This looks like it have all of the information that I need. For some reason search engines bring up many other pages but not that one.
For these situations I recommend bookmarking and navigating to the Table of Contents [1] for the documentation and looking for relevant chapter titles - in this case the "V. 38 - Triggers" one is right there on the main page.
On a related note, maybe the pl/pgsql link from the Triggers chapter should link directly to the Triggers section under pl/pgsql instead of the top of the chapter...