I've just found (via google...) useful (for me) comments:
http://www.postgresql.org/docs/8.0/interactive/sql-createaggregate.html
-- I mean users comments under primary contents of the page.
These comments were written for 8.0, but are useful for the current
versions too. What we have is the situation that reading docs for 8.2
people don't see these comments -- so this potentially useful
information is lost. So, in this implementation the idea of comments
for docs becomes weak in general.
In some other OSS projects comments for docs are used intensively and
hold a lot of useful information for many people. The good example
here is PHP docs -- sometimes comments are much more useful and much
more important then the main contents itself!
I understand that comments migration and maintenance might be a hard
task, because some comments may be really out-dated... Maybe simple
notice like "this comment was created for pg 8.0 docs" would help.
--
Best regards,
Nikolay