{"ast_node_type":"function","tokens":[{"end":97,"kind":"keyword","start":0,"text":"pub(crate)"}]}
    pub(crate) fn universal_regions_outlived_by(&self, r: N) -> impl Iterator<Item = RegionVid> {
    /// Returns just the universal regions that are contained in a given region's value.
        self.free_regions.row(r).into_iter().flat_map(|set| set.iter())