WordPress at a glance
filter is not described

site_by_path_segments_count filter-hook . WP 3.9.0

Filters the number of path segments to consider when searching for a site.

Usage

add_filter( 'site_by_path_segments_count', 'filter_function_name_4499', 10, 3 );
function filter_function_name_4499( $segments, $domain, $path ){
	// filter...

	return $segments;
}
$segments(int/null)
The number of path segments to consider. WordPress by default looks at one path segment following the network path. The function default of null only makes sense when you know the requested path should match a site.
$domain(string)
The requested domain.
$path(string)
The requested path, in full.

Where the hook is called

get_site_by_path()
site_by_path_segments_count
wp-includes/ms-load.php 170
$segments = apply_filters( 'site_by_path_segments_count', $segments, $domain, $path );

Where the hook is used (in WP core)

Does not used.