   always expose an attribute. If they do not have an associated attribute,
            they generate their immediate literal. If they have an associated attribute,
            the generators first test if the attribute value is equal to the immediate
            literal. They fail and do not generate anything if those are not equal.
            Otherwise they generate their immediate literal. For more information
            see for instance <a class="link" href="../karma/reference/numeric/signed_int.html"