Glossary · Accessibility term
Relied upon
A technology is relied upon when the content would stop conforming if that technology were turned off, or if a user agent did not support it. Both halves of that test matter, because a page can survive one state and fall over in the other. Turn the script off and the tab strip you built out of it is gone. Meet a user agent that never supported it and the same thing happens for a different reason. What gets tested is a web content technology, meaning the formats and languages you author in, so HTML, CSS, JavaScript, SVG and PDF all qualify. The software people open them with does not, so a browser, a media player or a screen reader is never the thing being relied upon. The question is never whether you used something. It is whether the page still works without it.
In practice
Turning the technology off is half the test. The definition has two triggers, so check the content with the technology switched off, and then check it where a user agent does not support the technology at all. If it stops conforming in either state, that technology is relied upon, and the way you are using it has to be accessibility supported.
There is a second duty attached to the answer. Anything you provide in a way that is not accessibility supported has to be available some other way that is, so not relying on it was never the end of the job. The information still has to reach people.
Anything that comes out the other side as not relied upon gets a further test, and that one adds a third state. The page has to keep conforming with the technology turned on, with it turned off, and where a user agent does not support it. Turned on is the state people skip, and it is where an optional extra breaks the page while it is running.
Why it matters
This is the test that settles arguments about JavaScript. Script is allowed, because a technology can be used in ways that are not accessibility supported as long as it is not relied upon and the page as a whole still meets the conformance requirements. What is not allowed is relying on a way of using it that assistive technology cannot work with. And you rely on particular uses rather than on whole technologies, so "we rely on JavaScript" never answers the question on its own.
The format, not the software that opens it
A site that publishes its terms only as a PDF relies on PDF, which is a web content technology, so the way that document is built has to be accessibility supported. The reader's PDF viewer is not what is being relied upon, because a viewer is a user agent and WCAG keeps those on the other side of the line. That matters because it puts the fix on your side. Nothing forbids you from naming or supplying a viewer, and it does not reclassify anything. The file is still the thing you are relied upon for, so ship a better file.
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Related terms
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