copy_string(aReadable.BeginReading(), aReadable.EndReading(), BeginWriting()+=oldLength);
nsReadingIterator<CharT> fromBegin, fromEnd; nsWritingIterator<CharT> toBegin; copy_string(aReadable.BeginReading(fromBegin), aReadable.EndReading(fromEnd), BeginWriting(toBegin).advance( PRInt32(oldLength) ) );
basic_nsAWritableString<CharT>::do_AppendFromReadable( const basic_nsAReadableString<CharT>& aReadable )  {    PRUint32 oldLength = this->Length();    SetLength(oldLength + aReadable.Length());    copy_string(aReadable.BeginReading(), aReadable.EndReading(), BeginWriting()+=oldLength);  }