Define indexing at the BsonValue level so that indexing is available automatically without having to downcast the BsonValue to a BsonDocument or BsonArray. If indexing is invoked on a BsonValue that is not a document or array an InvalidOperationException will be thrown.

This allows code to be written much more concisely. For example:

var streetAddress = document.AsBsonDocument["Addresses"].AsBsonArray[0].AsBsonDocument[0].AsString;

can now be written simply as:

var streetAddress = document["Addresses"][0][0].AsString;

NOTE: this new feature is not really compatible with the proposal in CSHARP-558, but might be preferable to CSHARP-558.