Why doesn't the C#/VB.NET compiler allow classes to be derived from System.MulticastDelegate?

What was the rationale behind prohibiting users from inheriting from开发者_开发知识库 System.MulticastDelegate?

MulticastDelegate is only meant for the compilers themselves to create delegate types, which all derive from MulticastDelegate. It is not meant to be subclassed by users. This is similar to System.ValueType which is only meant for implementing struct types.