To allow using Actions as Contexts, the ActionValidationController extends the Application Model. The ValidationContexts property is added to the ActionDesign | Actions | <Action> node. Additionally, the Controller adds a handler to the ActionBase.Executing event of each Action. In the event handler, the ActionValidationController invokes the Validator.RuleSet's RuleSet.ValidateAll method.
Generally, there is no need to inherit from the ActionValidationController, unless you want to disable the capability for using Actions as Validation Contexts. In this instance, inherit from the ActionValidationController, and override the protected OnFrameAssigned method, so that its body is empty.