Add a plain-language summary of complex content
Some content cannot be simplified without losing what it says. A policy, a diagnosis, a contract. G86 keeps the original and adds a short summary next to it, written to be understood without advanced reading ability. W3C files it as sufficient for its reading-level rule, which is Level AAA and asks that content demanding more than lower secondary reading ability be supplemented rather than replaced. So the summary does not water anything down. It sits alongside, carries the most important ideas in shorter sentences and commoner words, and lets a reader decide whether to go further. Measuring it is part of the technique rather than an optional extra, because a summary written by the person who wrote the original tends to inherit the original's habits.
How we find it in an audit
Dense pages get identified first, and dense means legal, medical, financial or technical content where a reader has something at stake. Where a summary exists, a reviewer reads it against the original and asks two questions. Whether it carries the important points rather than the easy ones, and whether it is genuinely simpler when measured rather than when skimmed. A summary that repeats the original's vocabulary in shorter sentences has done half the work and claimed all of it.
How affected users experience it
This serves readers with cognitive and learning disabilities, and it serves a far larger group nobody counts, which is everybody reading something that matters while stressed, tired or in a hurry. A summary at the top lets a reader take the key points and stop, or take the key points and keep going with something to hold the detail against. The original stays exactly as it was, so nothing is lost for the reader who needs the precise version.
Passes vs. fails
Passes
In short leads the page. Five plain sentences cover what is covered, what is not, and what it costs, before the full policy starts.
Fails
An insurance policy page opens with 1,400 words of nested clauses, so understanding it is the price of getting in.
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 G86: Providing a text summary that can be understood by people with lower secondary education level reading ability. 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.