// If multisite (and if not the main site in a post-MU network)
if ( is_multisite() && ! ( is_main_network() && is_main_site() && defined( 'MULTISITE' ) ) ) {
if ( ! get_site_option( 'ms_files_rewriting' ) ) {
/*
* If ms-files rewriting is disabled (networks created post-3.5), it is fairly
* straightforward: Append sites/%d if we're not on the main site (for post-MU
* networks). (The extra directory prevents a four-digit ID from conflicting with
* a year-based directory for the main site. But if a MU-era network has disabled
* ms-files rewriting manually, they don't need the extra directory, as they never
* had wp-content/uploads for the main site.)
*/
if ( defined( 'MULTISITE' ) )
$ms_dir = '/sites/' . get_current_blog_id();
else
$ms_dir = '/' . get_current_blog_id();
$dir .= $ms_dir;
$url .= $ms_dir;
...
}}