    "A value getter of type `Nothing`. The expression `nothing`
     is formally assignable to any type, but produces an
     exception when evaluated.

     (This is most useful for tool-generated implementations of
     `formal` members.)"
    throws (`class AssertionError`,
            "when evaluated")
    tagged("Basic types")
    shared Nothing nothing {
        "nothing may not be evaluated"
        assert (false);
    }