@Rick-Anderson  Should it be mentioned here that `IServiceCollection `is a collection of ServiceDescriptor and an example of adding it like that explicitly (as below)? And state the extension methods makes it easier to add registrations.  ```  var item = new ServiceDescriptor(typeof(IMyDependency), context = >new MyDependency(),                                                           ServiceLifetime.Transient);    services.Add(item);  ```