Accessibility and the Semantic Web (2 Part Series)
We all love our
<div> tags. They've been around for decades, and for decades they've been the go-to element when you need to wrap some stuff in a block for styling or structural purposes. It's still very common to look through production websites and see stuff like this:
<div class="container" id="header"> <div class="header header-main">Super duper best blog ever</div> <div class="site-navigation"> <a href="/">Home</a> <a href="/about">About</a> <a href="/archive">Archive</a> </div> </div> <div class="container" id="main"> <div class="article-header-level-1"> Why you should buy more cheeses than you currently do </div> <div class="article-content"> <div class="article-section"> <div class="article-header-level-2"> Part 1: Variety is spicy </div> <!-- cheesy content --> </div> <div class="article-section"> <div class="article-header-level-2"> Part 2: Cows are great </div> <!-- more cheesy content --> </div> </div> </div> <div class="container" id="footer"> Contact us! <div class="contact-info"> <p class="email"> <a href="mailto:email@example.com">firstname.lastname@example.org</a> </p> <div class="street-address"> <p>123 Main St., Suite 404</p> <p>Yourtown, AK, 12345</p> <p>United States of America</p> </div> </div> </div>
Hoo, that's a lot of
<div>s. And hey, it works. I mean, mostly. It has the structure you need, and I'm sure it'll look the way you intend by the time you're done styling it. But it has some big problems:
Accessibility - Many a11y tools are pretty smart, and try their best to parse the structure of a page to help guide users through it in the way the page's author intends, and to give users easy jump points to navigate quickly to the section of the page they care about. But
<div>s don't really impart any useful info about the structure of a document. The smartest a11y tool in the world still ins't a human, and can't be expected to parse
idattributes and recognize all the weird and wild ways that devs all over the world name their blocks. I can recognize that
class="article-header-level-2"is a subheading, but a robot can't. (And if it can, get it out of my computer, I'm not ready for the AGI revolution just yet.)
Readability - To read this code, you need to carefully scan for the class names, picking them out from between the
<div class="..."></div>boilerplate. And once you're a few levels deep in the markup, it becomes tricky to keep track of which
</div>closing tags go with which
<div...>opening tags. You start to rely very heavily on IDE features like coloring different indentation levels or highlighting the matching tag for you to keep track of where you are, and in larger documents it can require a lot of scrolling on top of those features.
Consistency and standards - It can be frustrating to start a new job or move to a new project and have to learn from scratch all the crazy markup conventions used across the codebase. If everyone had a standardized way to mark up common structures in web documents, it would be much easier to skim an HTML file in an unfamiliar codebase and get a quick handle on what it's supposed to represent. If only there was such a standard...
HTML5 is not new. That's an understatement; an initial working draft was released for public comment in January of 2008 (11 years ago!), and it became a full-fledged W3C recommendation in October of 2014, 4½ years ago. So, like, it's been around for a while.
One of the primary advancements of HTML5 was introducing a standardized set of semantic elements. The term "semantic" refers to the meaning of a word or a thing, so "semantic elements" are elements designed to mark up the structure of a document in a more meaningful way, a way that makes it clear what they're for, what purpose they serve in the document. And importantly, since they're standardized, these elements define the document in a way that everyone can use and understand, robots included.
I think the HTML5 spec itself sums up the issue nicely in a note under the definition of the
Authors are strongly encouraged to view the div element as an element of last resort, for when no other element is suitable. Use of more appropriate elements instead of the div element leads to better accessibility for readers and easier maintainability for authors.
I'll divide the semantic block elements into two categories: primary structure and content indicators. These aren't standard terms or anything; I just made them up for this article. But I think the distinction is useful enough. 🤷♂️
There's a super common pattern that can be found in websites, tutorials, and even CSS libraries all over the internet, and for good reason. We often divide a page at its topmost level into three regions: header, main, and footer, then divide those regions into sections as needed. I included this in my example above to prove the point:
<div class="container" id="header">...</div> <div class="container" id="main"> ... <div class="article-section">...</div> ... </div> <div class="container" id="footer">...</div>
I've seen (and used) this pattern for decades, and it makes a ton of sense to structure a document this way, both for readability of the HTML and for easier styling of the page in CSS. The header and footer elements also make partial templates in languages like PHP or Rails/ERB a ton easier to work with, as you can include common header and footer partials all over the site:
<?php include 'header.php'; ?> <div id="main">...</div> <?php include 'footer.php'; ?>
So here's the thing: everyone agrees that this is a nice pattern to follow. And that includes the folks at the WHATWG and W3C, who standardized the pattern into four new elements in HTML5 with very clear names:
<footer> elements are basically twins: they're very similarly defined in the spec and follow the same set of rules about where they're allowed to be used, with the only difference being their semantic purposes: headers go at the beginnings of things, footers go at the ends of things. And by "things", I mean more than just the
<body> of your page: this pair of elements are designed to be used within any part of your document that represents a chunk of content with a clear beginning and end. This can include things like forms, articles, sections of articles, posts on a social media site, cards, etc.
