function parseTime(str) {
        if (!str) {
            return 0;
        }

        var strings = str.split(":");
        var l = strings.length, i = l;
        var ms = 0, parsed;

        if (l > 3 || !/^(\d\d:){0,2}\d\d?$/.test(str)) {
            throw new Error("tick only understands numbers and 'h:m:s'");
        }

        while (i--) {
            parsed = parseInt(strings[i], 10);

            if (parsed >= 60) {
                throw new Error("Invalid time " + str);
            }

            ms += parsed * Math.pow(60, (l - i - 1));
        }

        return ms * 1000;
    }
Parse strings like "01:10:00" (meaning 1 hour, 10 minutes, 0 seconds) into
number of milliseconds. This is used to support human-readable strings passed
to clock.tick()