TableOfContents
In-page anchor list the server rendered; the module marks the active entry.
Live
What it is
A labelled nav of fragment links. The server renders every entry, so a reader without script still gets the list.
How it works
The headless-toc module watches the target region and marks the entry whose heading is in view — aria-current and a class, never a style.
The active entry
The observer is headless-rail's, shared with AnchoredRail: one implementation, not two scroll-spies.