Robust · 4.1 Compatible
In content that uses markup, elements must have complete start and end tags, be nested according to their specifications, have no duplicate attributes, and use unique IDs, except where the specifications allow otherwise. WCAG 2.2 removed this criterion as obsolete, and a 2023 note to WCAG 2.0 and 2.1 says it should be treated as always satisfied for HTML and XML content.
Live demo
The same task, done two ways: switch between the version that passes and the one that fails, or put them side by side. Everything in the box is live, so try it with a keyboard, a pointer or a screen reader.
Compare what the screen reader preview says for the Security code field in each version.
The tools follow the version you last used.
What happened
Why it passes
Each hint has its own id, so each field is read with its own hint. The Security code field tells you to use the 3 digits on the back of the card.
Why it fails
Both hints share one id, so the browser links both fields to the first hint. On the Security code field, a screen reader user hears the hint about the 16 digits on the front of the card and may type the wrong number.
Examples
Four examples, each one running: the usual ways this criterion fails, and code that passes. Listen to them, measure them, or copy the code.
Fails
Live preview
<label for="email">Email address</label><input id="email" name="email" type="email" autocomplete="email"><label for="email">Confirm email address</label><input id="email" name="email-confirm" type="email">Both labels point at the first field, which gets both names, and the second field has no label at all. W3C's failure F77 covered duplicate ids.
Passes
Live preview
<label for="email">Email address</label><input id="email" name="email" type="email" autocomplete="email"><label for="email-confirm">Confirm email address</label><input id="email-confirm" name="email-confirm" type="email">Each id is used once, so each label names its own field. Under WCAG 2.2 this is checked as part of 1.3.1 and 4.1.2.
Fails
Live preview
<h2>Summer sale</h2><p>Sale ends <strong><em>Friday at midnight</strong></em>.</p>The em element opens inside strong but closes after it. Browsers repair this in a standard way, which is why 4.1.1 is now treated as always satisfied, but a validator still reports it.
Passes
Live preview
<h2>Summer sale</h2><p>Sale ends <strong><em>Friday at midnight</em></strong>.</p>Each element closes before its parent does, so the markup does not depend on the browser's repair rules.
Why it matters
It helped people using assistive technologies that once read a page's markup directly and could fail or report the wrong thing when the markup was broken. Browsers now repair broken HTML in a standard way and assistive technologies use the browser's accessibility tree, so problems that still matter, such as a duplicate id that gives a field the wrong label, are reported under 1.3.1 or 4.1.2 instead.
W3C: Understanding 4.1.1Level A
Level A is the minimum: failing it can shut some people out completely.
Where it is required
Still counted where the law names WCAG 2.0 or 2.1: the United States, Canada, the European Union, France, Germany, Italy, Spain, the Netherlands, Ireland, Norway, Switzerland, India, Japan and Israel. W3C now says to treat it as always met for HTML.
How to test
The steps an audit against WCAG 2.0 or 2.1 still uses. For HTML, W3C now treats it as always met.
Common failures