code: public final int _nextsib2(int identity)
    {
      //return m_nextsib.elementAt(identity);
  
      if (identity < m_blocksize)
        return m_nextsib_map0[identity];
      else
        return m_nextsib_map[identity>>>m_SHIFT][identity&m_MASK];
    }
docs: The optimized version of DTMDefaultBase._nextsib().
  
  @param identity A node identity, which <em>must not</em> be equal to
  <code>DTM.NULL</code>