22 files declare their use of RfcLogLevel

AreaDisplayLinkTest.php in core/modules/views/tests/src/Kernel/Handler/AreaDisplayLinkTest.php
BigPipeTest.php in core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
bootstrap.inc in core/includes/bootstrap.inc
Functions that need to be loaded on every Drupal request.
CronQueueTest.php in core/modules/system/tests/src/Kernel/System/CronQueueTest.php
dblog.admin.inc in core/modules/dblog/dblog.admin.inc
Administrative page callbacks for the Database Logging module.
DbLogController.php in core/modules/dblog/src/Controller/DbLogController.php
DbLogTest.php in core/modules/dblog/tests/src/Functional/DbLogTest.php
EntityReferenceSettingsTest.php in core/modules/field/tests/src/Kernel/EntityReference/EntityReferenceSettingsTest.php
errors.inc in core/includes/errors.inc
Functions for error handling.
ExceptionLoggingSubscriberTest.php in core/tests/Drupal/KernelTests/Core/EventSubscriber/ExceptionLoggingSubscriberTest.php
FakeLogEntries.php in core/modules/dblog/tests/src/Functional/FakeLogEntries.php
HandlerFilterRolesTest.php in core/modules/user/tests/src/Kernel/Views/HandlerFilterRolesTest.php
InstallerExistingConfigMultilingualTest.php in core/tests/Drupal/FunctionalTests/Installer/InstallerExistingConfigMultilingualTest.php
LegacyBootstrapTest.php in core/tests/Drupal/KernelTests/Core/Bootstrap/LegacyBootstrapTest.php
MigrateMessage.php in core/modules/migrate/src/MigrateMessage.php
MigrateUpgradeExecuteTestBase.php in core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeExecuteTestBase.php
ModuleTestBase.php in core/modules/system/tests/src/Functional/Module/ModuleTestBase.php
responsive_image.module in core/modules/responsive_image/responsive_image.module
Responsive image display formatter for image fields.
SecurityAdvisoriesFetcherTest.php in core/modules/system/tests/src/Kernel/SecurityAdvisories/SecurityAdvisoriesFetcherTest.php
UpdatePathTest.php in core/modules/dblog/tests/src/Functional/UpdatePathTest.php
ViewsIntegrationTest.php in core/modules/dblog/tests/src/Kernel/Views/ViewsIntegrationTest.php
WorkspacePublishFormTest.php in core/modules/workspaces/tests/src/Kernel/WorkspacePublishFormTest.php

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