docs: function UpdateSet(options, callback) {
      var set_opts = {
          additions: options.additions,
          removals: options.removals
      };
      delete options.additions;
      delete options.removals;
  
      UpdateSetBase.call(this, options, callback);
  
      var self = this;
      Joi.validate(set_opts, schema, function(err, opts) {
          if (err) {
              throw err;
          }
          self.additions = opts.additions;
          self.removals = opts.removals;
      });
  }