diff --git a/core/lib/Drupal/Core/Entity/ContentEntityDeleteForm.php b/core/lib/Drupal/Core/Entity/ContentEntityDeleteForm.php
index 9a70ef5bc78ccfae3f8aa6e50cf7519632a4d8d1..32c48d8a03d16df20b84a78fa0f525350f2bfc11 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/EntityDeleteForm.php b/core/lib/Drupal/Core/Entity/EntityDeleteForm.php
index b7a66e32f01272bf57764f6b9d7262c80f551b9f..6dd08f2b07e8e281d92dd1fc5d7034026ecb9597 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/FileTransfer/Form/FileTransferAuthorizeForm.php b/core/lib/Drupal/Core/FileTransfer/Form/FileTransferAuthorizeForm.php
index 2adbd1f0f0b78ed1f62b34cb3a9117518afe3044..3f8fd6d36442899c64fed2abf4dc0f26436dd4e5 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/Installer/Form/SelectLanguageForm.php b/core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php
index 686b1a2c34371fe0a941df5ca42b49a9770c8aff..55b7cbeea7c51bf0cadda2a073ce6aea573ba52e 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 679e6db00b2ff18895c2b2a8814870091ca6c1e9..ea209ad2c877a27a009c5dd62d584e07648e661f 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 540da5598db4b188811b2840db0c3c0fb5d9d99e..075c982773e93a0e3e1ce77a4e3da6607f204561 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 8d588d48802f567f9151ea42a5612c09725cc387..300def99319f9423a314370bbba51eb1dd54b587 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 25aaebc315d83ccb95b9853e42ea2cd7b69dcb1e..e7dbb8ce19a2a134ed6ebb427c4673b60db39d9a 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 8053605c8f3585349ce5bcce39c0f796754a700f..01f5a9d20d8c20ea20abdca62b770934fa113588 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/Form/ActionAdminManageForm.php b/core/modules/action/src/Form/ActionAdminManageForm.php
index 478e919be04567e51c1f2b075ef9266040a05fa4..08d2e7c4fb2e3bf9673bc075e34d7ac6a417111e 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 9e7f0a529a031bcea8ef04d59addd1036de47637..0821b90a7a6b46d68fe54dc81559c7655e37479a 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 1580a307dc1fa80043ca254b1d90ad7f5c558e3b..aed2cd19c359524676170345d471153c5bd762f6 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 17a179864fc7adbfdb67c62ff4deca5a33f742f6..53eaf3c1730370235d9a6abf451361ddfa39eea4 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 48c83dc8386930408df0888060f3401797009cf3..9f4087e9395d59c0b19820bec6b62fbad75815ef 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 59e70d9727abadcf9a3929c9ee055c5ec386aeaf..60a189936240703f61db2ac55e96f5e39b4dc70e 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 48b2dfe87e28f0d1140b1e78580dcc280580f081..3014c5b9beb3d5b99905b1f475dcb4dba999849c 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 731d06518c8ac29cf66a653d7ea083e73279e813..5d8e7957f8064af857170cf85addd898545a5811 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 3d14ca3415398d5707d803255a2e2eee9ddbfd9e..2d5731f139940703c177bdc53dbff0f10bb37636 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 9770762fef2ccd57798273b1faf1566893ebd1f1..2454a14f8492b460d7eab783946dc00a61af66cf 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
@@ -5,6 +5,11 @@
 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 b2d180aa4671450b72e59447cd249f0190dddcf1..04160432de13b9e7010ccb237158e2da5fa78a87 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 5209b329bf14b8def37a45c91145e714a5b47e21..e128ea7e7ec2d33eefd56e90aa30d23382e2ac43 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 9aa74c65b3ea68e7468a106f1a16cb66d69189b4..3ad55edff2c1cfe76ac56f44f64907b28d683b5d 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
@@ -5,6 +5,11 @@
 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 08fd6f69a0ffdea9c87974d3e6ffd7d285d9e415..7fa645df5fbafa857ea006b32910ad316add4fb2 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
@@ -5,6 +5,11 @@
 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 eefd4e9790847de64f8a84f35cd465ae435e7252..225dc91b4671bce46dd43f0c26a60d81e349b0c5 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 4e140b19322efceccfdde2417094a344958bdd1a..6e17a62ae241ce19ea1df6e392db2dbac007b137 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 035ec4c2fb506665efe4765904e569c74e259a8b..fe0759cc16d501b9cecb61fec7a481b6de6d98ce 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 aea4ab5e835f8987dfb2851ff55f679a3c8a1e21..34da0a987419d208089910ddeebb3274da7342aa 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 1e7cdb4b95a417717a5f4346d820a6116789cb1f..66e717eaba620fae390c69a12bc7b3ca09e8a1ed 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 1d63aacf0c08a3588574138e64ab29e665afe92a..f7ea043ed2ebf6d3ccbdc97807c62a67b828d5fe 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 e31c0940e824ce02aaf5c920c69a97686bb8255d..f61aa775a5abd2ee9a42a1307f6e49f44b50b50d 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 29590ccdb573d88e1c80dcb5808390b4b59d001d..3189ef519e2fe071bab997c4a01e48311e373bea 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 7b6d5925379b6eec32ade5105e3c57a0d7aad488..e8c066825a7175a88d398aac847f3971e27488c0 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 28231b8cb7793f648795689ef0893869696c5e0f..98e9ddef96da6f0e2c86a117dcb09e1cf277c154 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 9cb147f7f0e398b5f7b3b9c9a66f060694055baf..0ac5b446bd556fe04ecdb183fc70e76f40107c5d 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 b18bf3d0b0c6be258c09d8839a4e739f16686f35..1ffa2c618ab66ac064c7384a1f619b4936128a0b 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 30181c1d9b820596cbaedcc70a3b5b1ad5644556..ded5b23cdb66c0de43dd78d87b7cab1315b5c588 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 1be7a68c157b843e2e07db8850c5bc3296000c93..83f188949ebd75f644914b810d74fb1c062126d6 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 fa7ab9d2070c2ec45433e33c140466fb707f4d82..3b2028b0902fcf40187375977e5a9412438abc17 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 e822f7fa422a86350c11bb93fd9141c45decfb0c..4c5f15013692b6dda44530987900d0f412dd2b94 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 0c3def8619d6ef814979da2dbb693555e3768373..6b7b557c1556d450415a4dc7bf10d71b3f9bf786 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 8710655d7f949493befa4353d2cd38fa3763f58f..b09ca9ab94f673547f2d5571ce421e3c9bd828f4 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 fcb388305e9dc3823b2724b4bf33dc1f5e951acf..9f9a8d9281a73396679b25f58622dae58215f12b 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 fe1b2e496a2abde35f5b9fa58f40294ff4449f4a..281309922a0bd18153732b435f6748b87d614e8c 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 6a56c3dfb1e9ed91bc7624a6bc5ddf39f7f8b052..fbc0f9661d5f84875d4c9e1b6a4983517a077435 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 9edcb8c60a755bce809926d789e06f7243f0f503..812b1a11bb9d5b3545fc7b2055ef010c7dfc2976 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 ca3ad28aa30de8a47f726cb62fec2663f805fc5e..273b26c9e55498d703c528cdd6855de216e81e46 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 86a8f1cac2f21794c9f4a3c33bf83cb505c08760..cdbd9b898c568de253a320b8e6733babfa492cab 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/contact/src/ContactFormEditForm.php b/core/modules/contact/src/ContactFormEditForm.php
index aa94540bb98c89f4b39b8bb5c2cb7cb8e47ec935..1df695337b20d1087f043acee30f7ca071d4dd4a 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 16d41b5acc482b77060d91745eecaa91d693deb8..c555f3bcec050c433c7fec0de587669dfd136f61 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/ContentModerationConfigureEntityTypesForm.php b/core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php
index 445216d96569a91e5fceb5dc76cb37a3b1ad6aeb..9b2585610070c5686d4e96586083fb35cb8fd7f0 100644
--- a/core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php
+++ b/core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php
@@ -17,6 +17,8 @@
 
