(Yaf >=1.0.0)
An action can be defined in a separate file in Yaf (see Yaf_Controller_Abstract). That is, an action method can also be a Yaf_Action_Abstract class.
Since there should be a entry point which can be called by Yaf, you must implement the abstract method Yaf_Action_Abstract::execute() in your custom action class.
The controller instance that owns this action, retrievable with Yaf_Action_Abstract::getController().