code: function build_meta_information(object) {
        var res = {
          "timestamp": object.timestamp,
          "version": object.version,
          "changeset": object.changeset,
          "user": object.user,
          "uid": object.uid
        };
        for (var k in res)
          if (res[k] === undefined)
            delete res[k];
        return res;
      }
docs: helper function to extract meta information