17 files declare their use of CKEditor5PluginDefinition

ckeditor5.api.php in core/modules/ckeditor5/ckeditor5.api.php
Documentation related to CKEditor 5.
CKEditor5.php in core/modules/ckeditor5/src/Plugin/Editor/CKEditor5.php
CKEditor5Plugin.php in core/modules/ckeditor5/src/Annotation/CKEditor5Plugin.php
CKEditor5PluginManagerTest.php in core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
ckeditor5_drupalelementstyle_test.module in core/modules/ckeditor5/tests/modules/ckeditor5_drupalelementstyle_test/ckeditor5_drupalelementstyle_test.module
ConfigurablePluginTest.php in core/modules/ckeditor5/tests/src/Kernel/ConfigurablePluginTest.php
EnabledConfigurablePluginsConstraintValidator.php in core/modules/ckeditor5/src/Plugin/Validation/Constraint/EnabledConfigurablePluginsConstraintValidator.php
FundamentalCompatibilityConstraintValidator.php in core/modules/ckeditor5/src/Plugin/Validation/Constraint/FundamentalCompatibilityConstraintValidator.php
Language.php in core/modules/ckeditor5/src/Plugin/CKEditor5Plugin/Language.php
LanguagePluginTest.php in core/modules/ckeditor5/tests/src/Unit/LanguagePluginTest.php
Media.php in core/modules/ckeditor5/src/Plugin/CKEditor5Plugin/Media.php
MediaLibrary.php in core/modules/ckeditor5/src/Plugin/CKEditor5Plugin/MediaLibrary.php
PluginManagerDependentValidatorTrait.php in core/modules/ckeditor5/src/Plugin/Validation/Constraint/PluginManagerDependentValidatorTrait.php
SmartDefaultSettings.php in core/modules/ckeditor5/src/SmartDefaultSettings.php
SmartDefaultSettingsTest.php in core/modules/ckeditor5/tests/src/Unit/SmartDefaultSettingsTest.php
StyleSensibleElementConstraintValidator.php in core/modules/ckeditor5/src/Plugin/Validation/Constraint/StyleSensibleElementConstraintValidator.php
ToolbarItemConditionsMetConstraintValidator.php in core/modules/ckeditor5/src/Plugin/Validation/Constraint/ToolbarItemConditionsMetConstraintValidator.php

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