Error "Elements defined in a namespace cannot be explicitly declared as private, protected, or protected internal"

Question

I tried to make a class as private and got this Error "Elements defined in a namespace cannot be explicitly declared as private, protected, or protected internal"

I got its meaning but I want to ask why this is not allowed? Are all access modifires not applicable on Class? Why I can't make a class private, protected or protected internal?

Answer 1

Because private means that the member is only visible in the containing class. Since a top-level class has no class containing it it cannot be private (or protected). (Internal or public are valid modifiers though).

What would you want private to mean on a top-level class?

Of course all modifiers apply to nested classes, i.e. a class defined within another class.

Answer 2

You can use only public or internal in the Namespace level

Answer 3

As Abatonime said, you can only use public or internal in the Namespace level.
private, protected, or protected internal can only be used in the Class level.

This works

namespace X
{
    class A
    {
        // class code here

        private class B // this class is an inner class
        {
            // class code here
        }
    }
}

This won't

namespace X
{
    class A
    {
        // class code here
    }

    private class B // this is a class inside a namespace
    {
        // class code here
    }
}