmForm.php
+++ b/core/modules/system/src/Form/ModulesListExperimentalConfirmForm.php
@@ -4,6 +4,8 @@

 /**
  * Builds a confirmation form for enabling experimental modules.
+ *
+ * @internal
  */
 class ModulesListExperimentalConfirmForm extends ModulesListConfirmForm {

diff --git a/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
index 28ff7ef..43969d4 100644
--- a/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -25,6 +25,8 @@
  * each module's name, description, and information about which modules it
  * requires. See \Drupal\Core\Extension\InfoParser for info on module.info.yml
  * descriptors.
+ *
+ * @internal
  */
 class ModulesListForm extends FormBase {

diff --git a/core/modules/system/src/Form/ModulesUninstallConfirmForm.php b/core/modules/system/src/Form/ModulesUninstallConfirmForm.php
index c72f240..f55f0d6 100644
--- a/core/modules/system/src/Form/ModulesUninstallConfirmForm.php
+++ b/core/modules/system/src/Form/ModulesUninstallConfirmForm.php
@@ -14,6 +14,8 @@

 /**
  * Builds a confirmation form to uninstall selected modules.
+ *
+ * @internal
  */
 class ModulesUninstallConfirmForm extends ConfirmFormBase {
   use ConfigDependencyDeleteFormTrait;
diff --git a/core/modules/system/src/Form/ModulesUninstallForm.php b/core/modules/system/src/Form/ModulesUninstallForm.php
index 80348c5..7949067 100644
--- a/core/modules/system/src/Form/ModulesUninstallForm.php
+++ b/core/modules/system/src/Form/ModulesUninstallForm.php
@@ -11,6 +11,8 @@

 /**
  * Provides a form for uninstalling modules.
+ *
+ * @internal
  */
 class ModulesUninstallForm extends FormBase {

diff --git a/core/modules/system/src/Form/PerformanceForm.php b/core/modules/system/src/Form/PerformanceForm.php
index a2e8592..9fb5912 100644
--- a/core/modules/system/src/Form/PerformanceForm.php
+++ b/core/modules/system/src/Form/PerformanceForm.php
@@ -12,6 +12,8 @@

 /**
  * Configure performance settings for this site.
+ *
+ * @internal
  */
 class PerformanceForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/PrepareModulesEntityUninstallForm.php b/core/modules/system/src/Form/PrepareModulesEntityUninstallForm.php
index 858364f..fb73b99 100644
--- a/core/modules/system/src/Form/PrepareModulesEntityUninstallForm.php
+++ b/core/modules/system/src/Form/PrepareModulesEntityUninstallForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a form removing module content entities data before uninstallation.
+ *
+ * @internal
  */
 class PrepareModulesEntityUninstallForm extends ConfirmFormBase {

diff --git a/core/modules/system/src/Form/RegionalForm.php b/core/modules/system/src/Form/RegionalForm.php
index c365fc0..2d9ea33 100644
--- a/core/modules/system/src/Form/RegionalForm.php
+++ b/core/modules/system/src/Form/RegionalForm.php
@@ -10,6 +10,8 @@

 /**
  * Configure regional settings for this site.
+ *
+ * @internal
  */
 class RegionalForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/RssFeedsForm.php b/core/modules/system/src/Form/RssFeedsForm.php
index 986ff11..d7508e6 100644
--- a/core/modules/system/src/Form/RssFeedsForm.php
+++ b/core/modules/system/src/Form/RssFeedsForm.php
@@ -6,7 +6,9 @@
 use Drupal\Core\Form\FormStateInterface;

 /**
- * Configure RSS settings for this site.
+ * Configure RSS settings for this site
+ *
+ * @internal
  */
 class RssFeedsForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/SiteInformationForm.php b/core/modules/system/src/Form/SiteInformationForm.php
index 7173ebe..db44dd7 100644
--- a/core/modules/system/src/Form/SiteInformationForm.php
+++ b/core/modules/system/src/Form/SiteInformationForm.php
@@ -12,6 +12,8 @@

 /**
  * Configure site information settings for this site.
+ *
+ * @internal
  */
 class SiteInformationForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/SiteMaintenanceModeForm.php b/core/modules/system/src/Form/SiteMaintenanceModeForm.php
index fb509aa..58b1f1a 100644
--- a/core/modules/system/src/Form/SiteMaintenanceModeForm.php
+++ b/core/modules/system/src/Form/SiteMaintenanceModeForm.php
@@ -11,6 +11,8 @@

 /**
  * Configure maintenance settings for this site.
+ *
+ * @internal
  */
 class SiteMaintenanceModeForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/ThemeAdminForm.php b/core/modules/system/src/Form/ThemeAdminForm.php
index e8d17ed..1c85a78 100644
--- a/core/modules/system/src/Form/ThemeAdminForm.php
+++ b/core/modules/system/src/Form/ThemeAdminForm.php
@@ -7,6 +7,8 @@

 /**
  * Form to select the administration theme.
+ *
+ * @internal
  */
 class ThemeAdminForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/ThemeSettingsForm.php b/core/modules/system/src/Form/ThemeSettingsForm.php
index f5cfb09..ffbafa7 100644
--- a/core/modules/system/src/Form/ThemeSettingsForm.php
+++ b/core/modules/system/src/Form/ThemeSettingsForm.php
@@ -16,6 +16,8 @@

 /**
  * Displays theme configuration for entire site and individual themes.
+ *
+ * @internal
  */
 class ThemeSettingsForm extends ConfigFormBase {

diff --git a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCommandsForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCommandsForm.php
index e3c09af..c7861e6 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCommandsForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCommandsForm.php
@@ -7,6 +7,8 @@

 /**
  * Form constructor for the Ajax Command display form.
+ *
+ * @internal
  */
 class AjaxFormsTestCommandsForm extends FormBase {

diff --git a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestLazyLoadForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestLazyLoadForm.php
index 852cf44..7dddf87 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestLazyLoadForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestLazyLoadForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder: Builds a form that triggers a simple AJAX callback.
+ *
+ * @internal
  */
 class AjaxFormsTestLazyLoadForm extends FormBase {

diff --git a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestSimpleForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestSimpleForm.php
index f69a123..2d4dc19 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestSimpleForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestSimpleForm.php
@@ -8,6 +8,8 @@

 /**
  * Form builder: Builds a form that triggers a simple AJAX callback.
+ *
+ * @internal
  */
 class AjaxFormsTestSimpleForm extends FormBase {

diff --git a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestValidationForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestValidationForm.php
index fb30194..d908e38 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestValidationForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestValidationForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder: Builds a form that triggers a simple AJAX callback.
+ *
+ * @internal
  */
 class AjaxFormsTestValidationForm extends FormBase {

diff --git a/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestDialogForm.php b/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestDialogForm.php
index 5f11b6b..daedcf1 100644
--- a/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestDialogForm.php
+++ b/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestDialogForm.php
@@ -11,6 +11,8 @@

 /**
  * Dummy form for testing DialogRenderer with _form routes.
+ *
+ * @internal
  */
 class AjaxTestDialogForm extends FormBase {

diff --git a/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestForm.php b/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestForm.php
index ea431ef..76dd497 100644
--- a/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestForm.php
+++ b/core/modules/system/tests/modules/ajax_test/src/Form/AjaxTestForm.php
@@ -7,6 +7,8 @@

