hc-navmenu is a top-level site navigation whose items can open content panels (a mega-menu). It is a disclosure set: each trigger is a button[aria-expanded] controlling a popover panel anchored under it with CSS Anchor Positioning. Panels open on hover / focus, one at a time, and the links inside stay real <a> — so it works for plain MPA navigation and htmx alike.

Basic example

<nav class="hc-navmenu" aria-label="Main">
  <ul class="hc-navmenu__list">
    <li class="hc-navmenu__item">
      <button class="hc-navmenu__trigger" type="button"
              data-hc-navmenu-trigger aria-controls="nm-products">Products</button>
      <div class="hc-navmenu__panel" id="nm-products">
        <a class="hc-navmenu__link" href="/analytics">Analytics</a>
        <a class="hc-navmenu__link" href="/billing">Billing</a>
      </div>
    </li>
    <!-- A plain top-level link needs no trigger / panel. -->
    <li class="hc-navmenu__item">
      <a class="hc-navmenu__link" href="/pricing">Pricing</a>
    </li>
  </ul>
</nav>

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

installNavmenu() is idempotent and returns an uninstaller. The zero-config @hypermedia-components/core/behaviors entry auto-installs it and picks up content swapped in by htmx.

A trigger gets aria-haspopup / aria-expanded / aria-controls wired automatically; its panel becomes a popover anchored beneath it.

Behaviour

Hover / focus opens a panel after a short intent delay and closes it after a brief grace period (so moving the pointer from the trigger into the panel doesn’t dismiss it). Only one panel is open at a time.
Keyboard: ↓ / ↑ open the panel and move focus to the first / last item inside; Esc closes it and returns focus to the trigger; Tab moves through triggers and panel links normally.
Links stay links. The behavior never intercepts clicks on <a> inside a panel — navigation is the browser’s (or htmx’s, if the link carries data-hx-*).

Responsive (mobile)

On narrow screens a horizontal mega-menu doesn’t fit. Because the panels are plain markup, the same content degrades well: collapse the bar behind a toggle (e.g. inside an hc-drawer) and let each section render as a stacked hc-collapsible. Switch layouts with a media query — the links and structure are identical, so no duplicate markup is required.

Browser baseline

Primitive	Required version
HTML `popover`	Chrome 114, Edge 114, Firefox 125, Safari 17
CSS Anchor Positioning	Chrome 125, Edge 125, Firefox 147, Safari 26

Where Anchor Positioning is missing, installNavmenu() falls back to JS positioning — the panel still opens and dismisses correctly everywhere popover is supported.

Accessibility

Wrap the menu in a <nav> with an aria-label; each panel trigger is a real <button> exposing aria-expanded and aria-controls.
Panels are popovers, so Esc and outside-click dismissal come from the platform; focus returns to the trigger on Esc.
Keep panel contents as real links / buttons in source order so they are reachable by Tab and announced normally.

Theming tokens

Token path	Purpose
`navmenu.gap`	Gap between top items.
`navmenu.trigger-padding-x` / `-y`	Trigger / top-link padding.
`navmenu.trigger-radius`	Trigger / top-link radius.
`navmenu.trigger-fg`	Trigger text color.
`navmenu.trigger-hover-bg`	Trigger hover / open background.
`navmenu.panel-bg` / `-fg` / `-border`	Panel surface.
`navmenu.panel-radius` / `-padding` / `-min-width`	Panel box.
`navmenu.panel-offset`	Gap between trigger and panel.
`navmenu.link-padding-x` / `-y` / `-radius`	Panel link box.
`navmenu.link-fg` / `-hover-bg`	Panel link colors.

CSS variables

Show the generated CSS variables

--hc-navmenu-gap | -trigger-padding-x | -trigger-padding-y | -trigger-radius
--hc-navmenu-trigger-fg | -trigger-hover-bg
--hc-navmenu-panel-bg | -panel-fg | -panel-border | -panel-radius | -panel-padding | -panel-min-width | -panel-offset
--hc-navmenu-link-padding-x | -link-padding-y | -link-radius | -link-fg | -link-hover-bg

Menubar — application menu bar (actions), not site navigation.
Menu — a single dropdown action menu.
Drawer — a common host for the mobile version of a site nav.

Navigation menu