Give every website and book nav landmark a distinct, localizable label

[cwickham]

Description

Closes #14376.

Website and book pages emit up to six <nav> landmarks. Before this PR, only the breadcrumbs had a label, and it was hardcoded English (aria-label="breadcrumb"). Assistive technology listed the rest as identical "navigation" entries, and axe flagged the pages under landmark-unique.

This PR gives each landmark a distinct label from a new set of language keys:

Landmark	Label
Navbar	navigation-main-label ("Main")
Sidebar	Adaptive: "Main" when the site has no navbar, "Section" when it has one
Secondary/mobile nav strip	navigation-secondary-label ("Secondary")
Previous/next page nav	navigation-page-label ("Page")
Breadcrumbs (both copies)	navigation-breadcrumbs-label ("Breadcrumbs")
Table of contents	aria-labelledby on its existing localized heading ("On this page") — no new key

Authors can override any key with language: metadata, per document or site-wide.

Label wording

The default labels do not contain the word "navigation". Screen readers announce the landmark role after the label, so a label like "Main navigation" reads as "Main navigation, navigation". The ARIA Authoring Practices Guide says not to use the role as part of the label, and the WAI page-structure tutorial uses the bare label "Main" for a nav region. VoiceOver testing confirmed the double announcement with the longer wording.

Design notes

• The two breadcrumb copies share one label. They hold identical links, and only one is in the accessibility tree at a time (one shows at lg and up, the other below). The APG also asks identical navigation sets to share a label.
• The secondary nav keeps a label distinct from the sidebar. Both are visible together when the mobile sidebar is open.
• The TOC label reuses the visible heading via aria-labelledby, which is the pattern the WAI tutorial recommends. The TOC nav can also hold the Other Formats / code-links / other-links sections. The label stays acceptable: everything in that nav is page-scoped.
• The TOC change also applies to revealjs (same partial pattern, toc-slide.html).

Out of scope

• Dashboard header nav: a11y: dashboard header nav landmark has no accessible name #14809
• Listing pagination label: a11y: listing pagination aria-label is not localizable #14810
• Several <a> elements carry an invalid role="navigation" (secondary-nav toggles, sidebar section toggles). Unchanged here; to be filed separately.

Documentation

No documentation PR: the only user-facing change is the new language keys, and the docs already refer users to _language.yml itself as the reference for available keys (Document Language).

Testing

• New smoke-all tests assert every label, the adaptive sidebar branch (with and without navbar), a language: override, and a custom toc-title in both html and revealjs.
• Verified axe landmark-unique passes on navbar-only, sidebar-only, navbar+sidebar, and book sites, at desktop and narrow viewports, including with the mobile sidebar open. Also reviewed the in-page report from axe: output: document on the rendered site. These browser checks were manual; this PR does not add a Playwright case for them.
• Verified the VoiceOver landmark rotor lists each landmark with a distinct name.

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes
• updated the appropriate changelog in the PR
• ensured the present test suite passes
• added new tests
• created a separate documentation PR in Quarto's website repo and linked it to this PR

AI-assisted PR

• AI tool used: Claude Code
• Codebase grounding: local clone
• Human review: I have reviewed, tested, and verified the AI-generated content before submitting.

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