Function render_pager 

pub fn render_pager(
    order: &[NavLink],
    current: &str,
    root_prefix: &str,
) -> String

The pager: links to the page before and after current in the nav’s reading order, or nothing for a page that has neither.

rel="prev"/rel="next" are what a reader mode and a search engine read a sequence off. The order is crate::nav::reading_order’s — the depth-first order the sidebar lists — so a page’s “next” is the row below it.