24 files declare their use of BlockPluginInterface

block.api.php in core/modules/block/block.api.php
Hooks provided by the Block module.
BlockComponentRenderArray.php in core/modules/layout_builder/src/EventSubscriber/BlockComponentRenderArray.php
BlockComponentRenderArrayTest.php in core/modules/layout_builder/tests/src/Unit/BlockComponentRenderArrayTest.php
BlockEntitySettingTrayForm.php in core/modules/settings_tray/src/Block/BlockEntitySettingTrayForm.php
BlockForm.php in core/modules/block/src/BlockForm.php
BlockHooks.php in core/modules/block/src/Hook/BlockHooks.php
BlockInterfaceTest.php in core/modules/block/tests/src/Kernel/BlockInterfaceTest.php
BlockPluginHasSettingsTrayFormAccessCheck.php in core/modules/settings_tray/src/Access/BlockPluginHasSettingsTrayFormAccessCheck.php
BlockPluginHasSettingsTrayFormAccessCheckTest.php in core/modules/settings_tray/tests/src/Unit/Access/BlockPluginHasSettingsTrayFormAccessCheckTest.php
BlockSettings.php in core/modules/block/src/Plugin/migrate/process/BlockSettings.php
BlockStorageUnitTest.php in core/modules/block/tests/src/Kernel/BlockStorageUnitTest.php
BlockTestHooks.php in core/modules/block/tests/modules/block_test/src/Hook/BlockTestHooks.php
block_test.module in core/modules/block/tests/modules/block_test/block_test.module
Broken.php in core/lib/Drupal/Core/Block/Plugin/Block/Broken.php
ConfigureBlockFormBase.php in core/modules/layout_builder/src/Form/ConfigureBlockFormBase.php
ContextualTestHooks.php in core/modules/contextual/tests/modules/contextual_test/src/Hook/ContextualTestHooks.php
contextual_test.module in core/modules/contextual/tests/modules/contextual_test/contextual_test.module
HelpHooks.php in core/modules/help/src/Hook/HelpHooks.php
MenuUiHooks.php in core/modules/menu_ui/src/Hook/MenuUiHooks.php
NavigationHooks.php in core/modules/navigation/src/Hook/NavigationHooks.php
NavigationRenderer.php in core/modules/navigation/src/NavigationRenderer.php
SectionComponentTest.php in core/modules/layout_builder/tests/src/Unit/SectionComponentTest.php
SectionRenderTest.php in core/modules/layout_builder/tests/src/Unit/SectionRenderTest.php
SystemHooks.php in core/modules/system/src/Hook/SystemHooks.php

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