How do I create a CLR UDF with external name specifying namespace, class, and subclass?

Question

I am creating a CLR UDF using external name and second level nested class names seem not to be permitted. Is this the case? When using the following syntax and including a first level class name and associated method, I am able to bind a UDF to the method, but not if I included additional subclass levels.

    CREATE FUNCTION [dbo].[udf_test](@variable [nvarchar](MAX))
    RETURNS [nvarchar](MAX) WITH EXECUTE AS CALLER
    AS 
    EXTERNAL NAME [assembly].[ns.first.second].[method]
    GO

Thanks