Creating a New Event

hook_rules_event_info is documented at http://drupal.org/node/298549 as one of the hooks required to build a custom event.
However, a for this hooks comes up empty (e.g., it doesn't exist). Very little doubt that it indeed does exist, but where? And why is it so hard to find?

And if it is in an obscure place, shouldn't the documentation (http://drupal.org/node/298549) mention that location?

Thanks in advance for clues!