NS_IMETHOD ContentChanged(nsIDocument *aDocument, nsIContent* aContent, nsISupports* aSubContent) { return NS_OK; }
NS_IMPL_NSIDOCUMENTOBSERVER_CONTENT(HTMLContentSink)
  NS_IMETHOD ContentChanged(nsIDocument *aDocument, nsIContent* aContent,                            nsISupports* aSubContent)  {    return NS_OK;  }