Headers and footers are attached semantically to the closest "sectioning root" or "sectioning content" element. These are things like
<aside>, and lots of others; click the links above if you want the full lists. Assistive technologies can use these elements and others to generate an outline of a document, which can help users navigate it more easily. You shouldn't have more than one
<footer> per sectioning root/content. (One of each is fine, but not two of the same.)
As a final note,
<header>s very often hold the heading element (
<h6>) for their context. This is not necessary, but can help to group other related elements with the heading, like links, images, or subheadings, and can help maintain a consistent structure even when the heading is the only element in the
The third primary region element,
<main>, is special. The spec says two very important things about
The main content area of a document includes content that is unique to that document and excludes content that is repeated across a set of documents such as site navigation links, copyright information, site logos and banners and search forms (unless the document or application’s main function is that of a search form).
<main> is where you put the good stuff, the important parts of a page, the reason the user came to this page in particular, not your site in general. In other words, the main content. 😯😲🤯
All that other stuff, logos and search forms and navigation and such, can go in a
<footer> within the
<body> but outside of
There must not be more than one visible main element in a document. If more than one main element is present in a document, all other instances must be hidden using the hidden attribute.
This is pretty unique. Unlike
<footer> (and most other block elements),
<main> can't be used all over the page within arbitrary sectioning content; it should be used once and only once. Or rather, it can be used multiple times in a document, but only one
<main> element should be visible at a time; all others must be hidden with the
hidden attribute, which basically acts like
display: none; in CSS. If you think about it, this suggests a pretty useful pattern for preloading views in an app: create a new
<main hidden>, fetch some content that the user is likely to view next (e.g., the next article in a series, the next slide in a slideshow, etc.), and when the user clicks the link/button to load that view, swap out the current
<main> with the preloaded one by toggling the
hidden attribute on both.
Before continuing, let's pause and review the example from above. Here's how it would look if we used
<footer> for the main structure of the article:
<header> <h1>Super duper best blog ever</h1> ... </header> <main> <h2>Why you should buy more cheeses than you currently do</h2> ... </main> <footer> Contact us! <div class="contact-info">email@example.com</div> </footer>
That's so much nicer already! But there's still plenty of work to do.
So we've got a basic outline for our page: a header, a footer, and a main content region. Now it's time to add some of that sweet, sweet content.
Typically you'll want to break your content down into sections, especially for mass text content like this article, because no one likes reading impenetrable walls of text.
<section> comes in. This one is the simplest in terms of rules: structurally speaking, it's basically just a
<div> with special semantic meaning. A
<section> begins a new "sectioning content" region, so it can have its own
What's the difference, then, between a
<section> and a regular old
<div>, and when should you use each? Well, allow me to quote the spec once again:
<section>element is not a generic container element. When an element is needed only for styling purposes or as a convenience for scripting, authors are encouraged to use the
<div>element instead. A general rule is that the
<section>element is appropriate only if the element’s contents would be listed explicitly in the document’s outline.
You know, as a quick aside, the HTML5 spec is actually pretty readable. It's one of the more readable specs out there. Every time I glance at it for a quick answer, I inevitably learn something unexpected and useful, especially if I start clicking links. Give it a try some time!
So in short, if you would list this portion of the document in the table of contents, use a
<section>. If not, use a
<div> or something else.
Okay, so we've got a solid structure for our page. Instead of just slinging
<div>s all over, we've explicitly marked the main content region of the page, and we've called out headers, footers, and sections. But there's definitely more semantics than that to our document.
Let's talk about a few of the elements added in HTML5 that communicate content semantics rather than structure.
