Referential Integrity / Hacking RI Tutorial

I've written the start of a tutorial on how to use the RI features of
Pgsql, and how to alter the system catalogs to change actions,
deferrability, etc. Much of the information is already in the docs, but
spread around different SQL reference sections, etc., so I thought it
would be useful in one place.

It's not in Docbook; I want to see first what structural changes people
can recommend, etc., before it gets marked up.

It's a bit rough, so I'd hold off on grammar/spelling/etc., but I would be
interested if people have (a) tips not in it, (b) factual errors, or
(c) ideas about where it might fit into the docs.

I do read this group, but I always like a cc: to make sure I don't miss
anything: jburton(at)scw(dot)org(dot)

Thanks!