do_action( 'switch_theme', string $new_name, WP_Theme $new_theme, WP_Theme $old_theme )

872	 * @since 4.5.0 Introduced the `$old_theme` parameter.873	 *874	 * @param string   $new_name  Name of the new theme.875	 * @param WP_Theme $new_theme WP_Theme instance of the new theme.876	 * @param WP_Theme $old_theme WP_Theme instance of the old theme.877	 */878	do_action( 'switch_theme', $new_name, $new_theme, $old_theme );879}880 881/**882 * Checks that the active theme has the required files.883 *884 * Standalone themes need to have a `templates/index.html` or `index.php` template file.