 /**
  * The form for editing entity types associated with a workflow.
+ *
+ * @internal
  */
 class ContentModerationConfigureEntityTypesForm extends FormBase {
 
diff --git a/core/modules/content_moderation/src/Form/EntityModerationForm.php b/core/modules/content_moderation/src/Form/EntityModerationForm.php
index 6d768c86d8366d9f88268fbc32febc170422dd17..d0d3d0ef78f695cae18ca37d4d335e111c579cbe 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 9d225dc66b746c3edafabb0e6559db815f2de66a..bbbea44a167438953115a40845481fc42bfb1019 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 0f420f05687a1505974c0dcdf238098166603fe7..46344eba06543f2debf6ec2c1775d3c0dc3d76e9 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 c8de0fc68bb884bc614f3145e8054e0eed11e11d..21619d6fc2b4281aa39513b798ddac335f73628f 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 547032e67aaded7a3dc3d82d68297205b4a19f38..0e148d22f1103b3de8fca8f615cfdd86d23c9c4b 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 724f41307be0687beaea90d3ed9b04cc63f45d53..5f34e1078695241bba24c50e9a390a146970f177 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 949ffda667dfcd42209854429011af8642db67af..ed99a05e9752278f9440bb029a6c744f468b172c 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 c42a9d85a81ed508e46d980e382a6c1ca301ec99..883cc9e6e26553a01b5b6d988c8ad38fdd0e601d 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 92bfbde022d46b0985187af7834e384a774536b7..3fc50e4dbfb75b1f39b22d0408d4df5d81ef4c43 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/EntityDisplayModeAddForm.php b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
index ed1c5fe1e552e1743986ccca8b4e114008b54bd8..67450e55bc47e19f4de8920fce6f1cd2b076c0f3 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 f7d88046114840876def3617a55263445e7a61fc..1dc7633a68e3256ae0d216b84b0c9f1c864cdbc5 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 8a874dac5e2bd402b33c47965b03c977e8b40bb9..d7fa5527b1b058cba06199e0065db65949b39ff4 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/EntityFormDisplayEditForm.php b/core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php
index 2c3e3604605542a03316d23aa0ed2817ac6057da..128742f62117ab8904768dcc7ce9f7907c1805ec 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 9cecd83625171b5c17eacd24568a31e241732317..cfcc6fb900f89e145495fb0be51147dc6308ad67 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 c27f3d4f524e31f450ec883e8feb68c494110ae8..5e2a8cecd9c40fef6113728ba918ad80175834b3 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 67782311bc44ec5cd2cef4fc5a4fae048a6c6c1e..ab83e8fa351269d89529bf230c0c4503e6d19866 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 2895479b3667c4a36c5b3067863411b1189911af..34868add47965c6719192e0022eff96778a7f681 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 e1f278796e577dbdff111cc6cbbb375d03a68ce8..97e3ce7d102ee8924694b9c8f3cc92e3fb7c74c3 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 29f4367bb847f8af414b92ff3a5876cbd16e968c..0ae5084c0964f5469d5ac9872da307a1f8e677b1 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 9dc9d3595e6f33ccac03451610cdff3de2380d40..51353f6381b16fa9d7692af468f7d8a79cebb0fd 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 cb9b59881b911bbf71f54bcc7a88470cc924273c..39f1cb610b58fbdb1f8d836cc0c41194d43809b7 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 9ffd8c86c77a969db8737debba31f918ea3c3f47..8173a785c0a4d670839f347c6f426c0192625b20 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/Form/FilterDisableForm.php b/core/modules/filter/src/Form/FilterDisableForm.php
index c6e82949fd7e0e7d125aff913c36aee32d4c381a..a8a2ba3aad44600b6a819947c8848da27f75e17a 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 a5049a1635edc8561401d1727f6040e11b760fe3..12e9b97ee9659f05280203c11e918ea03454238d 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 0b011245743192d2bc99a61ff37a599cf8a6255a..afcb1ccc3366455b9b74eb946877da7ac68aa5a3 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 5b3666a843bd5cde9ae006c2659f476c5a4401dd..c65241019ab5b38417dc61fc6fc89e5819a87e82 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 9e5895d0dbe60c0ae709c291a96b7f6613ebaf3f..c894d3fbb30094fb0eb7e620e291469a1e70dc88 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 801888aabfa7c40d59affcc7809e494279aab654..a51446b173119a4b45ed189d7a1061ae1febe14c 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 12bb551ffa054e2b9f0c72a0d6f8d8f570c24666..f017f21b3962d642a622d20aed94a75cf9f664a7 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 ce304511b1f916ba6e5a10e36843ac1e933046ee..76f164caf6ca8583a7f83e32ea44e5c907c72b60 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 52cde33c694a0e22c9a6bb549d7a365cff7ee39c..e45f7a562f8f49cbbe0fceae4cd82ca6b45400cb 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 390e4dc7b35de5d4dc098d94d411af113e4365ac..0dd362c70cdd57ea3c31647c561efbc431b6f622 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/ImageStyleAddForm.php b/core/modules/image/src/Form/ImageStyleAddForm.php
index 41261cac39606f1ee8520ad6dac2e99d48a3570a..e0f5654a5d8a2f37e103158331eb94c982fa9588 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 c02c803f6e2b980793c5317a8754d5f68f862cf4..f49d6b867e253332cfe4d0962187fe0dd6350a4d 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 53d40da232b103e27f52f46f9aac24fc190f2b52..e7cfd50c586cc5ed5488e728d03d24716bf26f4c 100644
--- a/core/modules/image/src/Form/ImageStyleEditForm.php
+++ b/core/modules/image/src/Form/ImageStyleEditForm.php
@@ -12,6 +12,8 @@
 
