Function ancestor 

pub fn ancestor<'a, N: Node<'a>>(n: N) -> impl Iterator<Item = N> + 'a

ancestor axis (reverse): “contains the ancestors of the context node; … the parent of the context node and the parent’s parent and so on; thus, the ancestor axis will always include the root node, unless the context node is the root node”. Results are nearest-ancestor-first (reverse document order).