private function _validateColumn(array $data)
    {
        if (!isset($data['label'])) {
            return 'Label key is required.';
        }
        if (!isset($data['index'])) {
            return 'Index key is required.';
        }

        if (isset($data['renderer']) && (!$data['renderer'] instanceof \Closure && !is_string($data['renderer']))) {
            return 'Renderer must be a string or instance of Closure object.';
        }

        if (isset($data['filter']) && !$data['filter'] instanceof \Closure) {
            return 'Filter function must be instance of Closure object.';
        }

        return true;
    }