 /**
  * 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 1326f888f67cb59f994a3d57a263b026216be613..df1d24e9ada4095b4023242b764539ff6eb8b28b 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/language/src/Form/ContentLanguageSettingsForm.php b/core/modules/language/src/Form/ContentLanguageSettingsForm.php
index 38aaffabd55616ca3512346e83840174058e8635..619d9440a3c5e6038b3838f0e5166426447123bd 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 5b9f15c2e25af501a954531d36ca4809cb3dfa41..12484079ecd8cf2bff203720ea8ce319398afff2 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 6113c1fe6b0facbba6fcb24d2086e834bb32e88f..6d4107a488c130a668bc97cadb89f2669fce1ac2 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 234994dbb4994b0e0283c86ef82a5b270bbc193e..7930fbd14b81d1d85f252ed8352c8caad9c7ff52 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/NegotiationBrowserDeleteForm.php b/core/modules/language/src/Form/NegotiationBrowserDeleteForm.php
index 1a409462fd4e226acd54ac608f67902ad122db7f..629fd086911ae5db4a5da6748d0b2831ee5ca3c8 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 be2edef9e8a16fe5312e5171fd9f255027a29356..798d4b06b0cd3a4b7ec32ad9ec5735beff3beb33 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 c1333e6a27a8b6874e218e824744449d1c0dfda3..e029134bb73fce67b50bba504a87c5e19eec3ea3 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 d4f1191862bd640b3b0eef3274fdd427c9803828..680dddfc0dacd0ad68ba6742f114eae611400b5b 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 b7ec4508f54143b39f0bf1be0144241cf62bb763..f2541c14546752584399e8a2a9083a52071be235 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 6f44f60203314ec6993d6cbdc2abeca8fd9cc2d2..89ba536094653d6469ccace29abab8310eb59781 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 4021667055dbcc74c67007a116d20551ea5beda9..33416df39d7a707168c8fb7de9ad18f331b5ea9d 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 f0fe8c51e5a09a8f187e561d8de078846f97a0e5..f0eb60e28e701204803ba9930ed6ff5b7017c470 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 7c6f9321dc7c108c883811f1162b78dcd4a4bbde..fc5b05d72aa72ea280ebe2d91ea9413129f12810 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 662fb1981694eafecfb8ca027c73813ffc8748c1..a9f15f07f18de6160e565e500965bfcf795cf126 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 e722cfb2b4f2548e47ff80c7eaf87c0480bf12f9..78945ebc2388fc99ef3d5e1958520f13e9cd2d69 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 d629009cf85b2fb3b618c28635446e97a4b54241..79656f2ed8e9559a1a2849130424bd106388cadc 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 aeef26f8ffb58406cf688f2a4e278955689eba4e..cfa3b696e8e7800db7a8c6aac3d294f695bcf98d 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/TranslationStatusForm.php b/core/modules/locale/src/Form/TranslationStatusForm.php
index cbf4d4a55ea47dc48804ba0cbd90a2217806439c..418fc78685ddd65dcd5490fef290192262970821 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/media/src/Form/MediaDeleteMultipleConfirmForm.php b/core/modules/media/src/Form/MediaDeleteMultipleConfirmForm.php
index 466abb26a351548720860364b4353252459ec04b..616a567e3c185522a557a77328dd48c3905219d9 100644
--- a/core/modules/media/src/Form/MediaDeleteMultipleConfirmForm.php
+++ b/core/modules/media/src/Form/MediaDeleteMultipleConfirmForm.php
@@ -12,6 +12,8 @@
 
 /**
  * Provides a confirmation form to delete multiple media items at once.
+ *
+ * @internal
  */
 class MediaDeleteMultipleConfirmForm extends ConfirmFormBase {
 
diff --git a/core/modules/media/src/Form/MediaTypeDeleteConfirmForm.php b/core/modules/media/src/Form/MediaTypeDeleteConfirmForm.php
index a181858b86309acd7a8372ad626ef947efd94107..f2ead198ec264708ccb842181410089deecc104e 100644
--- a/core/modules/media/src/Form/MediaTypeDeleteConfirmForm.php
+++ b/core/modules/media/src/Form/MediaTypeDeleteConfirmForm.php
@@ -9,6 +9,8 @@
 
 /**
  * Provides a form for media type deletion.
+ *
+ * @internal
  */
 class MediaTypeDeleteConfirmForm extends EntityDeleteForm {
 
diff --git a/core/modules/media/src/MediaForm.php b/core/modules/media/src/MediaForm.php
index 33c0d32c6f3045d29a098ef29394929b935cc35d..dd6b3fd2ad8b36dd8a54fe786c0aee5ba207a9d2 100644
--- a/core/modules/media/src/MediaForm.php
+++ b/core/modules/media/src/MediaForm.php
@@ -7,6 +7,8 @@
 
 /**
  * Form controller for the media edit forms.
+ *
+ * @internal
  */
 class MediaForm extends ContentEntityForm {
 
diff --git a/core/modules/media/src/MediaTypeForm.php b/core/modules/media/src/MediaTypeForm.php
index 80f7d211617dfa2a87a64bd381f80d9650116a89..5f301d58ed0b00c18ea8a1bc39b16f59a5c49c4c 100644
--- a/core/modules/media/src/MediaTypeForm.php
+++ b/core/modules/media/src/MediaTypeForm.php
@@ -15,6 +15,8 @@
 
