code: public final void popPair()
    {
  
      m_firstFree -= 2;
      m_map[m_firstFree] = DTM.NULL;
      m_map[m_firstFree + 1] = DTM.NULL;
    }
docs: Pop a pair of nodes from the tail of the stack.
  Special purpose method for TransformerImpl, pushElemTemplateElement.
  Performance critical.