WordPress at a glance
filter is not described

domain_exists filter-hook . WP 3.5.0

Filters whether a site name is taken.

The name is the site's subdomain or the site's subdirectory path depending on the network settings.

Usage

add_filter( 'domain_exists', 'filter_function_name_2329', 10, 4 );
function filter_function_name_2329( $result, $domain, $path, $network_id ){
	// filter...

	return $result;
}
$result(int/null)
The site ID if the site name exists, null otherwise.
$domain(string)
Domain to be checked.
$path(string)
Path to be checked.
$network_id(int)
Network ID. Relevant only on multi-network installations.

Where the hook is called

domain_exists()
wp-includes/ms-functions.php 1383
return apply_filters( 'domain_exists', $result, $domain, $path, $network_id );

Where the hook is used (in WP core)

Does not used.