 /**
  * Form controller for media type forms.
+ *
+ * @internal
  */
 class MediaTypeForm extends EntityForm {
 
diff --git a/core/modules/menu_link_content/src/Form/MenuLinkContentDeleteForm.php b/core/modules/menu_link_content/src/Form/MenuLinkContentDeleteForm.php
index 2b780c9e029adc42c77d6155d5c15e5b4c20d2b4..e9f953850bd62cc304961c473f08da0e07c4f635 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 4bdd6b9cfe0300dd9f7fe530a5694e752672a362..7175c1bb25cd21c0a2ef1ad6d68ef0acd72b7fe7 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 1cebd9091c2f41af3bb4ce834e0780b0778d6ae3..1b057a61afe90deecfa5fff755cb8600acf1e6a0 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 2dbd6a5e8adb5ec94ad0d81075e8f3793bd26b70..6cb50da1c484726d3a517c126671698df831da28 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 e37b16b0721703d9c5d2405d6c4c19e239dd5491..de9dccb9ed992f96462e4c67519ada80ffb00d69 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 cb27b25d773966138892a49aecd873be87ef7ad6..aec2c49eb0aee27e54c8eba908937a1c940ccc5b 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 1aed7197c3ba0fcf7fc9bac8921d65683fb62a57..d747e0ac2c9d423ff8defaa98ff2c41ccd9dadcc 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 91d8ad4a9ea15747111aa40e9b7dda5f46ee5853..8bc8f0685d7e737527dacda54036e043fe4010f2 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 da8c2025c11c7186815dc192b9f992ad1c1bba63..3f47a0c5fe6ed73af6f4c3c85d6a9cd4d311ab35 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 8b6125b87a8449bf62cb5c3f1f669b809ebdd84e..b06a65712fd42c06d67439e2d06e2aa990cbae07 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 86e5b59c125b7c687a8b316bc8fe033c4700e9c1..47e77990ccab874d3b7dccbdf511f5e1e6ce0fdc 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 8137c3f4fa1d7a4eb1733680ecfa27e1ca772652..fc6fe023f573f6dd7cd1b065f02ff36555ed6695 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 d5da697abeb860677014ec6b906da54fbd54eeff..0c68d8b254e9d8ec0e0030933f4f4864c8f57429 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 e4bea83fcb500b2087ea0ddac8506b162e202383..8234fcd1c9cc82ada65f79cf9da7970aca301a8a 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 b895c4c0c90532e8ee74312f9037bdf352388100..f479d29ea40384ba8383b67006e40474cbd59d72 100644
--- a/core/modules/node/src/Form/RebuildPermissionsForm.php
+++ b/core/modules/node/src/Form/RebuildPermissionsForm.php
@@ -6,6 +6,11 @@
 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 552e3fb6bad71d5b0307413726e11eb1e2f057ba..0513d1f7585f1fda933e7a91c2b44debd0f52ea7 100644
--- a/core/modules/node/src/NodeForm.php
+++ b/core/modules/node/src/NodeForm.php
@@ -13,6 +13,8 @@
 
 /**
  * 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 abef502e1e546673ec4c01df79f1368b8fa63e8f..9eec40c700879a7cf55ac33ec4898c6556c2d07f 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 b712ca0c082b4b645b3ddd8d8f642bf238e1d713..46ed439aa4d93f8f5f5baa70cc4b7dc1a0cf6d45 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 8f8d4f6b143d327eb8333cd462891f5569318048..59db6f9c19af1a2655980df2b639f89d6005cf50 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 ae9257a7e7ddd9b5434da1a4ba6dace055025514..d8be50d834c5fa2df067296c9f4495dd977be1d8 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 7d4a3693022c8fbf1298e9fdfe845896fb2c6264..9638b57ab516b340c76a6fca0c8f7902f07a6a2e 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 f7829061ecb3b87de66f4a784cdb9dfe094e846d..98bd95263606fde4cda9a157d839b40c9faaa099 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/quickedit/src/Form/QuickEditFieldForm.php b/core/modules/quickedit/src/Form/QuickEditFieldForm.php
index ba2dac38eb1fa88e976ff943926ebb70d2907444..31cc00463a1fbfc0ac7fd42d32ea16b3d28aa7e7 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 8ad0e6a6c872db725cd1a1584acc7d9b64f67824..424047390053001ba34b68d604666f26e6e59ec8 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 9cd4a15a265d4ebd7e7cb2533f50620d874e067a..2a30cb5b7bae0809e4715ef86b60a4f94564d143 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 7a9405fd7302a35ee18b780644cfeddfcc40e30e..612f8f62795109c3225f972bf383b3096ec93870 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 d5bc7850ec76d4e8895fc033607665417ff29571..6f5c142d6e41ddd5ca5029d7a0ad8127d4a13274 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 9d082eb5520a1b035ae509aa8e198861d21d304d..afbcfbc360ee7bdd8542eaa0cb51825a1fe27cb1 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 e46195baeaa2b877f03090e58dac4b77debb4589..0d8a34e2ea3b2bce050c148879c54a3b33de7240 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/tests/modules/search_embedded_form/src/Form/SearchEmbeddedForm.php b/core/modules/search/tests/modules/search_embedded_form/src/Form/SearchEmbeddedForm.php
index 64d9418fb5b8d1b743d06267bab145599f74b016..b1e26ca53ffb66342e315213d80fb40423776053 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 6c97577829365240f8da14f8223e4fca1f8fc07d..20094aa2c304730daeaf62fb890724fa7d8ff442 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 fcabeec7ec2aebd24530a3a63785992d91184907..0e6c32c4ffec7056f3dd699ed8299ad6ce4014e8 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 c383627b878ccd9b108722df55ed6472baea9f73..b14e4e386eb5148f883209220f546d9dd1dec10e 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 649cef765b7279aef4c9f7cb518554f07c66ef4b..726af172cde2480f448a8b0ee57b46f342c05e87 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 bfe3133e47d07d8a3d62e7f46044d662059e31b1..fa62cdb685f9ebe3fb4a1099146331221033c6ff 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 721d2517d417d113c4e2d4ab0b5dd7720b5773ea..3c8f4a798a69ceb7f95bdf08fb7cb094e17a0023 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 e1d21ae7c8008a9b89a626f42d6994ae65e59a99..55a9ca4e87badef1556b2beafaa857aa5055376e 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 d1ee436c80598af9a4ffad54bf9aa931e1c8bc12..20d2425a29fe9449916a3664d9182e0dc44246fb 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 1bf43ce4395255564e8630d55aa0fa93e604b989..0b704f90c54310afed47bde78ddef7c924995d38 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/statistics/src/StatisticsSettingsForm.php b/core/modules/statistics/src/StatisticsSettingsForm.php
index 4c06e0b1de5ca8e5a9f8280b2bed573b64859481..85c455bfae335b213e667ba39ce0333fc55bebd0 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 3957060e109a0414d4fe281480e3565168d583c7..228dc0b4a4b90519423fbda9a8b1806cc3aa2345 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 {
 
