Validation

function onResponsePre(ResponseEvent $event) {
            // Execute this code before any PenPusher response is sent.
            // By setting the cancelAction property you will cancel the standard
            // message and it is assumed that you have sent your own.
            g_Log(__METHOD__. " ".$event->response->type. " ".$event->response->message);

            //Set the page of the document to $page
            $page = $event->document->pages[0];

            //if any of the fields are empty promt the user to fill in that field
              if (strlen($page->fields["First_Name"]->value) === 0 ||
                 strlen($page->fields["Surname"]->value) === 0||
                 strlen($page->fields["Title"]->value) === 0||
                 strlen($page->fields["Email"]->value) === 0 ||
                       ($page->fields["Box1"]->value != 'true' &&
                        $page->fields["Box2"]->value != 'true' &&
                        $page->fields["Box3"]->value != 'true' &&
                        $page->fields["Box4"]->value != 'true' &&
                        $page->fields["Box5"]->value != 'true' &&
                        $page->fields["Box6"]->value != 'true')
                      )
                 {
                        //Find which field is missing.
                        $error = "Please Enter:";
                        if(strlen($page->fields["Title"]->value) === 0){$error .= "\n Title";   }
                        if(strlen($page->fields["First_Name"]->value) === 0){$error .= "\n First Name"; }
                        if(strlen($page->fields["Surname"]->value) === 0){$error .= "\n Surname";   }
                        if(strlen($page->fields["Email"]->value) === 0){$error .= "\n Email";   }
                        if($page->fields["Email"]->value != 'true'){$error .= "\n   Tick at least one product to find out more information.";
                        //Set the response message
                        $event->response->message = $error ;
                        //Abort the penpusher and set yellow icon
                        $event->response->type = PenPusherResponse::ABORT;
                 }
          }//end onResponsePre