This type is enumerable because it inherits from IEnumerable`1.

The extension methods erload:System.Linq.Enumerable.ThenBy and erload:System.Linq.Enumerable.ThenByDescending operate on objects of type System.Linq.IOrderedEnumerable`1. An object of type System.Linq.IOrderedEnumerable`1 can be obtained by calling one of the primary sort methods, erload:System.Linq.Enumerable.OrderBy or erload:System.Linq.Enumerable.OrderByDescending, which return an System.Linq.IOrderedEnumerable`1. erload:System.Linq.Enumerable.ThenBy and erload:System.Linq.Enumerable.ThenByDescending, the subordinate sort methods, in turn also return an object of type System.Linq.IOrderedEnumerable`1. This design allows for any number of consecutive calls to erload:System.Linq.Enumerable.ThenBy or erload:System.Linq.Enumerable.ThenByDescending, where each call performs a subordinate ordering on the sorted data returned from the previous call.

Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Assembly Versions: 3.5.0.0, 4.0.0.0