wp-includes/class-wp-roles.php:315Sets the site to operate on. Defaults to the current site.
$site_idintoptionalnull public function for_site( $site_id = null ) { global $wpdb; if ( ! empty( $site_id ) ) { $this->site_id = absint( $site_id ); } else { $this->site_id = get_current_blog_id(); } $this->role_key = $wpdb->get_blog_prefix( $this->site_id ) . 'user_roles'; if ( ! empty( $this->roles ) && ! $this->use_db ) { return; } $this->roles = $this->get_roles_data(); $this->init_roles(); }Introduced in 4.9.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-roles.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.