PRInt32 count = Count() - 1; NS_ENSURE_TRUE(count >= 0, nsnull);  return ElementAt(count);
NS_ASSERTION(!isEmpty(), "peeking at empty stack"); return ElementAt(Count() - 1);
    void* peek()    {        PRInt32 count = Count() - 1;        NS_ENSURE_TRUE(count >= 0, nsnull);        return ElementAt(count);    }