11 files declare their use of Tags

EntityAutocomplete.php in core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php
EntityAutocompleteController.php in core/modules/system/src/Controller/EntityAutocompleteController.php
EntityAutocompleteMatcher.php in core/lib/Drupal/Core/Entity/EntityAutocompleteMatcher.php
EntityAutocompleteTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityAutocompleteTest.php
TagsTest.php in core/tests/Drupal/Tests/Core/Common/TagsTest.php
taxonomy.module in core/modules/taxonomy/taxonomy.module
Enables the organization of content into categories.
TermTest.php in core/modules/taxonomy/tests/src/Functional/TermTest.php
UnpublishByKeywordComment.php in core/modules/comment/src/Plugin/Action/UnpublishByKeywordComment.php
UnpublishByKeywordNode.php in core/modules/node/src/Plugin/Action/UnpublishByKeywordNode.php
ViewExecutable.php in core/modules/views/src/ViewExecutable.php
ViewsUIController.php in core/modules/views_ui/src/Controller/ViewsUIController.php

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