public function processValue()
    {
        $form = $this->getForm();

        if ($form->getHiddenField($this->id . '_submitted') === null) {
            return false;
        }

        $data = &$form->getFormData();

        if (isset($data[$this->id])) {
            // get selected page id, strip off this id prefix
            $this->selected_page = mb_substr(
                $data[$this->id],
                mb_strlen($this->id) + 1
            );
        } else {
            $this->selected_page = null;
        }

        return true;
    }