Re: configuring a conditional

I thought that the person specifying the style would give more than one
of these rules, specifying what to do if the number of authors are in a
specified range, so one rule would say what to do if there were more
than 5 authors on teh
first occurrence one rule would say what to do if there are 600
authors on subsequent
occurrences etc..

The author of the style is only guided by the guidelines they must
follow.  So they're just translating the natural language specs like
"if more than six authors, then use first 3 and add et al." into a form
a processing tool can understand.

Typically, there'd just be a single rule, because typically a spec just
says "if there are more than three authors, use the first and add 'et
al.."  I'd imagine at most one might have two or three rules.  In APA
it's two for in-text citations, and one for the bibliography.  To quote
from a webpage summary for the former:

====
When a work has only two authors, use both of their names each time
their work is cited, joined by an ampersand (&) if in parentheses, or
by the word "and" if in text:

For three, four, or five authors, refer to all authors in the first
citation, then use the first authors last name followed by the
abbreviation "et al." in all subsequent citations:

For six or more authors, use the first author's last name followed by
the abbreviation et al.:

    all mentions--(Cortez et al., 1999)
====