30 files declare their use of Markup

AssertHelperTraitTest.php in core/tests/Drupal/Tests/AssertHelperTraitTest.php
AttributeTest.php in core/tests/Drupal/Tests/Core/Template/AttributeTest.php
ConfigTest.php in core/tests/Drupal/Tests/Core/Config/ConfigTest.php
EngineTwigTest.php in core/modules/system/tests/src/Functional/Theme/EngineTwigTest.php
errors.inc in core/includes/errors.inc
Functions for error handling.
FieldPluginBaseTest.php in core/modules/views/tests/src/Unit/Plugin/field/FieldPluginBaseTest.php
Contains \Drupal\Tests\views\Unit\Plugin\field\FieldPluginBaseTest.
HtmlTag.php in core/lib/Drupal/Core/Render/Element/HtmlTag.php
HtmlTagTest.php in core/tests/Drupal/Tests/Core/Render/Element/HtmlTagTest.php
LinkGeneratorTest.php in core/tests/Drupal/Tests/Core/Utility/LinkGeneratorTest.php
MailManager.php in core/lib/Drupal/Core/Mail/MailManager.php
MailTest.php in core/modules/system/tests/src/Kernel/Mail/MailTest.php
Messenger.php in core/lib/Drupal/Core/Messenger/Messenger.php
MessengerTest.php in core/tests/Drupal/KernelTests/Core/Messenger/MessengerTest.php
PluginBaseTest.php in core/modules/views/tests/src/Kernel/Plugin/PluginBaseTest.php
Contains \Drupal\views\Tests\Plugin\PluginBaseTest.
RendererPlaceholdersTest.php in core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php
Contains \Drupal\Tests\Core\Render\RendererPlaceholdersTest.
RendererTest.php in core/tests/Drupal/Tests/Core/Render/RendererTest.php
Contains \Drupal\Tests\Core\Render\RendererTest.
SerializerTest.php in core/modules/jsonapi/tests/src/Kernel/Serializer/SerializerTest.php
system.install in core/modules/system/system.install
Install, update and uninstall functions for the system module.
SystemTestController.php in core/modules/system/tests/modules/system_test/src/Controller/SystemTestController.php
Test.php in core/modules/system/tests/modules/test_page_test/src/Controller/Test.php
TestController.php in core/modules/system/tests/modules/js_webassert_test/src/Controller/TestController.php
theme.inc in core/includes/theme.inc
The theme system, which controls the output of Drupal.
ThemeManager.php in core/lib/Drupal/Core/Theme/ThemeManager.php
ThemeRenderAndAutoescapeTest.php in core/tests/Drupal/KernelTests/Core/Theme/ThemeRenderAndAutoescapeTest.php
Contains \Drupal\KernelTests\Core\Theme\ThemeRenderAndAutoescapeTest.
TokenTest.php in core/tests/Drupal/Tests/Core/Utility/TokenTest.php
twig.engine in core/themes/engines/twig/twig.engine
Handles integration of Twig templates with the Drupal theme system.
TwigEnvironment.php in core/lib/Drupal/Core/Template/TwigEnvironment.php
TwigExtension.php in core/lib/Drupal/Core/Template/TwigExtension.php
TwigMarkupInterfaceTest.php in core/tests/Drupal/KernelTests/Core/Theme/TwigMarkupInterfaceTest.php
Contains \Drupal\KernelTests\Core\Theme\TwigMarkupInterfaceTest.
views.views.inc in core/modules/views/views.views.inc
Provide views data that isn't tied to any other module.

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