mDataSources.RemoveElement(aDataSource);
CompositeDataSourceImpl::RemoveDataSource(nsIRDFDataSource* aDataSource){    NS_ASSERTION(aDataSource != nsnull, "null ptr");    if (! aDataSource)        return NS_ERROR_NULL_POINTER;    if (mDataSources.IndexOf(aDataSource) >= 0) {        mDataSources.RemoveElement(aDataSource);        aDataSource->RemoveObserver(this);        NS_RELEASE(aDataSource);    }    return NS_OK;}