return nsPromiseConcatenation<CharT>(*this, rhs, mFragmentIdentifierMask<<1);
return nsPromiseConcatenation<CharT>(lhs, rhs);
nsPromiseConcatenation<CharT>::operator+( const basic_nsAReadableString<CharT>& rhs ) const  {    return nsPromiseConcatenation<CharT>(*this, rhs, mFragmentIdentifierMask<<1);  }