>> I'd provide all five ci procedures; people will expect them.
>
> I'll add them and make a new draft.

I'm implementing these using `open-input-string` which ought to be
faster than `string-ref` on big strings. Does the port it returns need
to be closed - does it matter? I'd imagine adding `call-with-port` makes
things slower, and the port is going to be GC'ed soon even without it.