mParent->ChildAt(childIndex, *getter_AddRefs(child));
mParent->ChildAt(childIndex, getter_AddRefs(child));
nsTableCellCollection::GetLength(PRUint32* aLength){  if (!aLength) {    return NS_ERROR_NULL_POINTER;  }  *aLength = 0;  nsresult result = NS_OK;  if (mParent) {    nsCOMPtr<nsIContent> child;    PRUint32 childIndex = 0;    mParent->ChildAt(childIndex, *getter_AddRefs(child));    while (child) {      nsCOMPtr<nsIAtom> childTag;      child->GetTag(*getter_AddRefs(childTag));      if ((nsHTMLAtoms::td == childTag.get()) ||          (nsHTMLAtoms::th == childTag.get())) {        (*aLength)++;      }      childIndex++;      mParent->ChildAt(childIndex, *getter_AddRefs(child));    }  }  return result;}