Coding standards? Recommendations?

I've noticed a variety of coding styles in the PostgreSQL source code. In
particular, I see a mix of naming conventions. Some variables use camelCase
(or CamelCase), others use under_score_style.

I'm just wondering if there's a preferred naming convention. Is there an
official convention? An unofficial recommendation? Or even a majority
preference?

I'm not necessarily arguing for an official standard, but I'd be happy to
follow a standard/recommendation if there is one. I find it just as easy to
write conforming code as non-conforming code.

(sorry if this has been covered before - if you can point me to a document
that covers the information I'm looking for, that would be very helpful).

-- Korry