fragmenting_writer.go
func (w *fragmentingWriter) ArgWriter(last bool) (ArgWriter, error) {
	if err := w.BeginArgument(last); err != nil {
		return nil, err
	}
	return w, nil
}
func (w *fragmentingWriter) ArgWriter(last bool) (ArgWriter, error) {
	if err := w.BeginArgument(last); err != nil {
		return nil, err
	}
	return w, nil
}
// ArgWriter returns an ArgWriter to write an argument. The ArgWriter will handle
// fragmentation as needed. Once the argument is written, the ArgWriter must be closed.