According to http://yaml-online-parser.appspot.com/?url=https%3A%2F%2Fraw.github.com%2Fyast%2Fyast-ntp-client%2F4190c29173d7d180a6be5aa0d5aa22de9b8fa90c%2Fsrc%2Fdata%2Fntp_servers.yml -- there is no change if I take `!` out and I also haven't found it in specification.