diff --git a/core/modules/system/src/Form/DateFormatAddForm.php b/core/modules/system/src/Form/DateFormatAddForm.php
index 957f9671e0ea4f01d18a4c1c941ff707ba0657a5..e30fbfc7813c73c5374404bb182ae373a4e48cbc 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 3d3047e71e19f8ebebb600232d050a1c5d660caa..155803282500ce5dfaf1ba91fec28e2ba04bf209 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 c63c0d7ac9f1b34c171acb4af97f41bffcc8283f..d6ad88e8eab18cbf1aff46a7707a3705cd2e09c8 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/FileSystemForm.php b/core/modules/system/src/Form/FileSystemForm.php
index d3a6caed0a644fbb3a752595b92ec7f1b77a3d9a..b0ca6d129eff360ca7b276f095e6d49cf954372a 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 0e70b47a3b50f7dd97a19915b4ca707529dddff0..8684c773123fb3032a9776c049a1fe1a3fc2938f 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 a305a4ff1d53bda8a8d471d8f83dd6243fd67722..b6446dfb61bd64174883be01874dfd30a5379ba8 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 50026606d2921022a0f5732de0f6a43232e7469e..912a4327fd982b6968dc2ff94f61ebb3d721c060 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 7488544cb60f957bea13ba73c0abeb47a5b6baf8..5586ce70ba7e594c3b8e5d00a0e108425bc1635b 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 28ff7ef4cc2101785a4f6294fe8ade5139f1fca5..43969d4380c9f000f9a06ff4f371332a6ce88631 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 c72f240acc791906fc4d00aec4f73d2d77f84137..f55f0d69ec5a5b84329560cf6b4910bd4d59ef9a 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 80348c59f13a798bbe08680260050b604deb5faa..7949067925d849b1f88b644a771bfcb010a125c1 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 33f99dbce6be710354540d0e0f32c722c7f80130..2ec5043589050bc49580b2261dbb6648a9bacf5b 100644
--- a/core/modules/system/src/Form/PerformanceForm.php
+++ b/core/modules/system/src/Form/PerformanceForm.php
@@ -11,6 +11,8 @@
 
 /**
  * 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 858364fe407993efbb016559a05b190ebfe1a5de..fb73b997946623f3bc1000d53379578bfd438fed 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 a66b26b104224c49600a2eaab188857c855feefc..9ade9380124b10a8df9508e7c899aeb032093760 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 986ff114971202911d9bb3ba953d0ab00bf24d47..d7508e63fcea93714853d573e013839b206ce73b 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 86376e2cdf1938bf26b6e051e9de2bd15ecd871c..4e4e1571fd54946ab0e81394055f30d8e6b14704 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 fb509aafe6d98ff1b087a7b7b913513ff0f1465e..58b1f1a9d62c1c36236f7702b3f5c475f29982c3 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 e8d17edd257d3c1e24f523139cbddeef9617ad75..1c85a788964d9fcd057a6824b291700a750ab5b7 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 393e3174aeab79b81cd6779df46b64a2c87bdce8..5717e6c3c4937dfce793c2bf5b3ccd3af404d374 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/AjaxFormsTestAjaxElementsForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestAjaxElementsForm.php
index 0290f8195c97a33085464c3d09d5e6c18721bf71..41a9b6d92ab0a4bc447f1a0e4b4ad5d1c2af036c 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestAjaxElementsForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestAjaxElementsForm.php
@@ -9,6 +9,8 @@
 /**
  * Form builder: Builds a form that has each FAPI elements triggering a simple
  * Ajax callback.
+ *
+ * @internal
  */
 class AjaxFormsTestAjaxElementsForm extends FormBase {
 
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 e3c09af92cd189182712764d39e21838a62f37ca..c7861e6adab121703c8700d9630b5c2f910b62eb 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/AjaxFormsTestImageButtonForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestImageButtonForm.php
index 20754ffd991d26d6f6389b05f586f6f7f8dc257c..316742b89edf0a9f4548b4473eae20824dd5791c 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestImageButtonForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestImageButtonForm.php
@@ -8,6 +8,8 @@
 
