this.listeners = new HashSet();
  protected DomNode(short nodeType, DomDocument owner)  {    this.nodeType = nodeType;    if (owner == null)      {        // DOM calls never go down this path        if (nodeType != DOCUMENT_NODE && nodeType != DOCUMENT_TYPE_NODE)          {            throw new IllegalArgumentException ("no owner!");          }      }    this.owner = owner;  }