code: public void addNodes(NodeSet ns)
    {
  
      if (!m_mutable)
        throw new RuntimeException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_NODESET_NOT_MUTABLE, null)); //"This NodeSet is not mutable!");
  
      addNodes((NodeIterator) ns);
    }
docs: <p>Copy NodeList members into this nodelist, adding in
  document order.  Only genuine node references will be copied;
  nulls appearing in the source NodeSet will
  not be added to this one. </p>
  
  <p> In case you're wondering why this function is needed: NodeSet
  implements both NodeIterator and NodeList. If this method isn't
  provided, Java can't decide which of those to use when addNodes()
  is invoked. Providing the more-explicit match avoids that
  ambiguity.)</p>
  
  @param ns NodeSet whose members should be merged into this NodeSet.
  @throws RuntimeException thrown if this NodeSet is not of
  a mutable type.