Hans Aberg writes:

 > I tend to think that there in a text mode for natural language alone, there
 > should be no numbers allowed, only letters and punctuation marks. Thus your
 > AW quote should be

i don't quite agree. there are certainly schools that would like to bann
numbers in a context like this but even if you spell out all such number as
text you still have the problem that you have to allow textual number, or are
you really proposing that a reference to a page or a figure or heading has to
be as "see figure seven.three"?

and depending on the design such number might get  quite a different treatment
to those being part of a math formula (eg they might be in old style or they
might be in the text font family or ...)

so there are "textual digits" and there are "mathematical digits".