1. https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IEnumerable.cs 2. Click the type name 3. The list is empty. In devtools you can see that GET https://source.dot.net/System.Private.CoreLib/R/3acf01620172c7f0.html returns code 500 Internal Server Error. This is not the case for, let's say, ICollection<T>.
This is not the case for, let's say, ICollection.