QuickForm_Controller - Custom Action

Hi i need to access the contents of the container right _after_ the user clicked the NEXT-button in a multipagewizard form and _before_ the controller takes care of analyzing the container-data for the current page and takes proper actions. does anyone know where this point in quickform controller package is? (hey alexey, how r u doing? ;) i tried writing a custom next-action, but this does not seem to be the right point. thanks in advance, /matthias