Add illustrations that help explain complex content
Some ideas are hard to read and easy to see. G103 asks you to put visual illustrations next to difficult text that describes a concept or a process. A chart, a diagram, a flowchart, a photograph, an annotated screenshot. They go in addition to the text, never instead of it. W3C lists this as a sufficient technique for 3.1.5 Reading Level, which is Level AAA, and we file it with the 3.1 reading and language family for the same reason. One trap is worth naming, because the technique text does not name it. A picture that carries information is non-text content, so it needs a text alternative of its own. Move meaning into a diagram with no alt text and you have solved one reader's problem by making another's.
How we find it in an audit
No tool can tell you that a passage needed a picture, so this is judgment from end to end. Our reviewers look for long procedural or conceptual writing that runs with no visual support at all. Instructions get the closest attention. So do policies and multi-step processes. Where illustrations already exist, we check that they show the concept the text describes rather than decorating the page beside it, and that each one carries alt text.
How affected users experience it
People with reading and cognitive disabilities can often work through a labeled diagram that defeats them as nine hundred words of prose. For them the illustration is not a nicety. It is the route in, and a page without one is present but unreadable. Blind readers reach the same content through a different door. That door is the text alternative on each image, which is why the two fixes have to ship together.
Passes vs. fails
Passes
Each assembly step pairs one short sentence with a labeled diagram showing which parts connect and where, and every diagram carries a text alternative describing the connections.
Fails
Instructions for assembling a crib run to 900 words of dense prose with no pictures of any kind.
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 G103: Providing visual illustrations, pictures, and symbols to help explain ideas, events, and processes. 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.