You’re (probably) doing anchor links wrong

Studying the accessibility of anchor links

June 15, 2021

I’m the original author of markdown-it-anchor, a markdown-it plugin to automatically add an id attribute to headings, and optionally add anchor links (permalinks).

There’s been some activity lately about proper accessibility of heading permalinks, and this was brought to my attention to improve markdown-it-anchor’s way of rendering permalinks out of the box.

If you want to get directly to the heart of the subject, you can jump to another take on accessible permalinks. Otherwise, I’ll start by giving a bit of backstory on the way markdown-it-anchor handles permalinks.

When I originally built this plugin back in 2015, I gave a boolean option to enable permalink generation, which would then default to a GitHub-style permalink. The markup was the following.

<h2 id="title">
  <a class="header-anchor" href="#title"></a>
  Title
</h2>

You could configure the permalink class (defaulting to header-anchor), permalink symbol (defaulting for some reason to which is actually a paragraph symbol) or provide your own renderer function where you could directly manipulate the markdown-it token stream.

I decided closely after the first release to add aria-hidden="true" to the permalink to fully mimic GitHub’s behaviour, under the premise that the permalinks weren’t relevant to screen reader users, and that GitHub was probably a good example to follow about doing the Right Thing™.

This was fine for the next couple of years, until…

First accessibility request

In 2019, we get our first accessibility issue, pointing out that using aria-hidden was incorrect here because those links would be useful to screen reader users too, and especially, accessibility linting tools were flagging them because having aria-hidden focusable elements is considered a bad practice.

This issue was opened by Zach, the author of Eleventy, a static site generator, and he patched the output of markdown-it-anchor in Eleventy to remove the aria-hidden attribute until it was fixed upstream.

Fabio, a core contributor of markdown-it-anchor, tackled that issue and removed aria-hidden from permalinks after doing some research to confirm this was the right thing to do.

First issue with the fix

Do you know that feeling when you fix a bug, only to discover it introduced at least another bug?

This is basically what happened by removing the aria-hidden attribute.

Just a few months after the fix, and this time on the Eleventy repo, an issue is opened by Oliver to point out that the permalinks are still not accessible, because they’re not keyboard focusable and don’t have an accessible name (issue which gets a PR more than a year later suggesting to add aria-labelledby).

He then suggests that markdown-it-anchor include an option to add custom attributes to the permalink, without having to write a custom renderer, and then went on and implemented the permalinkAttrs option. This allowed, for example, to configure a generic aria-label on the permalink (e.g. “heading permalink”), but we’ll see later that this is not an ideal solution either.

The hard truth

Exactly a year later, Binyamin brings back the aria-hidden topic, explaining that the default behaviour is still not accessible, because screen readers read out the permalink symbol instead of a meaningful label.

He notes that GitHub (still) sets aria-hidden="true" on the permalinks, likely to suggest that we could do the same — which would bring us back to the original behaviour. 😜

Even though I didn’t answer then, it is while reading this notification that I realized that the accessibility of permalinks was a complex topic, and that it was going to be hard, if not impossible, to satisfy everybody.

The question of accessible permalinks stayed in my mind, until…

The very simple solution

About at the same time, my friend Kitty, is switching from Jekyll to Eleventy, and finds my plugin while looking for a way to add ids to headings. 😎

Since one of Kitty’s area of expertise is accessibility, I was secretly hoping that they enabled markdown-it-anchor permalinks, so that I could learn from their implementation to make markdown-it-anchor’s default permalinks more accessible.

But it turns out that Kitty doesn’t use permalinks, only header ids.

After trying to make permalinks accessible without luck, I started to think that the best solution might be to not use them at all. With just ids, you can already link to your own titles and build a table of contents. More technical users can still inspect the page to find the ids and use them as anchors.

Sometimes, the smartest way to implement a non-standard feature, might be to… not?

Just two weeks later, Amber publishes a post about designing truly accessible anchor links.

This is an awesome article that I highly recommend reading. Amber explains the 5 iterations she went through to make accessible anchor links on her own blog, including the details of her research.

But it’s 3 months later that I hear about it, when Nicolas opens an issue on the markdown-it-anchor repo, after also writing a blog post on the subject.

That was a lot of new information for me to unpack, but I was really happy to see some updates on this topic which had long been an unanswered question in my mind.

Sadly that solution was a bit more complex than what I hoped, in a way that would require configuration from markdown-it-anchor’s perspective, making it unsuitable as a default. While it’s one of the best solutions from an accessibility point of view, the implementation affects other aspects of the permalink and headings, including browsers “reader mode”, RSS readers, SERP, and adds extra challenges about internationalization.

Nicolas tweeted about this to gather more insights on the subject, which brought quite some activity on the tweet as well as the GitHub issue, with high quality suggestions from Kitty, Amber, as well as Barry and Thierry who both dug in depth on the alternative solution of turning headers themselves into links (the style used by MDN and Web Almanac). They also found creative ways of making the markup of header links behave like the original implementation, so be sure to checkout the GitHub issue to find out about all of this!

Conclusion #0: no one solution can satisfy all users

This discussion made me realize that until there is a standard and native way of implementing anchor links, no solution is going to satisfy all users.

As we saw with the various accessibility issues opened on markdown-it-anchor and Eleventy as we tweaked the markup in the past, what one user will consider a fix will be a bug for another one. A solution might meet one user needs, but at the cost of other aspects that a different person will find important.