 /**
  * Form builder: Builds a form that has image button with an ajax callback.
+ *
+ * @internal
  */
 class AjaxFormsTestImageButtonForm 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 852cf4435214dd02434f1e7434b5c169fcce832f..7dddf877c4cb83a20f368f9a415da2dd24a18435 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 b8e9213e273b1b75ef6eaebd9e5823214262b0a5..6fc2857e3f2c5dec143ebfb2a25bd24b1b2504f6 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 fb3019493c0defac95f5a56ceefe6b6da3aa23a1..d908e3809cdfc24df6ba0fc9e781a2105156a122 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 5f11b6b71a2c2226deec446e5577562f908eb189..daedcf17069fef52dd72c46bc739366ceeb15cd6 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 ea431efa5adc1cac029018a6f40fcfca62a2cbcd..76dd497480da715a51ed27f05384abf35da320a6 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 fe2d02c5f13164e0b4768090d60f30a8d2c90679..a30094f79b6202a8bb53939e7a4f58f1b1381487 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 2d26bcf4d58cfec0ba1e812f9e79eedd825ee565..3a185a051682171a74dd3b7e8ac995316f9505b2 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 916831e96b503e38d8f3f82c1a1adad526dd3c44..151b50b7b8647b321d12cefee412a752236cfb9b 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 999649dfc2d9e942ab8e3c8c3d287ef388943381..f00d610d165683efe9936da9b1b7c5b34a0baa72 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 12eebccab638a4d9cb8bc31768034c1b60b8b3e8..63e2476319b60d78445ba6377f9591ef1c10342e 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 0c24456ee23910a2ee4a37eef5d652f090004a9b..3896cac3ac625ffb85fca9389b7c915fe1116cfe 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 e4c51143c85a3f0947a669a23c63cf0f9445afcf..75ff8ad9bf5d931efa1a58ee980688f4f71a01f2 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 eaa0f2037eeff8554b990d55ed37b8562f635015..ad830f601e770997beffc6ce39d77a010ab074ec 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 917f9e0ef6d471dc3b719026a74176faaaa70cf8..c5d4cef94d53673e64c323ad81d08e4f2cc07610 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 e3a40386a258384bf49f3a3c1e2a7ea170e40802..8ffbc52f5ed02fe709c97e370127d860189ed322 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 4e3de3bb4768cee8393df9c5be8b65c89f31066d..f8c082085bbddb04bd0b87cc71790631cd322e0a 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 62220cc61a1a85aa982fbeeeeb521e2728afa52d..dbbeb4733f61b52bced0b7184e6a99abb8f8f9bb 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
@@ -6,6 +6,11 @@
 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 ad0a86e8c81f9a2ecf01a2efe84c5bef9ee6717f..770170aee1b60b9191016a511e1eec10acd83a7b 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 a1a45a0abb7c2d9a4d00735d70f04740597905ed..95b14abbac1b5d4ab49ca1af6862881c7a5fa3b6 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 59f81e95bda5f9a774eebc6079ec136dd56aeb9b..6d9f1b7fc53a457b98c842c834747c1b1d6a6198 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 adab5bda00170141c2b7bd458cd61cf8a1522456..e95244c478d344301ca90a697d5e0247cccbeffe 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 07638809e352657e07ab7806fe6bebca9fbecf5b..ce092efd133c5271af5c6c4ceee3f670b3f71d88 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 81120ad1459cf174dcf72a9b77625210c3de7dd5..9da975668b2f9b694236f601a73ec38a9dc0faa5 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 594967950f115c816c2b52855c8078cef20ea142..839b909a75115939e8612942dd2868a4d68dbfa5 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 56e6d2ee0fb6e9c3a4795f0a1333af31239b5618..5d367795df267e48a8375c9e8a52b17d34afa11d 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 8e82623dbceeaa338ecbad3c2e7afb26ea929db9..8b01c32b561daa2895ff316b364896d5c628eafa 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 14dcb0c3374a4f85170dbd21ce6db5ea60645c98..acc1b115b4e4cf390632197268bb4f202d57e949 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 f910469bda4b55f23c0bf1ab25db8cd9faad0a67..4a7c00251e34132e42a4bd0c5099f54934e157f6 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 d5e0fd965872d285f729b7ff9c294402a5109f54..211cd7f73d4d5902188a1f8756c581ae2f9bc73b 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 5c3decd17f3770bd2538b00ba44a04a0cc918b8e..a032771e9c41d478bec9dcbf2e683d83344bab36 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 b141b7cc2799f6f7524c9118a3fad3c0c419652d..44614016bf540b7946b4b178ee1cae6edffe0b40 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 002b07dd7f7361ea280c21211eb6336bd7f1ebc2..12a05e12d2b1b84f6c57222b71bde4c8bd98cd57 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 37ef246ec8f3af9efe61cf2f096e49fe447117af..b37d6bba44b45bd91420a0ef565e457f0511b0a2 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 2d2f98bdf46db47f65654de8962a3b86cf49f04a..7a29d7d7ee000c0136ad61253da23cc3029f6282 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 8cdac632d09f1666fc681ac1591b5a3954f32795..67d71b361e1f081ba036a9084ed6a4b925cbdd54 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
@@ -6,6 +6,11 @@
 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 74c92ab611189480759c6f7bc214cb874a5c0a52..88de2300898a59bff9dbbe1a2192276ccfe3fe4a 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 ba41e19fef8b6f7e5ca3ce523ab0e14d5bbf6073..dc0ff1b47b5d2ed93d4c43b175ccd93037ddc6f4 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 deff0b49d4733724bac6fab2683d378618d23d4a..883602217373310fcdf5ce48a0f28354c348d5b8 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 542edc8a76f1ebc9ef668db82628949446c19178..ee287f4ced36c51c0494f16d95dc341027a1fef7 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 ab281462eb679540e49355ea4c1d03fe32f731ef..0965f9dec311a26cb7cd50d620a0673cfa720f52 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/FormTestOptionalContainerForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestOptionalContainerForm.php
index 7cacf2e20c7efd9d87f137b46f81d00296869281..063f03a461c6bd8c44e3a7eb04ce3a464180619f 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestOptionalContainerForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestOptionalContainerForm.php
@@ -7,6 +7,8 @@
 
 /**
  * Builds a simple form to test the #optional property on #type 'container'.
+ *
+ * @internal
  */
 class FormTestOptionalContainerForm 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 9180628b1395b52ca88ad0b9ddd2f38800ec6240..19157f5d4b498812c35b25c41bb8fa9128d31272 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 9dd53219f13a9f23c610797bb5222c95a457b565..af43a2030d0d3ad8d55a7214dd7d13950d6790b4 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 66928f04f2aba8be6d1bdb3416dc17d99999a248..43d79031df0a53606b8c3e37bb96eb896f63b70d 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/FormTestRadiosCheckedForm.php b/core/modules/system/tests/modules/form_test/src/Form/FormTestRadiosCheckedForm.php
index efb1d4d42110e61293b74b5708508849f19282c8..879dccd03df3c05092ff2d446493da76239e6b7a 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/FormTestRadiosCheckedForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/FormTestRadiosCheckedForm.php
@@ -8,6 +8,8 @@
 
