The people
And everyone, sometimes: a broken arm, bright sunlight, a phone held in one hand on a bus, a noisy room, a trackpad that has stopped working. Accessibility is not a minority feature; it is the difference between a product that copes with real conditions and one that assumes a perfect user.
| Roughly | What breaks a page | |
|---|---|---|
| Blind or low vision | 2–3% of adults | unlabelled controls, images with no alt, a page that cannot be zoomed |
| Motor impairment | 5–8% | anything that needs a mouse, small targets, a keyboard trap |
| Deaf or hard of hearing | 5% | video with no captions, audio-only information |
| Cognitive, including dyslexia | 10%+ | dense text, no structure, timeouts, moving content |
| Colour blindness | 8% of men | meaning carried by colour alone |
What it actually is
A page is accessible when the information and the operation survive being presented differently: read aloud in a different order, magnified four times, navigated with a keyboard only, rendered with your colours ignored, used with a voice command.
That is why semantics matter so much. A screen reader does not see your layout; it walks a tree of roles and names. If a control is a div with a click handler, there is nothing in that tree to walk.
The standard, in one paragraph
WCAG is the reference, in three levels: A (essential), AA (the practical target and what laws point at), AAA (specific contexts). It is organised under four principles — Perceivable, Operable, Understandable, Robust — which are a genuinely useful checklist when a decision is not covered by a rule.
Most legislation, including the EU's European Accessibility Act, the UK's Equality Act, the ADA in the US and Section 508, points at WCAG 2.1/2.2 level AA. Public-sector sites in most of Europe have been required to meet it for years, and the EAA extended much of it to consumer services in 2025.
AA is achievable in ordinary work if it is done as you build. Retro-fitting it to a finished product costs several times more, which is the entire argument for reading this course before the redesign rather than after the complaint.
The curb-cut effect
Dropped kerbs were built for wheelchairs. They are used by prams, delivery trolleys, suitcases and anyone carrying something heavy — far more often than by the group they were mandated for.
Captions are used on trains and in open-plan offices. Keyboard support is what power users want. Clear labels help everyone in a hurry. High contrast helps in sunlight. Good structure is what search engines read. Every item in this course pays for itself twice.
What this course checks
Each lab runs against the browser's real DOM, with a small engine that computes the two things you cannot otherwise see from JavaScript: the accessible name an element ends up with, and the contrast ratio between two colours. The name computation is tested against Chromium's own accessibility tree — where the two disagree, the browser is right.
What no automated check can tell you is whether the name is sensible, whether the reading order makes sense, or whether the thing is usable. That is the last lesson, and it involves turning a screen reader on.