cssSheet->SetDefaultNameSpaceID(nsMathMLAtoms::nameSpaceID);
cssSheet->SetDefaultNameSpaceID(kNameSpaceID_MathML);
GetMathMLAttributeStyleSheet(nsIPresContext* aPresContext,                             nsIStyleSheet** aSheet){  static const char kTitle[] = "Internal MathML/CSS Attribute Style Sheet";  *aSheet = nsnull;  // first, look if the attribute stylesheet is already there  nsCOMPtr<nsIPresShell> presShell;  aPresContext->GetShell(getter_AddRefs(presShell));  nsCOMPtr<nsIStyleSet> styleSet;  presShell->GetStyleSet(getter_AddRefs(styleSet));  if (!styleSet)    return;  nsAutoString title;  for (PRInt32 i = styleSet->GetNumberOfAgentStyleSheets() - 1; i >= 0; --i) {    nsCOMPtr<nsIStyleSheet> sheet = getter_AddRefs(styleSet->GetAgentStyleSheetAt(i));    nsCOMPtr<nsICSSStyleSheet> cssSheet(do_QueryInterface(sheet));    if (cssSheet) {      cssSheet->GetTitle(title);      if (title.Equals(NS_ConvertASCIItoUCS2(kTitle))) {        *aSheet = sheet;        NS_IF_ADDREF(*aSheet);        return;      }    }  }  // then, create a new one if it isn't yet there  nsCOMPtr<nsIURI> uri;  NS_NewURI(getter_AddRefs(uri), "about:internal-mathml-attribute-stylesheet");  if (!uri)    return;  nsCOMPtr<nsICSSStyleSheet> cssSheet(do_CreateInstance(kCSSStyleSheetCID));  if (!cssSheet)    return;  cssSheet->Init(uri);  cssSheet->SetTitle(NS_ConvertASCIItoUCS2(kTitle));  cssSheet->SetDefaultNameSpaceID(nsMathMLAtoms::nameSpaceID);  nsCOMPtr<nsIStyleSheet> sheet(do_QueryInterface(cssSheet));  // insert the stylesheet into the styleset without notifying observers  styleSet->AppendAgentStyleSheet(sheet);  *aSheet = sheet;  NS_ADDREF(*aSheet);}