<article> element is used to represent a fully self-contained region of content, something that could be plucked out of your page and dropped into another and still make sense on its own. This might be a literal article or blog post, but could also be used for a social media post like a tweet or a Facebook wall post.
The HTML5 spec recommends that articles always have a heading that identifies what it is, ideally using a heading element (
<article> can also have
<section> elements, so you really could use it to embed a full document fragment with all the structure it needs within another page.
To return to the example from the way up above, let's rewrite the
class="article-*" elements using an
<article> and some of the other elements we've discussed.
<article> <header> <h1>Why you should buy more cheeses than you currently do</h1> </header> <section> <header> <h2>Part 1: Variety is spicy</h2> </header> <!-- cheesy content --> </section> <section> <header> <h2>Part 2: Cows are great</h2> </header> <!-- more cheesy content --> </section> </article>
Isn't that a ton more readable than the original? And again, not only is it easier to read, it's way more useful for assistive tech; robots can't always figure out your specific class name pattern, but they can follow this structure.
This element is a bit more well-known than others.
<nav> is designed to clearly identify the main navigation blocks on the page, the groups of links that help the user find their way around the rest of the site (e.g. a site map or list of links in the header) or the current page (e.g. a table of contents).
In our example up top, let's apply a
<nav> to that group of links in the header.
<nav> <a href="/">Home</a> <a href="/about">About</a> <a href="/archive">Archive</a> </nav>
Doesn't change the structure at all, but you know what it is at a glance rather than needing to read and process the class name on a
<div> to figure it out, and more importantly the robots can find it too.
The last element we'll discuss is
<address>. This element is intended to call out contact info, and it's often used in the main page
<footer> to markup the mailing address, phone number, customer service email address, etc. for a business.
Interestingly, the rules for how to markup the content within an
<address> element is left open. The spec mentions that there are several other specs that address this, and it probably is outside the scope of HTML itself to provide that level of granularity.
A common solution is RDFa, also a W3C spec, which uses attributes on tags to label the different components of data. Here's what the footer from our example might look when marked up with
<address> elements and RDFa:
<footer> <section class="contact" vocab="http://schema.org/" typeof="LocalBusiness"> <h2>Contact us!</h2> <address property="email"> <a href="mailto:firstname.lastname@example.org">email@example.com</a> </address> <address property="address" typeof="PostalAddress"> <p property="streetAddress">123 Main St., Suite 404</p> <p> <span property="addressLocality">Yourtown</span>, <span property="addressRegion">AK</span>, <span property="postalCode">12345</span> </p> <p property="addressCountry">United States of America</p> </address> </section> </footer>
RDFa is admittedly a bit verbose, but it's pretty handy for marking up data. If you're interested in learning more about RDFa, here's a few links:
- The W3C's RDFa primer
- A description of schemas and links to a bunch of them on schema.org
LocalBusinessschema used above
Okay, we've covered a lot, and we've seen a lot of it applied to our example in bits and pieces. But let's put it all together and see what it looks like.
<header> <h1>Super duper best blog ever</h1> <nav> <a href="/">Home</a> <a href="/about">About</a> <a href="/archive">Archive</a> </nav> </header> <main> <article> <header> <h1>Why you should buy more cheeses than you currently do</h1> </header> <section> <header> <h2>Part 1: Variety is spicy</h2> </header> <!-- cheesy content --> </section> <section> <header> <h2>Part 2: Cows are great</h2> </header> <!-- more cheesy content --> </section> </article> </main> <footer> <section class="contact" vocab="http://schema.org/" typeof="LocalBusiness"> <h2>Contact us!</h2> <address property="email"> <a href="mailto:firstname.lastname@example.org">email@example.com</a> </address> <address property="address" typeof="PostalAddress"> <p property="streetAddress">123 Main St., Suite 404</p> <p> <span property="addressLocality">Yourtown</span>, <span property="addressRegion">AK</span>, <span property="postalCode">12345</span> </p> <p property="addressCountry">United States of America</p> </address> </section> </footer>
If you ask me, that's 100x more readable than the original example, and it's going to be 100x more effective for SEO and accessibility purposes, too.
These are by no means the only semantic elements in HTML. There are lots of additional elements that help to tag and structure your text content, embedded media, etc. Here are a few to check out if you're enjoying this and want to dig deeper. You might recognize a few:
And that's just a start! Like I said, when you start reading the HTML spec, it's tough to stop. It's an incredibly rich language, and I think people underestimate it a little too often.