diff --git a/src/wp-admin/network/site-new.php b/src/wp-admin/network/site-new.php
index df98d95268..6df357a0fc 100644
--- a/src/wp-admin/network/site-new.php
+++ b/src/wp-admin/network/site-new.php
@@ -45,6 +45,7 @@ if ( isset($_REQUEST['action']) && 'add-site' == $_REQUEST['action'] ) {
 
 	// If not a subdomain install, make sure the domain isn't a reserved word
 	if ( ! is_subdomain_install() ) {
+		/** This filter is documented in wp-includes/ms-functions.php */
 		$subdirectory_reserved_names = apply_filters( 'subdirectory_reserved_names', array( 'page', 'comments', 'blog', 'files', 'feed' ) );
 		if ( in_array( $domain, $subdirectory_reserved_names ) )
 			wp_die( sprintf( __('The following words are reserved for use by WordPress functions and cannot be used as blog names: <code>%s</code>' ), implode( '</code>, <code>', $subdirectory_reserved_names ) ) );