public function exportValue(&$submitted, $assoc = false) {

        $value = '';
        $filetypeselement = null;

        foreach ($this->_elements as $key => $element) {
            if ($element->_attributes['name'] === 'filetypes') {
                $filetypeselement = $this->_elements[$key];
            }
        }

        if ($filetypeselement) {
            $formval = $filetypeselement->exportValue($submitted[$this->getName()], false);
            if ($formval) {
                $value = $this->util->normalize_file_types($formval);
                if ($value === ['*'] && !$this->allowall) {
                    $value = [];
                }
                $value = implode(',', $value);
            }
        }

        return $this->_prepareValue($value, $assoc);
    }