 /**
  * Dummy form for testing DialogRenderer with _form routes.
+ *
+ * @internal
  */
 class AjaxTestForm extends FormBase {

diff --git a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestChainedForm.php b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestChainedForm.php
index fe2d02c..a30094f 100644
--- a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestChainedForm.php
+++ b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestChainedForm.php
@@ -7,6 +7,8 @@

 /**
  * Generate form of id batch_test_chained_form.
+ *
+ * @internal
  */
 class BatchTestChainedForm extends FormBase {

diff --git a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMockForm.php b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMockForm.php
index 2d26bcf..3a185a0 100644
--- a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMockForm.php
+++ b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMockForm.php
@@ -7,6 +7,8 @@

 /**
  * Generate form of id batch_test_mock_form.
+ *
+ * @internal
  */
 class BatchTestMockForm extends FormBase {

diff --git a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMultiStepForm.php b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMultiStepForm.php
index 916831e..151b50b 100644
--- a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMultiStepForm.php
+++ b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestMultiStepForm.php
@@ -7,6 +7,8 @@

 /**
  * Generate form of id batch_test_multistep_form.
+ *
+ * @internal
  */
 class BatchTestMultiStepForm extends FormBase {

diff --git a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestSimpleForm.php b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestSimpleForm.php
index 999649d..f00d610 100644
--- a/core/modules/system/tests/modules/batch_test/src/Form/BatchTestSimpleForm.php
+++ b/core/modules/system/tests/modules/batch_test/src/Form/BatchTestSimpleForm.php
@@ -7,6 +7,8 @@

 /**
  * Generate form of id batch_test_simple_form.
+ *
+ * @internal
  */
 class BatchTestSimpleForm extends FormBase {

diff --git a/core/modules/system/tests/modules/database_test/src/Form/DatabaseTestForm.php b/core/modules/system/tests/modules/database_test/src/Form/DatabaseTestForm.php
index 12eebcc..63e2476 100644
--- a/core/modules/system/tests/modules/database_test/src/Form/DatabaseTestForm.php
+++ b/core/modules/system/tests/modules/database_test/src/Form/DatabaseTestForm.php
@@ -8,6 +8,8 @@

 /**
  * Form controller for database_test module.
+ *
+ * @internal
  */
 class DatabaseTestForm extends FormBase {

diff --git a/core/modules/system/tests/modules/entity_test/src/EntityTestDeleteForm.php b/core/modules/system/tests/modules/entity_test/src/EntityTestDeleteForm.php
index 0c24456..3896cac 100644
--- a/core/modules/system/tests/modules/entity_test/src/EntityTestDeleteForm.php
+++ b/core/modules/system/tests/modules/entity_test/src/EntityTestDeleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the entity_test delete form.
+ *
+ * @internal
  */
 class EntityTestDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/system/tests/modules/entity_test/src/EntityTestForm.php b/core/modules/system/tests/modules/entity_test/src/EntityTestForm.php
index e4c5114..75ff8ad 100644
--- a/core/modules/system/tests/modules/entity_test/src/EntityTestForm.php
+++ b/core/modules/system/tests/modules/entity_test/src/EntityTestForm.php
@@ -8,6 +8,8 @@

 /**
  * Form controller for the test entity edit forms.
+ *
+ * @internal
  */
 class EntityTestForm extends ContentEntityForm {

diff --git a/core/modules/system/tests/modules/form_test/src/ConfirmFormArrayPathTestForm.php b/core/modules/system/tests/modules/form_test/src/ConfirmFormArrayPathTestForm.php
index eaa0f20..ad830f6 100644
--- a/core/modules/system/tests/modules/form_test/src/ConfirmFormArrayPathTestForm.php
+++ b/core/modules/system/tests/modules/form_test/src/ConfirmFormArrayPathTestForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a test confirmation form with a complex cancellation destination.
+ *
+ * @internal
  */
 class ConfirmFormArrayPathTestForm extends ConfirmFormTestForm {

diff --git a/core/modules/system/tests/modules/form_test/src/ConfirmFormTestForm.php b/core/modules/system/tests/modules/form_test/src/ConfirmFormTestForm.php
index 917f9e0..c5d4cef 100644
--- a/core/modules/system/tests/modules/form_test/src/ConfirmFormTestForm.php
+++ b/core/modules/system/tests/modules/form_test/src/ConfirmFormTestForm.php
@@ -8,6 +8,8 @@

 /**
  * Provides a test confirmation form.
+ *
+ * @internal
  */
 class ConfirmFormTestForm extends ConfirmFormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestAlterForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestAlterForm.php
index e3a4038..8ffbc52 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestAlterForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestAlterForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder for testing hook_form_alter() and hook_form_FORM_ID_alter().
+ *
+ * @internal
  */
 class FormTestAlterForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestButtonClassForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestButtonClassForm.php
index 4e3de3b..f8c0820 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestButtonClassForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestButtonClassForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form to test form button classes.
+ *
+ * @internal
  */
 class FormTestButtonClassForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxForm.php
index 62220cc..15bee9c 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxForm.php
@@ -5,7 +5,11 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Symfony\Component\HttpFoundation\JsonResponse;
-
+/**
+ * Form for testing checkbox.
+ *
+ * @internal
+ */
 class FormTestCheckboxForm extends FormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxTypeJugglingForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxTypeJugglingForm.php
index ad0a86e..770170a 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxTypeJugglingForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxTypeJugglingForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a form to test return values for checkboxes.
+ *
+ * @internal
  */
 class FormTestCheckboxTypeJugglingForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesRadiosForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesRadiosForm.php
index a1a45a0..95b14ab 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesRadiosForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesRadiosForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor to test expansion of #type checkboxes and radios.
+ *
+ * @internal
  */
 class FormTestCheckboxesRadiosForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesZeroForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesZeroForm.php
index 59f81e9..6d9f1b7 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesZeroForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestCheckboxesZeroForm.php
@@ -8,6 +8,8 @@

 /**
  * Tests checkboxes zero.
+ *
+ * @internal
  */
 class FormTestCheckboxesZeroForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestClickedButtonForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestClickedButtonForm.php
index adab5bd..e95244c 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestClickedButtonForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestClickedButtonForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder to test button click detection.
+ *
+ * @internal
  */
 class FormTestClickedButtonForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestColorForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestColorForm.php
index 0763880..ce092ef 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestColorForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestColorForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor for testing #type 'color' elements.
+ *
+ * @internal
  */
 class FormTestColorForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php
index 81120ad..9da9756 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestDescriptionForm.php
@@ -8,6 +8,8 @@
 /**
  * Defines a form for testing form element description display options.
  *
+ * @internal
+ *
  * @see \Drupal\system\Tests\Form\ElementsLabelsTest::testFormDescriptions()
  */
 class FormTestDescriptionForm extends FormBase {
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php
index 5949679..839b909 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestDetailsForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form to test the #group property on #type 'container'.
+ *
+ * @internal
  */
 class FormTestDetailsForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestDisabledElementsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestDisabledElementsForm.php
index 56e6d2e..5d36779 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestDisabledElementsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestDisabledElementsForm.php
@@ -9,6 +9,8 @@

