wp-includes/ms-functions.php:2400Determines whether users can self-register, based on Network settings.
boolfunction users_can_register_signup_filter() { $registration = get_site_option( 'registration' ); return ( 'all' === $registration || 'user' === $registration );}Introduced in MU (3.0.0). Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/ms-functions.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.