[galaxy-dev] Conditional and validator: refresh_on_change without validation

Hi I'm using the <validator> tag for simple sanity checks of a tool input. But I realized that any conditional in the form will automatically call refresh_on_change which also validates all fields and prints errror messages. So questioin: is there a more galaxy-like way of checking input parameters? I am aware of the possibility to do sanity checks through custom code (http://wiki.galaxyproject.org/Admin/Tools/Custom%20Code) but the page states it should only be done if there is no other way. Regards, Tim