public function getValidationError($field)
    {
        // break apart path
        $crumbs = explode('.', $field);

        // resolve path recursively
        $cur = &$this->_validationErrors;
        while ($crumb = array_shift($crumbs)) {
            if (array_key_exists($crumb, $cur)) {
                $cur = &$cur[$crumb];
            } else {
                return null;
            }
        }

        // return current value
        return $cur;
    }