docs; openSet options

lib/connection.js

@@ -244,7 +244,15 @@ Connection.prototype.open = function (host, database, port, options, callback) {
  *     db.openSet("mongodb://user:pwd@localhost:27020/testing,mongodb://example.com:27020,mongodb://localhost:27019");
  *
  * The database name and/or auth need only be included in one URI.
- * The `options` are passed to the internal driver connection object.
+ * The `options` is a hash which is passed to the internal driver connection object.
+ *
+ * Valid `options`
+ *
+ *     db      - passed to the connection db instance
+ *     server  - passed to the connection server instance(s)
+ *     replset - passed to the connection ReplSetServer instance
+ *     user    - username for authentication
+ *     pass    - password for authentication
  *
  * @param {String} uris comma-separated mongodb:// `URI`s
  * @param {String} [database] database name if not included in `uris`