 /**
  * Builds a form to test disabled elements.
+ *
+ * @internal
  */
 class FormTestDisabledElementsForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestEmailForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestEmailForm.php
index 8e82623..8b01c32 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestEmailForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestEmailForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor for testing #type 'email' elements.
+ *
+ * @internal
  */
 class FormTestEmailForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestEmptySelectForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestEmptySelectForm.php
index 14dcb0c..acc1b11 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestEmptySelectForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestEmptySelectForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a form to test select elements when #options is not an array.
+ *
+ * @internal
  */
 class FormTestEmptySelectForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanAdvancedForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanAdvancedForm.php
index f910469..4a7c002 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanAdvancedForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanAdvancedForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder for \Drupal\Core\Form\FormState::cleanValues() test.
+ *
+ * @internal
  */
 class FormTestFormStateValuesCleanAdvancedForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanForm.php
index d5e0fd9..211cd7f 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestFormStateValuesCleanForm.php
@@ -8,6 +8,8 @@

 /**
  * Form builder for \Drupal\Core\Form\FormState::cleanValues() test.
+ *
+ * @internal
  */
 class FormTestFormStateValuesCleanForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestGetForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestGetForm.php
index 5c3decd..a032771 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestGetForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestGetForm.php
@@ -7,6 +7,8 @@

 /**
  * Form to test whether GET forms have a CSRF token.
+ *
+ * @internal
  */
 class FormTestGetForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupContainerForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupContainerForm.php
index b141b7c..4461401 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupContainerForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupContainerForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form to test the #group property on #type 'container'.
+ *
+ * @internal
  */
 class FormTestGroupContainerForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php
index 002b07d..12a05e1 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupDetailsForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form to test the #group property on #type 'details'.
+ *
+ * @internal
  */
 class FormTestGroupDetailsForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupFieldsetForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupFieldsetForm.php
index 37ef246..b37d6bb 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupFieldsetForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupFieldsetForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form to test the #group property on #type 'fieldset'.
+ *
+ * @internal
  */
 class FormTestGroupFieldsetForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupVerticalTabsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupVerticalTabsForm.php
index 2d2f98b..7a29d7d 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupVerticalTabsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestGroupVerticalTabsForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form to test the #group property on #type 'vertical_tabs'.
+ *
+ * @internal
  */
 class FormTestGroupVerticalTabsForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestInputForgeryForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestInputForgeryForm.php
index c8a82c8..da7fe2a 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestInputForgeryForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestInputForgeryForm.php
@@ -5,7 +5,11 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Symfony\Component\HttpFoundation\JsonResponse;
-
+/**
+ * Form to test input forgery.
+ *
+ * @internal
+ */
 class FormTestInputForgeryForm extends FormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestLabelForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestLabelForm.php
index 74c92ab..88de230 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestLabelForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestLabelForm.php
@@ -7,6 +7,8 @@

 /**
  * A form for testing form labels and required marks.
+ *
+ * @internal
  */
 class FormTestLabelForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestLanguageSelectForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestLanguageSelectForm.php
index ba41e19..dc0ff1b 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestLanguageSelectForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestLanguageSelectForm.php
@@ -9,6 +9,8 @@

 /**
  * Builds a form to test the language select form element.
+ *
+ * @internal
  */
 class FormTestLanguageSelectForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestLimitValidationErrorsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestLimitValidationErrorsForm.php
index deff0b4..8836022 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestLimitValidationErrorsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestLimitValidationErrorsForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form with a button triggering partial validation.
+ *
+ * @internal
  */
 class FormTestLimitValidationErrorsForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestMachineNameForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestMachineNameForm.php
index 542edc8..ee287f4 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestMachineNameForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestMachineNameForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor for testing #type 'machine_name' elements.
+ *
+ * @internal
  */
 class FormTestMachineNameForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestNumberForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestNumberForm.php
index ab28146..0965f9d 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestNumberForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestNumberForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a form to test #type 'number' and 'range' validation.
+ *
+ * @internal
  */
 class FormTestNumberForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestPatternForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestPatternForm.php
index 9180628..19157f5 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestPatternForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestPatternForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a simple form using the FAPI #pattern property.
+ *
+ * @internal
  */
 class FormTestPatternForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestPlaceholderForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestPlaceholderForm.php
index 9dd5321..af43a20 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestPlaceholderForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestPlaceholderForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a form to test the placeholder attribute.
+ *
+ * @internal
  */
 class FormTestPlaceholderForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestProgrammaticForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestProgrammaticForm.php
index 66928f0..43d7903 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestProgrammaticForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestProgrammaticForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder to test programmatic form submissions.
+ *
+ * @internal
  */
 class FormTestProgrammaticForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeForm.php
index 94240e5..1191664 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor for testing #type 'range' elements.
+ *
+ * @internal
  */
 class FormTestRangeForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeInvalidForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeInvalidForm.php
index 5415205..23c0862 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeInvalidForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRangeInvalidForm.php
@@ -7,6 +7,8 @@

 /**
  * Form constructor for testing invalid #type 'range' elements.
+ *
+ * @internal
  */
 class FormTestRangeInvalidForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRebuildPreserveValuesForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRebuildPreserveValuesForm.php
index 58934a7..662de8f 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRebuildPreserveValuesForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRebuildPreserveValuesForm.php
@@ -7,6 +7,8 @@

 /**
  * Form builder for testing preservation of values during a rebuild.
+ *
+ * @internal
  */
 class FormTestRebuildPreserveValuesForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php
index 4768acf..69b20a8 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRedirectForm.php
@@ -8,6 +8,8 @@

 /**
  * Form builder to detect form redirect.
+ *
+ * @internal
  */
 class FormTestRedirectForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestRequiredAttributeForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRequiredAttributeForm.php
index b0aa1b0..6c6ff3a 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRequiredAttributeForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRequiredAttributeForm.php
@@ -7,6 +7,8 @@

 /**
  * Builds a form to test the required attribute.
+ *
+ * @internal
  */
 class FormTestRequiredAttributeForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestResponseForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestResponseForm.php
index 0ab3a0d..a8b581b 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestResponseForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestResponseForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor for testing #type 'url' elements.
+ *
+ * @internal
  */
 class FormTestResponseForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestSelectForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestSelectForm.php
index 20242ec..20cfd23 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestSelectForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestSelectForm.php
@@ -8,6 +8,8 @@

 /**
  * Builds a form to test #type 'select' validation.
+ *
+ * @internal
  */
 class FormTestSelectForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestStatePersistForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestStatePersistForm.php
index e34af83..af7f51c 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestStatePersistForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestStatePersistForm.php
@@ -7,6 +7,8 @@

