wp-includes/ms-load.php:18Whether a subdomain configuration is enabled.
boolfunction is_subdomain_install() { if ( defined( 'SUBDOMAIN_INSTALL' ) ) { return SUBDOMAIN_INSTALL; } return ( defined( 'VHOST' ) && 'yes' === VHOST );}Introduced in 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-load.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.