Chapter 3. Hooks, Actions, and Triggers, Page 41
Not strictly an error, but definitely a gotcha for the unwary user. The book says: If you've done everything correctly, your action should be available in the user interface [...] Some users of Drupal 6.6 (and possibly other versions) may find this misleading and waste time looking for errors in their code, which may not be there or, at any rate, not have anything to do with the observed effect of the actions not becoming available.
State that you may have to click on admin/settings/actions in order for your changes to be reflected on the admin/build/trigger page.
I've left the path of strict and verbatim obedience to the book's prescription, and defined the actions in a module that had already been installed. The actions didn't show up in the user interface. In Drupal 6.6, which is what I'm using, you have to click on admin/settings/actions in order for the actions to be registered in the actions table, whence they are retrieved to be displayed in the dropdown menus on admin/build/trigger.