 /**
  * Form constructor to test #default_value settings of radios.
+ *
+ * @internal
  */
 class FormTestRadiosCheckedForm 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 94240e5e9a9c21174a42da2489ba07117638ce7b..11916646ff5f8235c0def53a3f35b3ca90dc6250 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 541520585d67544bf027fc70b96a7b65b176edf3..23c086299aedc4024f1b8468b82fd095e8b6687c 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 58934a7819995f9f54e73d964420ba672bb3f0ca..662de8f7d4824737c854910cd35b23a37afbde73 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 4768acf901f5f549afddff75425ce779056a8438..69b20a854de1f9059be11fd1d545a2a426392d15 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 b0aa1b00b7e6a2d707a64bf3659d6c2bb3cff4d5..6c6ff3a4fa6b606bb688abeee0b689fa844934ce 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 0ab3a0d211bc9aca3d4fbdc161d0062bde0c19a1..a8b581b12d3c7de46590bcd9904db14fdca0f545 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 a922d2a86f8886c50647f333825e334ba47ca2f2..d1b14d8d0e8789d67ef588ef816b5f46dcaa2447 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 e34af83b1692de9f65b04cb14e11f3b3c43146fc..af7f51cf898129c92d95c6da796939deef932fc7 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 9187012977c291aa310545d11c2ccd06f4673123..f81658d537d79d9f129849f8f016f499c267c4d6 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 f27e5e066e790c776d908e05b47b8745e8263cd6..2554d89686add44edfb9e0535e33d47aa0310936 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 758d5afe0d0ea9b2d2192d1a952288732978125b..8196d4d6f6841d4fa571c348ede84423b3564aeb 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 1c9628bcf30b28e5d99eafe48b7b2a38733053fb..becce376f2823c3c2705f8b22dd9035dcac261cb 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 199a7d3e274bd74fe76b9de235c863c2a6afb4d1..bac78eb41df2ab7ab27f894381a23ccb1bac2850 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 9a1dc2e6c24b71215eebb9f2e711c0c1332c2b6c..af41782cb3e1c2f10cbf805f421980321abba67f 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 d6d606aea20d06900f8068885d27393303b6dea1..aec320e9e1b81a2eb83f897155dfc13182da3c7e 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 f21ae3c6f47e65301b0c0e5abc1424dcc990b455..d79b235e0f29febd0817124b11b613b64e5a5776 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 d4a0c1d40792b5fb9aacf38fd21d62f38339d9e1..1d46d7cc65968c32c07a50188c67bbcde0db5f51 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 fff0e80521b649f916d8f030394b28e16ef00906..6ce12b45aba058bebb14e1e44017ca33c7ac29db 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 41772da288d241ec860250b0779a57b06e79ce57..7123aceef1a8736375a82551075a5c0a93eef792 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 1e996eea3b13f3e5bb0456b0b9fb69cb887f3118..c4b568edd085ebe2c2518c85fafa66611f4c81de 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 88e6b3531853f18420d50f9b612706f9a8945d70..13aec600abe15f38d43f3bf5b3b0c44c2e1d8c39 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 29b3b5f96134e12f10d34f932b604481fcd55a81..1829ab25662be1059e793c19e2d75328a457ed82 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 cb171a66712f02678d591a50ec4ed232bf38c170..1b343fccc932d32d3bf3dfdb2af1a7d0e4f879c3 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 b89636a433aba796cb7c8ef27a6802f9ab96b96b..fbd7160a100ea6ef6b47564e6cef8ddf26a758da 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 163ac22706852e198b2d761974703d5c8b666b08..842abd70e982af76be1c1a262cdbcdc8bd542465 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 7531ca816a519b5cd5c3d19c7c26de56bf63ed21..0d86a2d7aed4cd29ce108c74f9f4087e27ec52e6 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 019513d082fb2bf52c4a4d5e0dd29d910e3530b7..bde049e10e47a768de8555b67dc02e1b9d8ebf67 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 7573253481e3aabd3a517a11d16680cdd83ab560..40d474d7aa1c8710c6b9d1801ed7dc4bbe96be84 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 f99fbe73004e68a16d2336d18e5f51a3ecd3d271..d7fd119c750a2ba2c592f86c8b437a7560acdc6e 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 effd319bb0c575fee87679bd5b97a9f5262f272a..c1d8555552d9e89582ecd688f811fd15c7f1a152 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 f393beac0000aafd182cb4b8381a109f9bb4a82a..0a2855b8d182fd56e34778a58b902d2d9938be07 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 087378b89a6d3985c9204d6fc4a54d4bdbe7a99f..d46db774d68fb969e5e34147a334858b9314e620 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 bf250ac4524f68193ce84a5d48438302aa19e979..c09237ac6bdbc4e4d5db592fa67c998851563236 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 55b1b18678628680e5358fa7eb17807a0e05f394..4f4ad0a08b42407600eb0de2c73eaf41c64f4ce1 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/system/tests/src/Functional/Form/StubForm.php b/core/modules/system/tests/src/Functional/Form/StubForm.php
index 4cf91c04ce815d9a5fb635a05aa10721211012be..9e20c365ba83f4d8cae376d31a21fdd47cadf5cc 100644
--- a/core/modules/system/tests/src/Functional/Form/StubForm.php
+++ b/core/modules/system/tests/src/Functional/Form/StubForm.php
@@ -7,6 +7,8 @@
 
 /**
  * Provides a stub form for testing purposes.
+ *
+ * @internal
  */
 class StubForm extends FormBase {
 
diff --git a/core/modules/taxonomy/src/Form/OverviewTerms.php b/core/modules/taxonomy/src/Form/OverviewTerms.php
index d73598d67216ea1470ebeb01d15bda90299ce147..df80a47035be0b522cbfd9cdf0809726bb8db4cb 100644
--- a/core/modules/taxonomy/src/Form/OverviewTerms.php
+++ b/core/modules/taxonomy/src/Form/OverviewTerms.php
@@ -14,6 +14,8 @@
 
