Comment by restalis

Your range checking requirement is just one of many things that may or may not be necessary to someone using this. Taking them all into account (besides the fact that may be unfeasible, if there happen to be some conflicting requirements) would render the solution to be unnecessarily complex. It's better to focus on the minimal set of viable requirements and thus have a base design as simple as possible. For additional requirements, just go and complicate your design (and be the only one having to pay the costs that come out of that complication), hopefully only when and only for as long it makes sense to do so. For the need you mention, some kind of container wrapper may do, with the amount of number's words specified in it. A good thing is that you'd be able to limit the use of such container-wrapped numbers only to some situations (like the exchange of data to and from unsanitized areas).