wp-content/themes/twentytwentyone/inc/back-compat.php:81Prevents the Theme Preview from being loaded on WordPress versions prior to 5.3.
voidfunction twenty_twenty_one_preview() { if ( isset( $_GET['preview'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification wp_die( sprintf( /* translators: %s: WordPress Version. */ esc_html__( 'This theme requires WordPress 5.3 or newer. You are running version %s. Please upgrade.', 'twentytwentyone' ), esc_html( $GLOBALS['wp_version'] ) ) ); }}Introduced in Twenty Twenty-One 1.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-content/themes/twentytwentyone/inc/back-compat.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.