code: public int addNodeInDocOrder(int node, XPathContext support)
    {
  
      if (!m_mutable)
        throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NODESETDTM_NOT_MUTABLE, null)); //"This NodeSetDTM is not mutable!");
  
      return addNodeInDocOrder(node, true, support);
    }
docs: Add the node into a vector of nodes where it should occur in
  document order.
  @param node The node to be added.
  @param support The XPath runtime context.
  
  @return The index where it was inserted.
  @throws RuntimeException thrown if this NodeSetDTM is not of
  a mutable type.