WordPress at a glance
filter is not described

network_site_url filter-hook . WP 3.0.0

Filters the network site URL.

Usage

add_filter( 'network_site_url', 'filter_function_name_7285', 10, 3 );
function filter_function_name_7285( $url, $path, $scheme ){
	// filter...

	return $url;
}
$url(string)
The complete network site URL including scheme and path.
$path(string)
Path relative to the network site URL. Blank string if no path is specified.
$scheme(string/null)
Scheme to give the URL context. Accepts 'http', 'https', 'relative' or null.

Where the hook is called

network_site_url()
wp-includes/link-template.php 3229
return apply_filters( 'network_site_url', $url, $path, $scheme );

Where the hook is used (in WP core)

Does not used.