 /**
  * Form constructor for testing form state persistence.
+ *
+ * @internal
  */
 class FormTestStatePersistForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestStorageForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestStorageForm.php
index 9187012..f81658d 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestStorageForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestStorageForm.php
@@ -13,6 +13,8 @@
  * in the form storage and have to be present during any step. By setting the
  * request parameter "cache" the form can be tested with caching enabled, as
  * it would be the case, if the form would contain some #ajax callbacks.
+ *
+ * @internal
  */
 class FormTestStorageForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestStoragePageCacheForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestStoragePageCacheForm.php
index f27e5e0..2554d89 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestStoragePageCacheForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestStoragePageCacheForm.php
@@ -5,6 +5,11 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Form to test page cache storage.
+ *
+ * @internal
+ */
 class FormTestStoragePageCacheForm extends FormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableForm.php
index 758d5af..8196d4d 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableForm.php
@@ -4,6 +4,11 @@

 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Form constructor for testing #type 'table' elements.
+ *
+ * @internal
+ */
 class FormTestTableForm extends FormTestTableSelectFormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectColspanForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectColspanForm.php
index 1c9628b..becce37 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectColspanForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectColspanForm.php
@@ -4,6 +4,11 @@

 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a form to test table selects with different column spans.
+ *
+ * @internal
+ */
 class FormTestTableSelectColspanForm extends FormTestTableSelectFormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectEmptyForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectEmptyForm.php
index 199a7d3..bac78eb 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectEmptyForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectEmptyForm.php
@@ -4,6 +4,11 @@

 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a form to test table select with '#options' set to empty.
+ *
+ * @internal
+ */
 class FormTestTableSelectEmptyForm extends FormTestTableSelectFormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectFormBase.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectFormBase.php
index 9a1dc2e..af41782 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectFormBase.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectFormBase.php
@@ -7,6 +7,8 @@

 /**
  * Provides a base class for tableselect forms.
+ *
+ * @internal
  */
 abstract class FormTestTableSelectFormBase extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectJsSelectForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectJsSelectForm.php
index d6d606a..aec320e 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectJsSelectForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectJsSelectForm.php
@@ -4,6 +4,11 @@

 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a form to test table select with JS.
+ *
+ * @internal
+ */
 class FormTestTableSelectJsSelectForm extends FormTestTableSelectFormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleFalseForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleFalseForm.php
index f21ae3c..d79b235 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleFalseForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleFalseForm.php
@@ -4,6 +4,11 @@

 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a form to test table select with '#multiple" set to FALSE.
+ *
+ * @internal
+ */
 class FormTestTableSelectMultipleFalseForm extends FormTestTableSelectFormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleTrueForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleTrueForm.php
index d4a0c1d..1d46d7c 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleTrueForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestTableSelectMultipleTrueForm.php
@@ -4,6 +4,11 @@

 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a form to test table select with '#multiple' as TRUE.
+ *
+ * @internal
+ */
 class FormTestTableSelectMultipleTrueForm extends FormTestTableSelectFormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestUrlForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestUrlForm.php
index fff0e80..6ce12b4 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestUrlForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestUrlForm.php
@@ -8,6 +8,8 @@

 /**
  * Form constructor for testing #type 'url' elements.
+ *
+ * @internal
  */
 class FormTestUrlForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateForm.php
index 41772da..7123ace 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateForm.php
@@ -17,6 +17,8 @@
  *   structure and the alterations should be contained in the rebuilt form.
  * - #validate handlers should be able to alter the $form and the alterations
  *   should be contained in the rebuilt form.
+ *
+ * @internal
  */
 class FormTestValidateForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateNoToken.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateNoToken.php
index 1e996ee..c4b568e 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateNoToken.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateNoToken.php
@@ -7,6 +7,8 @@

 /**
  * Form to test the validation of forms with a disabled CSRF token.
+ *
+ * @internal
  */
 class FormTestValidateNoToken extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredForm.php
index 88e6b35..13aec60 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredForm.php
@@ -7,6 +7,8 @@

 /**
  * Form constructor to test the #required property.
+ *
+ * @internal
  */
 class FormTestValidateRequiredForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredNoTitleForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredNoTitleForm.php
index 29b3b5f..1829ab2 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredNoTitleForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestValidateRequiredNoTitleForm.php
@@ -7,6 +7,8 @@

 /**
  * Form constructor to test the #required property without #title.
+ *
+ * @internal
  */
 class FormTestValidateRequiredNoTitleForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsAccessForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsAccessForm.php
index cb171a6..1b343fc 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsAccessForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsAccessForm.php
@@ -5,6 +5,11 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a form to test vertical tabs access.
+ *
+ * @internal
+ */
 class FormTestVerticalTabsAccessForm extends FormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php
index b89636a..fbd7160 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestVerticalTabsForm.php
@@ -5,6 +5,11 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;

+/**
+ * Builds a simple form to test vertical tabs.
+ *
+ * @internal
+ */
 class FormTestVerticalTabsForm extends FormBase {

   /**
diff --git a/core/modules/system/tests/modules/form_test/src/Form/RedirectBlockForm.php b/core/modules/system/tests/modules/form_test/src/Form/RedirectBlockForm.php
index 163ac22..842abd7 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/RedirectBlockForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/RedirectBlockForm.php
@@ -8,6 +8,8 @@
 /**
  * Builds a simple form that redirects on submit.
  *
+ * @internal
+ *
  * @see \Drupal\form_test\Plugin\Block\RedirectFormBlock
  */
 class RedirectBlockForm extends FormBase {
diff --git a/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php b/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php
index 7531ca8..0d86a2d 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestArgumentsObject.php
@@ -7,6 +7,8 @@

 /**
  * Provides a test form object that needs arguments.
+ *
+ * @internal
  */
 class FormTestArgumentsObject extends ConfigFormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/FormTestAutocompleteForm.php b/core/modules/system/tests/modules/form_test/src/FormTestAutocompleteForm.php
index 019513d..bde049e 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestAutocompleteForm.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestAutocompleteForm.php
@@ -7,6 +7,8 @@

 /**
  * Defines a test form using autocomplete textfields.
+ *
+ * @internal
  */
 class FormTestAutocompleteForm extends FormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php b/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php
index 7573253..40d474d 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestControllerObject.php
@@ -9,6 +9,8 @@

 /**
  * Provides a test form object.
+ *
+ * @internal
  */
 class FormTestControllerObject extends ConfigFormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/FormTestObject.php b/core/modules/system/tests/modules/form_test/src/FormTestObject.php
index f99fbe7..d7fd119 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestObject.php
@@ -7,6 +7,8 @@

 /**
  * Provides a test form object.
+ *
+ * @internal
  */
 class FormTestObject extends ConfigFormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php b/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php
index effd319..c1d8555 100644
--- a/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php
+++ b/core/modules/system/tests/modules/form_test/src/FormTestServiceObject.php
@@ -7,6 +7,8 @@

 /**
  * Provides a test form object.
+ *
+ * @internal
  */
 class FormTestServiceObject extends ConfigFormBase {

diff --git a/core/modules/system/tests/modules/form_test/src/SystemConfigFormTestForm.php b/core/modules/system/tests/modules/form_test/src/SystemConfigFormTestForm.php
index f393bea..0a2855b 100644
--- a/core/modules/system/tests/modules/form_test/src/SystemConfigFormTestForm.php
+++ b/core/modules/system/tests/modules/form_test/src/SystemConfigFormTestForm.php
@@ -6,6 +6,8 @@

