The onValidatePublicSubmission handler is called when a public submission form has been submitted. A common usage is checking the $_LW->_POST values for required fields and populating the $_LW->REGISTERED_MESSAGES['failure'] array to return error message(s). See below for an example module.

       'title'=>'My App',

    class LiveWhaleApplicationMyApp {

      public function onValidatePublicSubmission($data_type) { // when validating a public submission
      global $_LW;
      if ($data_type=='events') { // on submission of an event
          if (empty($_LW->_POST['event_location'])) { // require location
              $_LW->REGISTERED_MESSAGES['failure'][]='An event location must be specified.';
          if (empty($_LW->_POST['event_types'])) { // require event type
              $_LW->REGISTERED_MESSAGES['failure'][]='At least one event type must be specified.';
          if (empty($_LW->_POST['event_description'])) { // require event description
              $_LW->REGISTERED_MESSAGES['failure'][]='You must enter a description for your event.';