revealjs removes the `href` from code line-number links

[cwickham]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

For revealjs, Quarto removes the href from each code line-number link (format-reveal.ts). The comment says these links "can't work because ids are used for sections". That is no longer true. Since reveal.js 5, links to element ids work (f8e3406, hakimel/reveal.js#3444).

Removing the href now causes two bugs:

1. Single file: fixEmptyHrefs (html.ts) sets href="". A click on a line number, or Enter on it, goes to the title slide.
2. Website project: fixEmptyHrefs is skipped (pandoc.ts), so the anchor has no href. The aria-label from Fix code-line-numbers links having no accessible name #14662 is then on an <a> that is not a link. axe reports aria-prohibited-attr (WCAG 4.1.2).

If the href is kept, revealjs gets the same markup as format: html: <a href="#cb1-1" aria-label="1">. I tested this by putting the href back in the rendered output. A click or Enter stays on the slide, stepped code-line-numbers highlights are not changed, and axe reports no line-number problems in either project type.

We found this with an axe scan of quarto.org: 87 instances on 7 revealjs pages, for example the revealjs demo.

Investigation was AI-assisted and grounded in a local clone of quarto-cli, per CONTRIBUTING.md's note on using AI tools.

Steps to reproduce

deck.qmd:

---
title: Deck
format: revealjs
---

## Code

```python
x = 1
y = 2
```

1. Run quarto render deck.qmd. Open deck.html, go to the "Code" slide, and click a line number.
2. Put deck.qmd in a website project (project: type: website, plus an index.qmd). Run quarto render, then quarto call axe _site --pages deck.html.

Actual behavior

1. Single file: the line anchor is <a href="" aria-label="1"></a>. The click goes to the title slide.
2. Website: the line anchor is <a aria-label="1"></a>. axe reports aria-prohibited-attr on each line anchor.

Expected behavior

Line numbers are links to their line, as in format: html: <a href="#cb1-1" aria-label="1"></a>. A click stays on the slide, and axe reports no violation.

Your environment

• IDE: Positron 2026.10.0 (build 54)
• OS: macOS 26.6.2 (build 25G83)

Quarto check output

Quarto 1.11.4
[✓] Checking environment information...
      Quarto cache location: /Users/charlottewickham/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.10.0: OK
      Dart Sass version 1.101.0: OK
      Deno version 2.7.14: OK
      Typst version 0.15.1: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.11.4
      Path: /Applications/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: v2026.04
      Chrome Headless Shell: 150.0.7871.115
      VeraPDF: 1.28.2

[✓] Checking LaTeX....................OK
      Using: TinyTex
      Path: /Users/charlottewickham/Library/TinyTeX/bin/universal-darwin
      Version: 2026

[✓] Checking Chrome Headless....................OK
      Using: Chrome Headless Shell installed by Quarto
      Path: /Users/charlottewickham/Library/Application Support/quarto/chrome-headless-shell/chrome-headless-shell-mac-arm64/chrome-headless-shell
      Version: 150.0.7871.115

[✓] Checking basic markdown render....OK

[✓] Checking R installation...........OK
      Version: 4.6.0
      Path: /Library/Frameworks/R.framework/Versions/4.6/Resources
      LibPaths:
        - /Users/charlottewickham/Library/R/arm64/4.6/library
        - /Library/Frameworks/R.framework/Versions/4.6/Resources/library
      knitr: 1.51
      rmarkdown: 2.31

[✓] Checking Knitr engine render......OK

[✓] Checking Python 3 installation....OK
      Version: 3.12.2
      Path: /Users/charlottewickham/.pyenv/versions/3.12.2/bin/python3
      Jupyter: 5.9.1
      Kernels: python3

[✓] Checking Jupyter engine render....OK

[✓] Checking Julia installation...