Class it_url:

/**
 * Construct a local directory name to cache an URL. Named args:
 * @param $p['cachedir']    directory to store cache files in, defaults to $ULTRAHOME/var/urlcache
 * @param $p['id']          If you need more than one type of cache (e.g. different maxage) you can specify an id
 */
static function get_cache_dir($p)
{
    $p += array('cachedir' => $GLOBALS['ULTRAHOME'] . "/var/urlcache", 'id' => "default");
    return rtrim($p['cachedir'] . "/" . $p['id'], "/");
}