 /**
  * Tests the ConfigFormBase class.
+ *
+ * @internal
  */
 class SystemConfigFormTestForm extends ConfigFormBase {

diff --git a/core/modules/system/tests/modules/js_webassert_test/src/Form/JsWebAssertTestForm.php b/core/modules/system/tests/modules/js_webassert_test/src/Form/JsWebAssertTestForm.php
index 087378b..d46db77 100644
--- a/core/modules/system/tests/modules/js_webassert_test/src/Form/JsWebAssertTestForm.php
+++ b/core/modules/system/tests/modules/js_webassert_test/src/Form/JsWebAssertTestForm.php
@@ -8,6 +8,8 @@

 /**
  * Test form for JSWebAssert JavaScriptTestBase.
+ *
+ * @internal
  */
 class JsWebAssertTestForm extends FormBase {

diff --git a/core/modules/system/tests/modules/session_test/src/Form/SessionTestForm.php b/core/modules/system/tests/modules/session_test/src/Form/SessionTestForm.php
index bf250ac..c09237a 100644
--- a/core/modules/system/tests/modules/session_test/src/Form/SessionTestForm.php
+++ b/core/modules/system/tests/modules/session_test/src/Form/SessionTestForm.php
@@ -8,6 +8,8 @@

 /**
  * Form controller for the test config edit forms.
+ *
+ * @internal
  */
 class SessionTestForm extends FormBase {

diff --git a/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php b/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php
index 24a9bdb..01eb8be 100644
--- a/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php
+++ b/core/modules/system/tests/modules/test_page_test/src/Form/TestForm.php
@@ -7,6 +7,8 @@

 /**
  * Defines a test form for testing assertions.
+ *
+ * @internal
  */
 class TestForm extends FormBase {

diff --git a/core/modules/taxonomy/src/Form/OverviewTerms.php b/core/modules/taxonomy/src/Form/OverviewTerms.php
index 0ccb24b..bcf6018 100644
--- a/core/modules/taxonomy/src/Form/OverviewTerms.php
+++ b/core/modules/taxonomy/src/Form/OverviewTerms.php
@@ -11,6 +11,8 @@

 /**
  * Provides terms overview form for a taxonomy vocabulary.
+ *
+ * @internal
  */
 class OverviewTerms extends FormBase {

diff --git a/core/modules/taxonomy/src/Form/TermDeleteForm.php b/core/modules/taxonomy/src/Form/TermDeleteForm.php
index 0e97ff6..b50a5da 100644
--- a/core/modules/taxonomy/src/Form/TermDeleteForm.php
+++ b/core/modules/taxonomy/src/Form/TermDeleteForm.php
@@ -8,6 +8,8 @@

 /**
  * Provides a deletion confirmation form for taxonomy term.
+ *
+ * @internal
  */
 class TermDeleteForm extends ContentEntityDeleteForm {

diff --git a/core/modules/taxonomy/src/Form/VocabularyDeleteForm.php b/core/modules/taxonomy/src/Form/VocabularyDeleteForm.php
index 7c91b78..7bca948 100644
--- a/core/modules/taxonomy/src/Form/VocabularyDeleteForm.php
+++ b/core/modules/taxonomy/src/Form/VocabularyDeleteForm.php
@@ -6,6 +6,8 @@

 /**
  * Provides a deletion confirmation form for taxonomy vocabulary.
+ *
+ * @internal
  */
 class VocabularyDeleteForm extends EntityDeleteForm {

diff --git a/core/modules/taxonomy/src/Form/VocabularyResetForm.php b/core/modules/taxonomy/src/Form/VocabularyResetForm.php
index e036ff9..439d994 100644
--- a/core/modules/taxonomy/src/Form/VocabularyResetForm.php
+++ b/core/modules/taxonomy/src/Form/VocabularyResetForm.php
@@ -9,6 +9,8 @@

 /**
  * Provides confirmation form for resetting a vocabulary to alphabetical order.
+ *
+ * @internal
  */
 class VocabularyResetForm extends EntityConfirmFormBase {

diff --git a/core/modules/taxonomy/src/TermForm.php b/core/modules/taxonomy/src/TermForm.php
index 1eae95a..bb0b10e 100644
--- a/core/modules/taxonomy/src/TermForm.php
+++ b/core/modules/taxonomy/src/TermForm.php
@@ -7,6 +7,8 @@

 /**
  * Base for handler for taxonomy term edit forms.
+ *
+ * @internal
  */
 class TermForm extends ContentEntityForm {

diff --git a/core/modules/taxonomy/src/VocabularyForm.php b/core/modules/taxonomy/src/VocabularyForm.php
index 63f0ccb..23e911b 100644
--- a/core/modules/taxonomy/src/VocabularyForm.php
+++ b/core/modules/taxonomy/src/VocabularyForm.php
@@ -11,6 +11,8 @@

 /**
  * Base form for vocabulary edit forms.
+ *
+ * @internal
  */
 class VocabularyForm extends BundleEntityFormBase {

diff --git a/core/modules/update/src/Form/UpdateManagerInstall.php b/core/modules/update/src/Form/UpdateManagerInstall.php
index b141182..d60b7c2 100644
--- a/core/modules/update/src/Form/UpdateManagerInstall.php
+++ b/core/modules/update/src/Form/UpdateManagerInstall.php
@@ -12,6 +12,8 @@

 /**
  * Configure update settings for this site.
+ *
+ * @internal
  */
 class UpdateManagerInstall extends FormBase {

diff --git a/core/modules/update/src/Form/UpdateManagerUpdate.php b/core/modules/update/src/Form/UpdateManagerUpdate.php
index db497c2..0479506 100644
--- a/core/modules/update/src/Form/UpdateManagerUpdate.php
+++ b/core/modules/update/src/Form/UpdateManagerUpdate.php
@@ -11,6 +11,8 @@

 /**
  * Configure update settings for this site.
+ *
+ * @internal
  */
 class UpdateManagerUpdate extends FormBase {

diff --git a/core/modules/update/src/Form/UpdateReady.php b/core/modules/update/src/Form/UpdateReady.php
index ef9a2f1..9dad022 100644
--- a/core/modules/update/src/Form/UpdateReady.php
+++ b/core/modules/update/src/Form/UpdateReady.php
@@ -13,6 +13,8 @@

 /**
  * Configure update settings for this site.
+ *
+ * @internal
  */
 class UpdateReady extends FormBase {

diff --git a/core/modules/update/src/UpdateSettingsForm.php b/core/modules/update/src/UpdateSettingsForm.php
index 1860269..ac8981c 100644
--- a/core/modules/update/src/UpdateSettingsForm.php
+++ b/core/modules/update/src/UpdateSettingsForm.php
@@ -10,6 +10,8 @@

 /**
  * Configure update settings for this site.
+ *
+ * @internal
  */
 class UpdateSettingsForm extends ConfigFormBase implements ContainerInjectionInterface {

diff --git a/core/modules/user/src/AccountForm.php b/core/modules/user/src/AccountForm.php
index f5e2e49..ef4fd8a 100644
--- a/core/modules/user/src/AccountForm.php
+++ b/core/modules/user/src/AccountForm.php
@@ -18,6 +18,8 @@

