The SRFI document says:
========================
The vectors of upper and lower bounds of an interval can have zero
elements, in which case the zero-dimensional interval itself has no
elements, but zero-dimensional arrays with this domain have getters and
setters that take zero indices as arguments, and which return or set a
single element, much like a Scheme box.
========================
It also says, in an offhand way:
========================
(Multi-indices correspond to Scheme values.)
========================
The second statement is more profound than I realized, because in SRFI
231 multi-indices are precisely what's returned by

(values), or
(values i_0), or
(values i_0 i_1), etc.

So (values), by itself, is a valid multi-index.

The first statement is therefore incorrect, a zero-dimensional interval
has a single element, namely (values).

This is a bit mind-bending, and I made quite a number of edits in the
SRFI followup I've been working on to deal with it:

https://github.com/gambiteer/srfi-231/commit/eee76aa50b4d63970a8bab2e5f7b5fdc4d20aa0d

Perhaps a simple, short fix is appropriate for the SRFI document.

Brad