Side navigation
The section tree, rendered from the content directory and opened to the page you are on.
Where it comes from
Nothing declares this menu. It is the content directory: every page under the
top-level section, ordered by weight, nested exactly as the directories are.
Add a folder with an _index.md and it appears.
The nav is rooted at the top of the tree rather than at the page’s parent. Rooted at the parent, this page would list only its two siblings, and the rest of the documentation would disappear the moment you opened a subsection.
What it renders
| Page position | What you see |
|---|---|
| Sibling | plain link |
| Open section | blue rule, bold |
| Current page | blue text, aria-current |
Only the open branch renders its children. Emitting every descendant of every section would put the whole site in the DOM of every page — a payload cost, and a screen reader would have to walk all of it.
Depth
This page sits three levels down — Documentation, Components, Navigation — and the branch above it is open on the left. The partial recurses without a depth limit; USWDS styles the indentation to three levels of sublist.
Section index pages keep the nav too
Clicking a subsection in the sidenav lands on its index page. That page is a list, not an article, but it renders the same tree — otherwise navigation would vanish exactly where a reader is most likely to be looking for it.