System has various action and filter hooks throughout its files. You may browse through them and search for "hook::action" or "hook::filter" to find available hook placeholders and their parameters. Below is a list of system hooks.
System starts, no libraries or models are loaded yet.
All default libraries and models are loaded.
Controller is loaded but not executed yet.
Controller's constructor is executed but not the action. [name] represents the name of the controller.
Controller's action is executed. [name] represents the name of the controller and [action] its action (function name).
Controller action is executed but specified "view" file is not loaded yet.
View file is loaded but nothing is displayed yet.
Output is displayed.