wp-content/themes/twentynineteen/inc/back-compat.php:21Prevents switching to Twenty Nineteen on old versions of WordPress.
function twentynineteen_switch_theme() { switch_theme( WP_DEFAULT_THEME ); unset( $_GET['activated'] ); add_action( 'admin_notices', 'twentynineteen_upgrade_notice' );}Introduced in Twenty Nineteen 1.0.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-content/themes/twentynineteen/inc/back-compat.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.