public function touch($file, $time = null)
    {
        global $php_errormsg;

        if (null === $time) {
            $error = @touch($file);
        } else {
            $error = @touch($file, $time);
        }

        if (false === $error) { // FAILED.
            // Add error from php to end of log message. $php_errormsg.
            $msg = "FileSystem::touch() FAILED. Cannot touch '$file'. $php_errormsg";
            throw new Exception($msg);
        }
    }