code: public void insertNode(Node n, int pos)
    {
  
      if (!m_mutable)
        throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NODESET_NOT_MUTABLE, null)); //"This NodeSet is not mutable!");
  
      insertElementAt(n, pos);
    }
docs: Insert a node at a given position.
  
  @param n Node to be added
  @param pos Offset at which the node is to be inserted,
  with 0 being the first position.
  @throws RuntimeException thrown if this NodeSet is not of
  a mutable type.