 /**
  * Form controller for the user account forms.
+ *
+ * @internal
  */
 abstract class AccountForm extends ContentEntityForm {

diff --git a/core/modules/user/src/AccountSettingsForm.php b/core/modules/user/src/AccountSettingsForm.php
index eacc378..bd80dd7 100644
--- a/core/modules/user/src/AccountSettingsForm.php
+++ b/core/modules/user/src/AccountSettingsForm.php
@@ -11,6 +11,8 @@

 /**
  * Configure user settings for this site.
+ *
+ * @internal
  */
 class AccountSettingsForm extends ConfigFormBase {

diff --git a/core/modules/user/src/Form/UserCancelForm.php b/core/modules/user/src/Form/UserCancelForm.php
index 14c553c..da7a5f4 100644
--- a/core/modules/user/src/Form/UserCancelForm.php
+++ b/core/modules/user/src/Form/UserCancelForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides a confirmation form for cancelling user account.
+ *
+ * @internal
  */
 class UserCancelForm extends ContentEntityConfirmFormBase {

diff --git a/core/modules/user/src/Form/UserLoginForm.php b/core/modules/user/src/Form/UserLoginForm.php
index 25a54ec..703e0ce 100644
--- a/core/modules/user/src/Form/UserLoginForm.php
+++ b/core/modules/user/src/Form/UserLoginForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a user login form.
+ *
+ * @internal
  */
 class UserLoginForm extends FormBase {

diff --git a/core/modules/user/src/Form/UserMultipleCancelConfirm.php b/core/modules/user/src/Form/UserMultipleCancelConfirm.php
index 62a64e5..985d199 100644
--- a/core/modules/user/src/Form/UserMultipleCancelConfirm.php
+++ b/core/modules/user/src/Form/UserMultipleCancelConfirm.php
@@ -12,6 +12,8 @@

 /**
  * Provides a confirmation form for cancelling multiple user accounts.
+ *
+ * @internal
  */
 class UserMultipleCancelConfirm extends ConfirmFormBase {

diff --git a/core/modules/user/src/Form/UserPasswordForm.php b/core/modules/user/src/Form/UserPasswordForm.php
index ea224fe..45e33b3 100644
--- a/core/modules/user/src/Form/UserPasswordForm.php
+++ b/core/modules/user/src/Form/UserPasswordForm.php
@@ -11,6 +11,8 @@

 /**
  * Provides a user password reset form.
+ *
+ * @internal
  */
 class UserPasswordForm extends FormBase {

diff --git a/core/modules/user/src/Form/UserPasswordResetForm.php b/core/modules/user/src/Form/UserPasswordResetForm.php
index ce8c7cc..bf9538c 100644
--- a/core/modules/user/src/Form/UserPasswordResetForm.php
+++ b/core/modules/user/src/Form/UserPasswordResetForm.php
@@ -9,6 +9,8 @@

 /**
  * Form controller for the user password forms.
+ *
+ * @internal
  */
 class UserPasswordResetForm extends FormBase {

diff --git a/core/modules/user/src/Form/UserPermissionsForm.php b/core/modules/user/src/Form/UserPermissionsForm.php
index 3c5e46b..d0e9d0d 100644
--- a/core/modules/user/src/Form/UserPermissionsForm.php
+++ b/core/modules/user/src/Form/UserPermissionsForm.php
@@ -11,6 +11,8 @@

 /**
  * Provides the user permissions administration form.
+ *
+ * @internal
  */
 class UserPermissionsForm extends FormBase {

diff --git a/core/modules/user/src/Form/UserPermissionsRoleSpecificForm.php b/core/modules/user/src/Form/UserPermissionsRoleSpecificForm.php
index 4281a44..1571649 100644
--- a/core/modules/user/src/Form/UserPermissionsRoleSpecificForm.php
+++ b/core/modules/user/src/Form/UserPermissionsRoleSpecificForm.php
@@ -7,6 +7,8 @@

 /**
  * Provides the user permissions administration form for a specific role.
+ *
+ * @internal
  */
 class UserPermissionsRoleSpecificForm extends UserPermissionsForm {

diff --git a/core/modules/user/src/ProfileForm.php b/core/modules/user/src/ProfileForm.php
index 343d4d0..c856b75 100644
--- a/core/modules/user/src/ProfileForm.php
+++ b/core/modules/user/src/ProfileForm.php
@@ -6,6 +6,8 @@

 /**
  * Form handler for the profile forms.
+ *
+ * @internal
  */
 class ProfileForm extends AccountForm {

diff --git a/core/modules/user/src/RegisterForm.php b/core/modules/user/src/RegisterForm.php
index 7a97974..4974e69 100644
--- a/core/modules/user/src/RegisterForm.php
+++ b/core/modules/user/src/RegisterForm.php
@@ -6,6 +6,8 @@

 /**
  * Form handler for the user register forms.
+ *
+ * @internal
  */
 class RegisterForm extends AccountForm {

diff --git a/core/modules/user/src/RoleForm.php b/core/modules/user/src/RoleForm.php
index 7e78853..e40067c 100644
--- a/core/modules/user/src/RoleForm.php
+++ b/core/modules/user/src/RoleForm.php
@@ -7,6 +7,8 @@

 /**
  * Form controller for the role entity edit forms.
+ *
+ * @internal
  */
 class RoleForm extends EntityForm {

diff --git a/core/modules/views/src/Form/ViewsExposedForm.php b/core/modules/views/src/Form/ViewsExposedForm.php
index 44e7ec4..459708a 100644
--- a/core/modules/views/src/Form/ViewsExposedForm.php
+++ b/core/modules/views/src/Form/ViewsExposedForm.php
@@ -12,6 +12,8 @@

 /**
  * Provides the views exposed form.
+ *
+ * @internal
  */
 class ViewsExposedForm extends FormBase {

diff --git a/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementEmbedForm.php b/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementEmbedForm.php
index 80d19d1..03e9591 100644
--- a/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementEmbedForm.php
+++ b/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementEmbedForm.php
@@ -7,6 +7,8 @@

 /**
  * Simple form page callback to test the view element.
+ *
+ * @internal
  */
 class ViewsTestDataElementEmbedForm extends FormBase {

diff --git a/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementForm.php b/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementForm.php
index 78aa998..7269cba 100644
--- a/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementForm.php
+++ b/core/modules/views/tests/modules/views_test_data/src/Form/ViewsTestDataElementForm.php
@@ -7,6 +7,8 @@

 /**
  * Simple form page callback to test the view element.
+ *
+ * @internal
  */
 class ViewsTestDataElementForm extends FormBase {

diff --git a/core/modules/views_ui/src/Form/AdvancedSettingsForm.php b/core/modules/views_ui/src/Form/AdvancedSettingsForm.php
index 36f34c2..e4aa1c1 100644
--- a/core/modules/views_ui/src/Form/AdvancedSettingsForm.php
+++ b/core/modules/views_ui/src/Form/AdvancedSettingsForm.php
@@ -8,6 +8,8 @@

