12 files declare their use of AttachedAssets

AjaxCommandsTest.php in core/tests/Drupal/Tests/Core/Ajax/AjaxCommandsTest.php
AjaxResponseAttachmentsProcessor.php in core/lib/Drupal/Core/Ajax/AjaxResponseAttachmentsProcessor.php
AnnounceCommand.php in core/lib/Drupal/Core/Ajax/AnnounceCommand.php
AssetResolverTest.php in core/tests/Drupal/Tests/Core/Asset/AssetResolverTest.php
Contains \Drupal\Tests\Core\Asset\AssetResolverTest.
AttachedAssetsTest.php in core/tests/Drupal/KernelTests/Core/Asset/AttachedAssetsTest.php
BigPipe.php in core/modules/big_pipe/src/Render/BigPipe.php
CommandWithAttachedAssetsTrait.php in core/lib/Drupal/Core/Ajax/CommandWithAttachedAssetsTrait.php
FrameworkTest.php in core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
HtmlResponseAttachmentsProcessor.php in core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php
LocaleLibraryAlterTest.php in core/modules/locale/tests/src/Kernel/LocaleLibraryAlterTest.php
MessageCommand.php in core/lib/Drupal/Core/Ajax/MessageCommand.php
simpletest.module in core/modules/simpletest/simpletest.module
Provides testing functionality.

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