hc-toc is a pure-CSS skin over a labeled <nav> wrapping a list of in-page anchor links — the familiar “On this page” jump list for long reference pages. It works with no JavaScript. Add data-hc-spy and the installSpy behavior marks the link of the section currently in view as the reader scrolls.

Basic example

The active link below is marked statically with aria-current="location" to show the styling; with data-hc-spy the behavior sets it for you.

<nav class="hc-toc" aria-label="On this page">
  <ul class="hc-toc__list">
    <li class="hc-toc__item"><a class="hc-toc__link" href="#sec-inputs">Inputs</a></li>
    <li class="hc-toc__item"><a class="hc-toc__link" href="#sec-sql">SQL</a></li>
    <li class="hc-toc__item"><a class="hc-toc__link" href="#sec-tests">Tests</a></li>
  </ul>
</nav>

The <li class="hc-toc__item"> wrappers are optional — the styling keys off .hc-toc__list / .hc-toc__link, so a flat list of links directly inside the nav works too.

Scrollspy (`data-hc-spy`)

Add data-hc-spy to the nav and install the behavior. It resolves each link’s #fragment to its target section, observes them with an IntersectionObserver, and marks the link of the section at the top of the viewport with aria-current="location" plus a data-active hook.

Scrollspy needs the installSpy() behavior. Install every behavior at once with import '@hypermedia-components/core/behaviors';, or just this one:

import { installSpy } from '@hypermedia-components/core';
installSpy();

installSpy() is idempotent, returns an uninstaller, and picks up navs swapped in by htmx. See Installation.

<nav class="hc-toc" data-hc-spy aria-label="On this page">
  <a class="hc-toc__link" href="#sec-inputs">Inputs</a>
  <a class="hc-toc__link" href="#sec-sql">SQL</a>
  <a class="hc-toc__link" href="#sec-tests">Tests</a>
</nav>
…
<section id="sec-inputs">…</section>
<section id="sec-sql">…</section>
<section id="sec-tests">…</section>

The behavior only tracks sections that exist, and resolves links once at install (re-install after swapping the tracked content). It never forces smooth scrolling — clicking a link is the browser’s native anchor jump — so there is nothing for prefers-reduced-motion to gate.

States

State	How it is set	Styling
Active section	`installSpy` sets `aria-current="location"` + `data-active` (or author it directly)	`--hc-toc-active-fg`, `--hc-toc-active-font-weight`, and the inline-start marker (`--hc-toc-active-marker`)
Hover	`:hover`	`--hc-toc-link-fg` → `--hc-toc-link-hover-fg`
Focus	`:focus-visible`	`2px` outline in `--hc-color-focus-ring`

The active rule matches both [aria-current="location"] and [data-active], so the highlight works whether it comes from the behavior or from server-rendered markup.

Accessibility

Label the <nav> (aria-label="On this page" or aria-labelledby) so the landmark has a name.
The active link carries aria-current="location" — the ARIA value for “the current location within a set” — which drives both the visual state and the screen-reader signal.
Without JavaScript the nav is still a working list of anchor links (no active highlight) — progressive enhancement.
Keep the focus outline; the default uses --hc-color-focus-ring to match the rest of the system.

Theming tokens

Component tokens (in component.tokens.json):

Token path	Purpose
`toc.font-size`	Text size for the whole list.
`toc.gap`	Vertical space between links.
`toc.indent`	Inline-start padding (room for the active marker).
`toc.link.fg` / `hover-fg`	Inactive link color, rest and hover.
`toc.active.fg` / `font-weight`	Active link appearance.
`toc.active.marker`	Color of the inline-start marker on the active link.

CSS variables

Show the generated CSS variables

--hc-toc-font-size | -gap | -indent
--hc-toc-link-fg | -link-hover-fg
--hc-toc-active-fg | -active-font-weight | -active-marker
--hc-color-focus-ring   (inherited from data-color)

Breadcrumb — trail from the site root to the current page.
Tabs — switch between sibling sections.