 /**
  * Form builder for the advanced admin settings page.
+ *
+ * @internal
  */
 class AdvancedSettingsForm extends ConfigFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/AddHandler.php b/core/modules/views_ui/src/Form/Ajax/AddHandler.php
index 0a04000..7bfd772 100644
--- a/core/modules/views_ui/src/Form/Ajax/AddHandler.php
+++ b/core/modules/views_ui/src/Form/Ajax/AddHandler.php
@@ -9,6 +9,8 @@

 /**
  * Provides a form for adding an item in the Views UI.
+ *
+ * @internal
  */
 class AddHandler extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/Analyze.php b/core/modules/views_ui/src/Form/Ajax/Analyze.php
index 52784d3..0c630df 100644
--- a/core/modules/views_ui/src/Form/Ajax/Analyze.php
+++ b/core/modules/views_ui/src/Form/Ajax/Analyze.php
@@ -7,6 +7,8 @@

 /**
  * Displays analysis information for a view.
+ *
+ * @internal
  */
 class Analyze extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/ConfigHandler.php b/core/modules/views_ui/src/Form/Ajax/ConfigHandler.php
index 972b4b9..5d68f0b 100644
--- a/core/modules/views_ui/src/Form/Ajax/ConfigHandler.php
+++ b/core/modules/views_ui/src/Form/Ajax/ConfigHandler.php
@@ -10,6 +10,8 @@

 /**
  * Provides a form for configuring an item in the Views UI.
+ *
+ * @internal
  */
 class ConfigHandler extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/ConfigHandlerExtra.php b/core/modules/views_ui/src/Form/Ajax/ConfigHandlerExtra.php
index a79d031..8e71123 100644
--- a/core/modules/views_ui/src/Form/Ajax/ConfigHandlerExtra.php
+++ b/core/modules/views_ui/src/Form/Ajax/ConfigHandlerExtra.php
@@ -8,6 +8,8 @@

 /**
  * Provides a form for configuring extra information for a Views UI item.
+ *
+ * @internal
  */
 class ConfigHandlerExtra extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/ConfigHandlerGroup.php b/core/modules/views_ui/src/Form/Ajax/ConfigHandlerGroup.php
index b4d0f13..b208139 100644
--- a/core/modules/views_ui/src/Form/Ajax/ConfigHandlerGroup.php
+++ b/core/modules/views_ui/src/Form/Ajax/ConfigHandlerGroup.php
@@ -9,6 +9,8 @@

 /**
  * Provides a form for configuring grouping information for a Views UI handler.
+ *
+ * @internal
  */
 class ConfigHandlerGroup extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/Display.php b/core/modules/views_ui/src/Form/Ajax/Display.php
index 302d759..3f75a30 100644
--- a/core/modules/views_ui/src/Form/Ajax/Display.php
+++ b/core/modules/views_ui/src/Form/Ajax/Display.php
@@ -7,6 +7,8 @@

 /**
  * Provides a form for editing the Views display.
+ *
+ * @internal
  */
 class Display extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/EditDetails.php b/core/modules/views_ui/src/Form/Ajax/EditDetails.php
index 07b1625..fca2099 100644
--- a/core/modules/views_ui/src/Form/Ajax/EditDetails.php
+++ b/core/modules/views_ui/src/Form/Ajax/EditDetails.php
@@ -7,6 +7,8 @@

 /**
  * Provides a form for editing the details of a View.
+ *
+ * @internal
  */
 class EditDetails extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/Rearrange.php b/core/modules/views_ui/src/Form/Ajax/Rearrange.php
index 2a46120..5a8468e 100644
--- a/core/modules/views_ui/src/Form/Ajax/Rearrange.php
+++ b/core/modules/views_ui/src/Form/Ajax/Rearrange.php
@@ -10,6 +10,8 @@

 /**
  * Provides a rearrange form for Views handlers.
+ *
+ * @internal
  */
 class Rearrange extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/RearrangeFilter.php b/core/modules/views_ui/src/Form/Ajax/RearrangeFilter.php
index 3298681..67ddbe8 100644
--- a/core/modules/views_ui/src/Form/Ajax/RearrangeFilter.php
+++ b/core/modules/views_ui/src/Form/Ajax/RearrangeFilter.php
@@ -8,6 +8,8 @@

 /**
  * Provides a rearrange form for Views filters.
+ *
+ * @internal
  */
 class RearrangeFilter extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/ReorderDisplays.php b/core/modules/views_ui/src/Form/Ajax/ReorderDisplays.php
index 377a3d5..c9ad413 100644
--- a/core/modules/views_ui/src/Form/Ajax/ReorderDisplays.php
+++ b/core/modules/views_ui/src/Form/Ajax/ReorderDisplays.php
@@ -8,6 +8,8 @@

 /**
  * Displays the display reorder form.
+ *
+ * @internal
  */
 class ReorderDisplays extends ViewsFormBase {

diff --git a/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php b/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
index 375766a..213981d 100644
--- a/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
+++ b/core/modules/views_ui/src/Form/Ajax/ViewsFormBase.php
@@ -21,6 +21,8 @@

 /**
  * Provides a base class for Views UI AJAX forms.
+ *
+ * @internal
  */
 abstract class ViewsFormBase extends FormBase implements ViewsFormInterface {

diff --git a/core/modules/views_ui/src/Form/BasicSettingsForm.php b/core/modules/views_ui/src/Form/BasicSettingsForm.php
index bcd5336..5b7bfd7 100644
--- a/core/modules/views_ui/src/Form/BasicSettingsForm.php
+++ b/core/modules/views_ui/src/Form/BasicSettingsForm.php
@@ -10,6 +10,8 @@

 /**
  * Form builder for the admin display defaults page.
+ *
+ * @internal
  */
 class BasicSettingsForm extends ConfigFormBase {

diff --git a/core/modules/views_ui/src/Form/BreakLockForm.php b/core/modules/views_ui/src/Form/BreakLockForm.php
index 94a626f..cc4ae9d 100644
--- a/core/modules/views_ui/src/Form/BreakLockForm.php
+++ b/core/modules/views_ui/src/Form/BreakLockForm.php
@@ -10,6 +10,8 @@

 /**
  * Builds the form to break the lock of an edited view.
+ *
+ * @internal
  */
 class BreakLockForm extends EntityConfirmFormBase {

diff --git a/core/modules/views_ui/src/ViewAddForm.php b/core/modules/views_ui/src/ViewAddForm.php
index 429032c..e76621f 100644
--- a/core/modules/views_ui/src/ViewAddForm.php
+++ b/core/modules/views_ui/src/ViewAddForm.php
@@ -10,6 +10,8 @@

 /**
  * Form controller for the Views edit form.
+ *
+ * @internal
  */
 class ViewAddForm extends ViewFormBase {

diff --git a/core/modules/views_ui/src/ViewDuplicateForm.php b/core/modules/views_ui/src/ViewDuplicateForm.php
index fa2db60..9cfe341 100644
--- a/core/modules/views_ui/src/ViewDuplicateForm.php
+++ b/core/modules/views_ui/src/ViewDuplicateForm.php
@@ -6,6 +6,8 @@

