nsresult nsContentIterator::Next()
nsresult nsContentSubtreeIterator::Next()
nsresult nsContentIterator::Next(){  if (mIsDone)     return NS_ERROR_FAILURE;  if (!mCurNode)     return NS_OK;  if (mCurNode == mLast)   {    mIsDone = PR_TRUE;    return NS_ERROR_FAILURE;  }    return NextNode(&mCurNode);}