https://mongodb.github.io/mongo-csharp-driver/2.13/apidocs/html/Overload_MongoDB_Driver_IndexKeysDefinitionExtensions_Descending.htm
IndexKeysDefinitionExtensions.Descending Method
descendingmethod
https://mongodb.github.io/mongo-csharp-driver/2.3/apidocs/html/Overload_MongoDB_Driver_IndexKeysDefinitionExtensions_Text.htm
IndexKeysDefinitionExtensions.Text Method
textmethod
https://mongodb.github.io/mongo-csharp-driver/3.0.0/api/MongoDB.Driver/MongoDB.Driver.IndexKeysDefinitionExtensions.html
Class IndexKeysDefinitionExtensions | MongoDB CSharp Driver API Reference
classmongodbcsharpdriverapi