 /**
  * 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 0e97ff64a4b0a4cba75a6bf87d943dfbcddfbd90..b50a5daf189bec0c2a01f03bc376f7df86a0135b 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 7c91b7868cbb0e3c378fadb396a339c07cada464..7bca948c71aaf4bf2f544bcf5894e631eeadc6f2 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 e036ff91768a8b77fa1a37025069e4126dc6c01d..439d994cf1046472562c2a3b73b788c602e2118c 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 1eae95a0d4f3bfcd32440d1c505b74732a93c981..bb0b10e8998fccc11b81161424c81cb2414299d5 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 63f0ccb8ab5f7100dee63c3b7348e64790d8eaae..23e911b9a8f6724cbc94a17f7f3eee2d5846ff6d 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 a99383ab953c4e748ef4428dd6019f6975191597..b1beb864b4319376e545813582d9223492b60a73 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 0b3196865c5ad266240f963c4725059ae594f306..e17d214bb7d7ed8ca45e604879b28194316243f6 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 ef9a2f17122ff2ee117559d8e552335d3c9ae86f..9dad0222133384a0880b4dd2d3715b31eb01b2a8 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 1860269d6092a1bd7093b4e480152c3096ce02df..ac8981cf49eb035aab1ea666100b7a9afae3a877 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/AccountSettingsForm.php b/core/modules/user/src/AccountSettingsForm.php
index eacc37857c7412aaa42a12f2ba9286beb5417cfb..bd80dd7e297bbed86a512ef92ffaafa329a45d78 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 14c553c3b78dea27ba9f353e01da0f74a072530a..da7a5f4f9df06e705f3850030eac4302de285872 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 25a54ec4b72371c49ee270429b2d7a3b17efb367..703e0ce96a5ed37c4c2271a126f7318385e86a30 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 62a64e5d2b0cc08ef2cd27926132c4a0649a1787..985d19918d3761163a1ec3e559f85f3a6f05ace4 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 972f8250b3dd4aec26463d7155998df93110b5e5..a7ae862bb57d7e07eac71de74c81d280412e625e 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 ce8c7cca1d713633143e8e2fbfe87ef279a21651..bf9538c025770f504014810058ad79419dee640e 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 26f26c92638e45dcd6d412106433fa1bbc50b547..daa879ab312d0cce08de1a4e00ee2edab2d4509a 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 b8caf7bbf47ab0e7f73479f3ac689010567df58c..c9794634a0a0b384f767a3729eba430fcf1a5d03 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 343d4d0e060c28e23eb3235e90610d1819788269..c856b75da9d40123fdffb670b50446b7175b1bc7 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 7a97974fb2ddf05514f6b39258dee21a32b7a7c0..4974e69d8d6028ae9f630da212b3459efce37117 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 7e7885354b9b2720d033b73c1111117f74d278f0..e40067cf83cdd18da7240259c4b04687ccbe9555 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 44e7ec4b0f3b7fddd7d2b515504fdace23e58617..459708a7bcc5fbcc317c60e7d81e90b2643af892 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 80d19d1faff6874a16163156b8c109a85e2b3239..03e95917ccf405f37d0e8356ecc723eb179b9c10 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 78aa998006675c9e0be613bedd57d74f85a9aaad..7269cbaf3a9d4ffd9d81a3fd39a16630e2bc83b6 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 36f34c26a1f4323bd17302fd2c76542c34cc343a..e4aa1c1f193d8bc9a7f13c26530557e6035e11ec 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 ec0c6554bd80de754382a36356a9411f0f5c103a..8b53772e8c007441b0879027892c5d0f4b241f75 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 52784d3d3c5443aece69e457d7762a42506ff582..0c630dfe0bbe1618425a55e33afbad66a8e4cf8e 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 972b4b940fd7966e851509683126458ee9c1730f..5d68f0bd508e0b75f5f338e071fd4f94e1dc85bb 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 a79d03142ebdaf1a4bee7f61efd55e20b1464ddf..8e71123389985a0fa6739bfdf8a4bc3883254934 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 b4d0f136b8828d8e752705cf1fa119dd3ef14286..b208139f5ee7194564daa9ac6443f3711f951971 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 302d75959eb221f85ddab8c2627d4d2822fb0559..3f75a306b1f7678ab25d2d7158ac53712ea5836f 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 07b1625a8d41168e9d00b72a666c6fabe812243c..fca2099f394543f22bb880ec851530e80e63d714 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 1ffb710ca1dcafe2b1ab6515f52aedcb13f50960..6f6834d09881b28b02502a8ae4d7a208a2a7e83a 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 32986810512d3cbc7b6a39e95c312b20df688748..67ddbe89257ea7d227bddceb8ab56932c1557346 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 377a3d55c236ab5ea82b21713e5c1ade4468ae69..c9ad4136412915993d147a966a9fac8fad0060cd 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/BasicSettingsForm.php b/core/modules/views_ui/src/Form/BasicSettingsForm.php
index bcd533662c59054b68d2ade3dec7b9ee98b8f22f..5b7bfd73a50e2cf2c6f4eb0ca262a4cf1e10cb05 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 b73e618cc2d2fc5175c4229ba2ecbb1d9097c36c..464920b7b58b0c9ab85856f6e5b32b7a7eb90426 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 429032c845776334d7979cedccd2d6126a7c043f..e76621f2b36cbb2dde2a1c395f40c18a6c130e7a 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 fa2db6080116d121a35845c26a59a0c51e7e0eed..9cfe341d95ebb1a5b156989799cdb319bbbe219c 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 1781e3312e4bec4d902f85c9f49a0202f829b9a3..cc8a77e957cb2750534ed2346a733d946efd61a2 100644
--- a/core/modules/views_ui/src/ViewEditForm.php
+++ b/core/modules/views_ui/src/ViewEditForm.php
@@ -19,6 +19,8 @@
 
 /**
  * Form controller for the Views edit form.
+ *
+ * @internal
  */
 class ViewEditForm extends ViewFormBase {
 
diff --git a/core/modules/views_ui/src/ViewPreviewForm.php b/core/modules/views_ui/src/ViewPreviewForm.php
index 2cc25332efc78f253b1f9cbd08f33f2909798d32..4bc8eaab3ad3dda49647de4a2eaa37a5314da0f8 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 19894691239b69d3c06c0c880afedeb55d14e3a0..e3aac6fc4a49f0adf320c949c09353d411b265b4 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 e122f4054346bb6f102aeec95d46baed30c7fc77..508205738db442f492ca7144c50d5da716c9a8e8 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 889b7bbfedbee10a84055a5d3b78d3b97bb5426d..578f25691d6796bb34d5ba38340a67d90e45e8b7 100644
--- a/core/modules/workflows/src/Form/WorkflowEditForm.php
+++ b/core/modules/workflows/src/Form/WorkflowEditForm.php
@@ -15,6 +15,8 @@
 
 /**
  * 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 ab7b3618bdf36b57f40090f731dfea8837222677..4b5f723395534174446cddc591100acba015f8fb 100644
--- a/core/modules/workflows/src/Form/WorkflowStateAddForm.php
+++ b/core/modules/workflows/src/Form/WorkflowStateAddForm.php
@@ -12,6 +12,8 @@
 
 /**
  * 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 bfca31e97ef8f6919c9808ffea5adf89b9a746bd..14d1bbe017b37ba48d8bd79b3df3a90a47ad37e1 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 940fb8c14faa946083bc059a10aafb03fe937171..bba3b11c13493d3cb2c484e846195c876fd6bda0 100644
--- a/core/modules/workflows/src/Form/WorkflowStateEditForm.php
+++ b/core/modules/workflows/src/Form/WorkflowStateEditForm.php
@@ -13,6 +13,8 @@
 
 /**
  * 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 9580e27808c39d4c620329a74393ea166efbbe14..1ac8de54b405c99defea09983d447bbcb9f9e990 100644
--- a/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php
+++ b/core/modules/workflows/src/Form/WorkflowTransitionAddForm.php
@@ -13,6 +13,8 @@
 
 /**
  * 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 27add727f62ec02ee27acc0b70ad677540bb2820..63479626d4f8756cd324ba21889cfcf6dfa2949e 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 63b2ab47995c455e4b7a32e2155476818ea2cde5..9d3a2231d630461ff6557dda346f88040f725fb9 100644
--- a/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php
+++ b/core/modules/workflows/src/Form/WorkflowTransitionEditForm.php
@@ -14,6 +14,8 @@
 
 /**
  * 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 d2e5eae318af654615c5782cbe3711af7fa31f4e..ee02caef0b6c378fd9be2a96aef60a9f811efd36 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 {