Glossary · Accessibility term
Non-interference
Non-interference is the fifth conformance requirement, and the four rules people quote from it are only its second half. The first half is about the technologies you are not relying on to meet the criteria. Those must not block access to the rest of the page, which means the page has to keep conforming while such a technology is turned on, while it is turned off, and where a user agent does not support it. Four success criteria are then added on top, and they apply to all content on the page, including content not otherwise relied upon to meet conformance. Audio that starts by itself, runs past three seconds and gives you no way to stop it or turn it down on its own. Keyboard traps. Flashing above the threshold. And moving, blinking, scrolling or auto-updating content that starts by itself and offers no way to pause, stop or hide it. None of it can be set aside, because no part of a page can be set aside from conformance at all.
In practice
These four apply to everything on the page, including content you did not write and content you are not relying on to meet anything at all. You cannot set part of a page aside, because conformance is judged on whole pages and statements about part of a page conforming cannot be made. A third-party widget that traps the keyboard breaks the page whatever you say about the widget.
The technology half of the requirement is a test you can run. Take anything on the page you are not relying on, then confirm the page still conforms with it switched on, with it switched off, and where a user agent does not support it. Switched on is the state people skip, because it sounds like the state where nothing can go wrong, and it is exactly where an optional extra traps the keyboard or flashes at everybody anyway.
They are the ones to check first in any embedded or user-generated content, because they are the ones that can make the rest of the page unusable. The one sanctioned way out works at the level of the page rather than the content on it. A page that cannot conform, such as one demonstrating a flashing hazard, is kept out of the scope of the claim entirely.
Why it matters
Plenty of rules protect somebody's ability to finish a task. These four protect the rest of the page from a single piece of content, which is why they are the ones that survive not being relied upon. Audio you cannot silence over a screen reader, a trap you cannot escape without closing the tab, flashing that causes a seizure. The technology half matters for the opposite reason, because it is what makes optional enhancement legal. You may use something assistive technology cannot work with, as long as you do not rely on it and it does not get in the way.
Not relied upon and still not allowed
An embedded third-party video that autoplays with sound, runs longer than three seconds and offers no way to stop it or turn its volume down separately fails 1.4.2 for the whole page. It fails even though you rely on nothing inside it, and it fails even if you publish a statement of partial conformance naming it, because that statement says the page does not conform. Not relying on something has never been the same as being allowed to leave it broken.
Where this shows up on the site
Related terms
- Partial conformanceA statement of partial conformance is what you publish when a page fails only because of content outside your control, such as user comments, an ad slot, or a third-party widget you cannot repair.
- ProcessA process is a series of user actions where every action is needed to finish the job, such as a checkout, a booking, or an application form.
Knowing the word is the easy part.
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