operator+=( difference_type(n) );
advance( difference_type(n) );
      write( const value_type* s, PRUint32 n )        {          NS_ASSERTION(size_forward() > 0, "You can't |write| into an |nsWritingIterator| with no space!");          n = NS_MIN(n, PRUint32(size_forward()));          nsCharTraits<value_type>::move(mPosition, s, n);          operator+=( difference_type(n) );          return n;        }