11 files declare their use of HtmlCommand

AjaxCommandsTest.php in core/tests/Drupal/Tests/Core/Ajax/AjaxCommandsTest.php
AjaxTestController.php in core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
AjaxTestImageEffect.php in core/modules/image/tests/modules/image_module_test/src/Plugin/ImageEffect/AjaxTestImageEffect.php
ajax_forms_test.module in core/modules/system/tests/modules/ajax_forms_test/ajax_forms_test.module
Mock module for Ajax forms testing.
Callbacks.php in core/modules/system/tests/modules/ajax_forms_test/src/Callbacks.php
ContentModerationConfigureEntityTypesForm.php in core/modules/content_moderation/src/Form/ContentModerationConfigureEntityTypesForm.php
EditorImageDialog.php in core/modules/editor/src/Form/EditorImageDialog.php
EditorLinkDialog.php in core/modules/editor/src/Form/EditorLinkDialog.php
EditorMediaDialog.php in core/modules/media/src/Form/EditorMediaDialog.php
FrameworkTest.php in core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
ViewEditForm.php in core/modules/views_ui/src/ViewEditForm.php

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