good catch. support both separately, but we should we prevent mixing both in the same URI at the same time? the python driver raises an error in that case, the C# driver doesn't. I haven't looked at Java yet.

https://github.com/mongodb/mongo-csharp-driver/blob/master/MongoDB.Driver/MongoUrlBuilder.cs#L803
https://github.com/mongodb/mongo-python-driver/blob/master/pymongo/uri_parser.py#L171-L180