42 files declare their use of Plugin

Action.php in core/lib/Drupal/Core/Annotation/Action.php
AggregatorFetcher.php in core/modules/aggregator/src/Annotation/AggregatorFetcher.php
AggregatorParser.php in core/modules/aggregator/src/Annotation/AggregatorParser.php
AggregatorProcessor.php in core/modules/aggregator/src/Annotation/AggregatorProcessor.php
AnnotatedClassDiscoveryTest.php in core/tests/Drupal/Tests/Component/Annotation/AnnotatedClassDiscoveryTest.php
AnnotationBridgeDecoratorTest.php in core/tests/Drupal/Tests/Component/Annotation/Plugin/Discovery/AnnotationBridgeDecoratorTest.php
Archiver.php in core/lib/Drupal/Core/Archiver/Annotation/Archiver.php
Block.php in core/lib/Drupal/Core/Block/Annotation/Block.php
CKEditorPlugin.php in core/modules/ckeditor/src/Annotation/CKEditorPlugin.php
Condition.php in core/lib/Drupal/Core/Condition/Annotation/Condition.php
Constraint.php in core/lib/Drupal/Core/Validation/Annotation/Constraint.php
ContextDefinition.php in core/lib/Drupal/Core/Annotation/ContextDefinition.php
DataType.php in core/lib/Drupal/Core/TypedData/Annotation/DataType.php
DisplayVariant.php in core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php
Editor.php in core/modules/editor/src/Annotation/Editor.php
EntityReferenceSelection.php in core/lib/Drupal/Core/Entity/Annotation/EntityReferenceSelection.php
EntityType.php in core/lib/Drupal/Core/Entity/Annotation/EntityType.php
FieldFormatter.php in core/lib/Drupal/Core/Field/Annotation/FieldFormatter.php
FieldWidget.php in core/lib/Drupal/Core/Field/Annotation/FieldWidget.php
Filter.php in core/modules/filter/src/Annotation/Filter.php
HelpSection.php in core/modules/help/src/Annotation/HelpSection.php
ImageEffect.php in core/modules/image/src/Annotation/ImageEffect.php
ImageToolkit.php in core/lib/Drupal/Core/ImageToolkit/Annotation/ImageToolkit.php
ImageToolkitOperation.php in core/lib/Drupal/Core/ImageToolkit/Annotation/ImageToolkitOperation.php
InPlaceEditor.php in core/modules/quickedit/src/Annotation/InPlaceEditor.php
LanguageNegotiation.php in core/modules/language/src/Annotation/LanguageNegotiation.php
Layout.php in core/lib/Drupal/Core/Layout/Annotation/Layout.php
Mail.php in core/lib/Drupal/Core/Annotation/Mail.php
MediaSource.php in core/modules/media/src/Annotation/MediaSource.php
MigrateDestination.php in core/modules/migrate/src/Annotation/MigrateDestination.php
MigrateField.php in core/modules/migrate_drupal/src/Annotation/MigrateField.php
MigrateProcessPlugin.php in core/modules/migrate/src/Annotation/MigrateProcessPlugin.php
MigrateSource.php in core/modules/migrate/src/Annotation/MigrateSource.php
PluginExtended.php in core/modules/system/tests/modules/plugin_test_extended/src/Plugin/Annotation/PluginExtended.php
PluginTest.php in core/tests/Drupal/Tests/Component/Annotation/PluginTest.php
QueueWorker.php in core/lib/Drupal/Core/Annotation/QueueWorker.php
RestResource.php in core/modules/rest/src/Annotation/RestResource.php
SearchPlugin.php in core/modules/search/src/Annotation/SearchPlugin.php
SectionStorage.php in core/modules/layout_builder/src/Annotation/SectionStorage.php
Tip.php in core/modules/tour/src/Annotation/Tip.php
ViewsPluginAnnotationBase.php in core/modules/views/src/Annotation/ViewsPluginAnnotationBase.php
WorkflowType.php in core/modules/workflows/src/Annotation/WorkflowType.php

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