'is(T==return)' How does is expression with return keyword as TypeSpecialization

[Timoses via Digitalmars-d-learn]

    int fun(T)(T i)
    {
        static assert(is(typeof(return) == T)); //true
        pragma(msg, is(T == return)); // false
        static if (is(T ReturnType == return))
            pragma(msg, ReturnType); // does not enter
        return i;
    }
    unittest
    {
        fun(3);
    }

What's the purpose of 'is(T == return)' if not the above?