system.theme.yml

BlockTheme::create in core/modules/block/src/Plugin/migrate/process/BlockTheme.php

Creates an instance of the plugin.

CKEditor5CacheTag::onSave in core/modules/ckeditor5/src/EventSubscriber/CKEditor5CacheTag.php

Invalidates cache tags when particular system config objects are saved.

ConfigCacheTag::onSave in core/modules/system/src/EventSubscriber/ConfigCacheTag.php

Invalidate cache tags when particular system config objects are saved.

ConfigImporter::processExtension in core/lib/Drupal/Core/Config/ConfigImporter.php

Processes an extension change.

FunctionalTestSetupTrait::installDefaultThemeFromClassProperty in core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php

Installs the default theme defined by `static::$defaultTheme` when needed.

... See full list