nsresult nsContentIterator::Prev()
nsresult nsContentSubtreeIterator::Prev()
nsresult nsContentIterator::Prev(){  if (mIsDone)     return NS_OK;  if (!mCurNode)     return NS_OK;  if (mCurNode == mFirst)   {    mIsDone = PR_TRUE;    return NS_OK;  }    return PrevNode(address_of(mCurNode), &mIndexes);}