There is no silver bullet, and you probably won’t even have a consensus from screen reader users, especially when their experience and habits vary based on their browser and assistive technology of choice. What’s important is to come to a solution that makes it possible for people to link to a specific title of an article, without it being a chore.

Kitty Giraudel, March 1, 2021

Because of this, I switched my goal from finding a single bulletproof solution, to giving more visibility to all the available solutions that were identified and carefully analyzed, explaining their pros and cons, so that markdown-it-anchor users can make an educated choice on what suits their website and audience best.

Conclusion #1: no default is better than a bad default

The absolute default (and main purpose) of markdown-it-anchor is to automatically add an id attribute on headings. Adding permalinks is an option, and doesn’t need a default.

Since I realized that no single default would make everybody happy, and it’s not essential to have one for this option anyway, I decided to modify the API to require explicit configuration of the permalink behaviour if it is going to be enabled.

This makes sure that the user reads about the existing options and their tradeoffs, so they explicitly chose the one that makes the most sense to them.

While utopically it would have been nice to make every markdown-it-anchor user’s permalinks accessible with a npm update, we don’t have a single solution that suits every use case and wouldn’t break existing markup and styling, so this is not a realistic option.

Final implementation

I made a pull request that deprecates the permalink: true way of using a default (poorly accessible) renderer, and instead made the permalink option accept a function to render the permalink (previously called renderPermalink).

Additionally, I provided a number of built-in renderers, documenting their upsides and caveats. All of this can be found on the project’s repo, and it’s part of the 8.0.0 release. Here’s an overview of what was added.

md.use(anchor, {
  permalink: anchor.permalink.headerLink()
})
<h2 id="title">
  <a class="header-anchor" href="#title">Title</a>
</h2>

This was one of my favorite solutions that came out of the discussion, because it’s the simplest one. You can see it used on the MDN as well as HTTP Archive and their Web Almanac, and is the one I chose to use on this blog as well.

The main problem with this kind of permalink is that you cannot include links inside headers, since they’re already a link.

It’s also not as widespread as other patterns, which might confuse some users, and it makes it harder to select parts of the header text (I only learnt during that discussion that you can use Option (macOS) or Alt to partially select any link text, so this is probably not common knowledge) but you can use some tricks to make that markup look and feel like other more recognized implementations.

Keep in mind that this pattern currently breaks reader mode in Safari, an issue you can also notice on the referenced websites above. This was already reported to Apple but their bug tracker is not public.

md.use(anchor, {
  permalink: anchor.permalink.linkAfterHeader({
    style: 'visually-hidden',
    assistiveText: title => `Permalink to “${title}”`,
    visuallyHiddenClass: 'visually-hidden'
  })
})
<h2 id="title">Title</h2>
<a class="header-anchor" href="#title">
  <span class="visually-hidden">Permalink to “Title”</span>
  <span aria-hidden="true">#</span>
</a>

This is the solution proposed by Amber and Nicolas, and backed by Kitty. It’s the one that arguably provides the clearest experience in screen readers.

Note that making sure that the assistive text contains the title is important here:

Regarding anchor link text, you can’t use just “Link to this section” because screen reader users often ask for the list of links in the page (they also ask for the list of headings), and they would get multiple times the same “Link to this section”.

Nicolas Hoizey, March 1, 2021

The downsides are that it requires a bit more effort to style and localize, causes the visually hidden text to show in SERP and RSS readers, and adds extra padding below headers in reader mode. Not bad, considering.

ARIA hidden

md.use(anchor, {
  permalink: anchor.permalink.ariaHidden({
    placement: 'before'
  })
})
<h2 id="title">
  <a class="header-anchor" href="#title" aria-hidden="true">#</a>
  Title
</h2>

Finally, this is the GitHub inspired way of implementing permalinks, and legacy default of markdown-it-anchor. It needs little to no extra styling and behaves in the way most users will expect out of the box, but it’s explicitly made inaccessible.

This might or might not be an issue for you, but it’s definitely worth thinking about, and considering the options above instead.

Try it with a screen reader yourself!

Are you wondering if the experience on your website is accessible to screen reader users? Reading about accessibility is great, but nothing can teach you as much as actually using a screen reader.

This was much easier than I expected, at least on macOS. The system ships with VoiceOver, which you can turn on by pressing Command + F5. I recommend using it in Safari as I’ve found the behaviour to be more quirky in other browsers.

We saw earlier that “screen reader users often ask for the list of links in the page”, as well as the list of headings.

According to a WebAim survey from 2014, two-thirds of screen reader users scan headings as the first step of trying to find information on a long web page, so this should stay clean and intact above all.

Kitty Giraudel, March 1, 2021

In VoiceOver, you can open the “rotor” by pressing Caps Lock + U, which allows you to list all the links and headings of the page. You can browse through the lists by using the arrow keys. Make sure that those are usable on your website!

Final word

As a newbie to the topic of accessibility, it was wonderful getting to learn from many knowledgeable peers who documented that aspect of anchor links, and contributed to the discussion in markdown-it-anchor’s related issue and on Twitter.

Shoutout to Amber, Nicolas, Kitty, Barry and Thierry for taking the time to research this issue and sharing their findings!

Finally, if I said anything wrong or inaccurate in this post, please let me know, I’ll be more than happy to fix mistakes and integrate improvements!