 /**
  * Form controller for the Views duplicate form.
+ *
+ * @internal
  */
 class ViewDuplicateForm extends ViewFormBase {

diff --git a/core/modules/views_ui/src/ViewEditForm.php b/core/modules/views_ui/src/ViewEditForm.php
index 67d1229..23d921c 100644
--- a/core/modules/views_ui/src/ViewEditForm.php
+++ b/core/modules/views_ui/src/ViewEditForm.php
@@ -18,6 +18,8 @@

 /**
  * Form controller for the Views edit form.
+ *
+ * @internal
  */
 class ViewEditForm extends ViewFormBase {

diff --git a/core/modules/views_ui/src/ViewFormBase.php b/core/modules/views_ui/src/ViewFormBase.php
index 49cdc49..09aa644 100644
--- a/core/modules/views_ui/src/ViewFormBase.php
+++ b/core/modules/views_ui/src/ViewFormBase.php
@@ -9,6 +9,8 @@

 /**
  * Base form for Views forms.
+ *
+ * @internal
  */
 abstract class ViewFormBase extends EntityForm {

diff --git a/core/modules/views_ui/src/ViewPreviewForm.php b/core/modules/views_ui/src/ViewPreviewForm.php
index 2cc2533..4bc8eaa 100644
--- a/core/modules/views_ui/src/ViewPreviewForm.php
+++ b/core/modules/views_ui/src/ViewPreviewForm.php
@@ -7,6 +7,8 @@

 /**
  * Form controller for the Views preview form.
+ *
+ * @internal
  */
 class ViewPreviewForm extends ViewFormBase {

diff --git a/core/modules/workflows/src/Form/WorkflowAddForm.php b/core/modules/workflows/src/Form/WorkflowAddForm.php
index 56cbf69..7039dc4 100644
--- a/core/modules/workflows/src/Form/WorkflowAddForm.php
+++ b/core/modules/workflows/src/Form/WorkflowAddForm.php
@@ -11,6 +11,8 @@

 /**
  * Form for adding workflows.
+ *
+ * @internal
  */
 class WorkflowAddForm extends EntityForm {

diff --git a/core/modules/workflows/src/Form/WorkflowDeleteForm.php b/core/modules/workflows/src/Form/WorkflowDeleteForm.php
index b9b8331..66eb66d 100644
--- a/core/modules/workflows/src/Form/WorkflowDeleteForm.php
+++ b/core/modules/workflows/src/Form/WorkflowDeleteForm.php
@@ -8,6 +8,8 @@

 /**
  * Builds the form to delete Workflow entities.
+ *
+ * @internal
  */
 class WorkflowDeleteForm extends EntityConfirmFormBase {

diff --git a/core/modules/workflows/src/Form/WorkflowEditForm.php b/core/modules/workflows/src/Form/WorkflowEditForm.php
index 764c0c9..54ca7b1 100644
--- a/core/modules/workflows/src/Form/WorkflowEditForm.php
+++ b/core/modules/workflows/src/Form/WorkflowEditForm.php
@@ -13,6 +13,8 @@

 /**
  * The form for editing workflows.
+ *
+ * @internal
  */
 class WorkflowEditForm extends EntityForm {

diff --git a/core/modules/workflows/src/Form/WorkflowStateAddForm.php b/core/modules/workflows/src/Form/WorkflowStateAddForm.php
index 0b36858..3d95d6c 100644
--- a/core/modules/workflows/src/Form/WorkflowStateAddForm.php
+++ b/core/modules/workflows/src/Form/WorkflowStateAddForm.php
@@ -8,6 +8,8 @@

 /**
  * Class WorkflowStateAddForm.
+ *
+ * @internal
  */
 class WorkflowStateAddForm extends EntityForm {

diff --git a/core/modules/workflows/src/Form/WorkflowStateDeleteForm.php b/core/modules/workflows/src/Form/WorkflowStateDeleteForm.php
index c60045c..81d5044 100644
--- a/core/modules/workflows/src/Form/WorkflowStateDeleteForm.php
+++ b/core/modules/workflows/src/Form/WorkflowStateDeleteForm.php
@@ -9,6 +9,8 @@

 /**
  * Builds the form to delete states from Workflow entities.
+ *
+ * @internal
  */
 class WorkflowStateDeleteForm extends ConfirmFormBase {

diff --git a/core/modules/workflows/src/Form/WorkflowStateEditForm.php b/core/modules/workflows/src/Form/WorkflowStateEditForm.php
index f21508f..e9ef87d 100644
--- a/core/modules/workflows/src/Form/WorkflowStateEditForm.php
+++ b/core/modules/workflows/src/Form/WorkflowStateEditForm.php
@@ -9,6 +9,8 @@

 /**
  * Class WorkflowStateEditForm.
+ *
+ * @internal
  */
 class WorkflowStateEditForm extends EntityForm {

diff --git a/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php b/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php
index fe3a406..b067c11 100644
--- a/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php
+++ b/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php
@@ -9,6 +9,8 @@

 /**
  * Class WorkflowTransitionAddForm.
+ *
+ * @internal
  */
 class WorkflowTransitionAddForm extends EntityForm {

diff --git a/core/modules/workflows/src/Form/WorkflowTransitionDeleteForm.php b/core/modules/workflows/src/Form/WorkflowTransitionDeleteForm.php
index abcb41e..2b91417 100644
--- a/core/modules/workflows/src/Form/WorkflowTransitionDeleteForm.php
+++ b/core/modules/workflows/src/Form/WorkflowTransitionDeleteForm.php
@@ -9,6 +9,8 @@

 /**
  * Builds the form to delete transitions from Workflow entities.
+ *
+ * @internal
  */
 class WorkflowTransitionDeleteForm extends ConfirmFormBase {

diff --git a/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php b/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php
index 5bbabae..388ee8b 100644
--- a/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php
+++ b/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php
@@ -10,6 +10,8 @@

 /**
  * Class WorkflowTransitionEditForm.
+ *
+ * @internal
  */
 class WorkflowTransitionEditForm extends EntityForm {

diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityResolverManagerTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityResolverManagerTest.php
index d2e5eae..ee02cae 100644
--- a/core/tests/Drupal/Tests/Core/Entity/EntityResolverManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityResolverManagerTest.php
@@ -492,6 +492,8 @@ class SimpleTestEntity extends Entity {

 /**
  * A basic form with a passed entity with an interface.
+ *
+ * @internal
  */
 class BasicForm extends FormBase {

diff --git a/core/modules/statistics/src/StatisticsSettingsForm.php b/core/modules/statistics/src/StatisticsSettingsForm.php
index 4c06e0b1de..85c455bfae 100644
--- a/core/modules/statistics/src/StatisticsSettingsForm.php
+++ b/core/modules/statistics/src/StatisticsSettingsForm.php
@@ -10,6 +10,8 @@

 /**
  * Configure statistics settings for this site.
+ *
+ * @internal
  */
 class StatisticsSettingsForm extends ConfigFormBase {

diff --git a/core/modules/system/src/Form/CronForm.php b/core/modules/system/src/Form/CronForm.php
index 8a3f23175c..88f6bd8856 100644
--- a/core/modules/system/src/Form/CronForm.php
+++ b/core/modules/system/src/Form/CronForm.php
@@ -14,6 +14,8 @@

 /**
  * Configure cron settings for this site.
+ *
+ * @internal
  */
 class CronForm extends FormBase {

