Offer sign language versions of essential content
For many Deaf people, sign language is a first language and written text is a second one. So a signed version can be easier to follow than the same words on the page. G160 asks for sign language versions of the information, ideas and processes somebody has to understand before they can use the content. The video goes alongside the text, not instead of it, and because it is supplemental it does not have to be synchronized with anything. Embed it or link to it, either works. W3C lists this as a sufficient technique for 3.1.5 Reading Level, at Level AAA, and 3.1.5 has no advisory techniques at all. We file it with the 3.1 reading and language family for the same reason W3C ties it to reading level.
How we find it in an audit
Our reviewers identify the content people genuinely have to understand before they can act. On most sites that is a short list. Medical instructions, safety information, eligibility rules, legal terms. Then we check whether a signed version exists for those, whether it is easy to find rather than buried, and whether the sign language is the one the audience actually uses.
How affected users experience it
Reading English is not automatic for a Deaf person whose first language is a sign language, any more than reading Spanish is automatic for an English speaker. Pre-surgery instructions in dense written English are a document they have to translate under stress. A signed version delivers the same instructions in the language they think in, which changes the odds of the instructions being followed correctly.
Passes vs. fails
Passes
The same instructions are also offered as sign language videos, linked at the top as 'Watch these instructions in ASL'.
Fails
A hospital's pre-surgery instructions exist only as written English text.
Other ways to satisfy this rule
5 guides on this site are filed under 3.1.5 Reading Level. W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
This guide is our interpretation of W3C technique G160: Providing sign language versions of information, ideas, and processes that must be understood in order to use the content. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.