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