Reading this edition your way

What the edition is trying to do for you

The test this site sets itself is not whether a page can be reached but whether you can do the thinking it exists for: compare the times two observers assign to the same pair of events, choose which statistic a set of displacements should be summarised by, change a parameter and see what follows, inspect where an energy balance closes, and read a derivation step by step. Every laboratory carries a way to take those actions without dragging, without telling colours apart, without sound, and without a drawing canvas. A long description of a picture is not the same thing as being able to interrogate it.

The source German, the English translation, the explanations at four depths, every equation and every static worked example are in the page as it arrives. They do not wait on JavaScript, a fast connection, or a graphics processor.

What has been checked

WCAG 2.2 is mapped criterion by criterion in the repository, at docs/accessibility/wcag-22-map.yaml. It covers 55 criteria, 31 at level A and 24 at level AA. Of those, 46 carry a rule, the check that enforces it and the person or bead that owns it, and 9 are recorded as not applicable with a reason and the change that would make them apply again. Nothing is left undisposed. A criterion having a rule is not the same as the site meeting it, and the map is a record of intent and machinery rather than a result.

The automated checks that back those rules run as part of the ordinary test suite: 112 tests across 17 files, none failing, measured on 28 September 2026 with bun test src/testing/a11y/. They cover the contrast of every text colour in both the light and the dark theme, the name each control gives a screen reader, keyboard operation and focus order, the colours an operating system can force, and the layout at every offered combination of line length, type size and paragraph spacing. They run in Chromium and in WebKit.

What has not been checked

No round of testing with disabled readers, using their own tools, has been recorded. That is the test that counts, and until it happens the sentences above describe machinery rather than experience. The protocol for those rounds is written and waiting at docs/accessibility/manual-protocol.md; the roles that would run them, an accessibility co-design facilitator and a real-device tester, are recorded as open and recruiting alongside the project’s other independent review roles.

Automated checks are not sufficient on their own and this page does not present them as though they were. A test can confirm that a control has a name; it cannot tell you whether the name is the right one, whether the order of the page makes sense on a fourth reading, or whether an instrument can be operated by someone who is tired. The W3C’s supplemental guidance on cognitive accessibility is followed here as guidance, and no claim is made against it.

Mathematics is the part most likely to fail you, and it is checked least by machine. Each equation carries a spoken form written by hand rather than generated, because generated speech is frequently wrong for physics notation, and those forms have been read against screen readers in automated runs but not yet by a person who depends on one.

Reading preferences

The Aa button at the top of every page opens the reading preferences. Line length has three settings, type size four, paragraph spacing two, and contrast can be raised; the combinations offered are the ones tested at phone, tablet and desktop widths, and combinations that have not been tested are not offered. Reading-only stops anything that moves or loads by itself while keeping every explanation, equation and static worked example in place; it defers cost, and never removes content.

Your choices are applied before the page first appears, so there is no flash of one layout replaced by another, and they stay in your browser rather than on a server. If your browser refuses to store them they last for the session and the page still works. What is stored, and how to clear it, is set out on what this site stores.

If your system asks for reduced motion, animation stops and the current state stays on screen rather than disappearing with it. Sound never starts on its own, and nothing on the site requires hearing.

Reporting a barrier

If something here stops you, that is worth knowing about and it will be treated as a defect rather than a preference. Say what you were trying to do, the address of the page, and the browser and assistive technology you were using, through the project’s issue tracker. A report that names the action you could not complete is more useful than one that names a rule, though either is welcome.

The edition and the reasoning behind it are described on about, and the notation each paper uses, with the collisions called out, on notation.