Why declare static classes as sealed and abstract in C#?

c#

Solution

I think the pertinent bit from that article is:

"Do declare static classes as sealed and abstract, and add a private instance constructor, if your programming language does not have built-in support for static classes."

Remember, the .NET framework supports a lot of different languages.

Problem

This MSDN article states that static classes should be declared as sealed and abstract. I was under the impression that static classes were already sealed. Why would you also need to declare a static class as sealed?

Original source

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