Glossary

Every trade abbreviates, and this one is worse than most. Here is the vocabulary the site leans on — short, honest definitions for anyone new to accessibility or to the newest CSS. Every term can be linked to directly.

a11y: Numeronym for “accessibility”: a, eleven letters, y. Making the web usable by people with disabilities — the whole point of this site.
Accessibility tree: The browser’s distilled version of the page that assistive technology actually reads: for every element that matters, a role, a name, and its current state. DevTools can show it to you.
ARIA: Accessible Rich Internet Applications: attributes that add semantics for assistive technology when native HTML can’t express them. The first rule of ARIA: prefer native HTML, which needs none.
Assistive technology (AT): Software or hardware people use to perceive and operate the web — screen readers, switch devices, magnifiers, voice control.
Baseline: The web platform’s shared support signal: “widely available” (stable in all engines for ~30 months), “newly available” (everywhere, but recent), “limited availability” (not yet in every engine). The showcase tiers borrow its exact vocabulary.
Cascade layers: @layer — named priority bands for CSS, so user-preference styles can beat component styles without !important. This site’s entire stylesheet is layered; that is the one hard rule here.
Color-vision deficiency (CVD): Reduced ability to tell certain hues apart — “color blindness”. Why meaning never rides on color alone here, and why the theme picker ships CVD-friendly presets.
Conformance level (A / AA / AAA): WCAG’s three strictness grades. AA is the common legal and contractual target; this site aims at WCAG 2.2 AA and demos a few AAA criteria on top.
Design tokens: Named values — colors, spacing, type sizes — declared once and used everywhere, so themes and user preferences re-skin the site by swapping values, not rewriting rules.
Forced colors: An OS accessibility mode (like Windows High Contrast) that replaces site colors with the user’s own palette. CSS meets it through the forced-colors media query; component boundaries must survive it.
Interop: The yearly joint project where the Chrome, Firefox, and Safari teams pick platform features and make them behave identically across all three engines — the reason “works everywhere” keeps expanding.
Landmark: A labeled page region — header, nav, main, footer — that assistive technology can list and jump between. Free structure, straight from semantic HTML.
POUR: WCAG’s four principles: Perceivable, Operable, Understandable, Robust. Every criterion in the standard hangs off one of them.
Progressive enhancement: Build the accessible baseline first, then layer richer behavior on top where the browser supports it — so missing support means a plainer page, never a broken one.
Reduced motion: A system preference (prefers-reduced-motion) asking for less animation — for people with vestibular disorders, motion is physically sickening. Here, animation is an enhancement that bows out on request.
Screen reader: Assistive technology that speaks the page aloud (VoiceOver, NVDA, JAWS), navigating by the semantics in the markup — the reason markup quality is something you can hear.
Semantic HTML: Elements that say what they are — button, nav, details, h1 — and bring keyboard behavior and assistive-tech meaning with them for free. The site’s little-to-no-JavaScript thesis rests on this.
Skip link: A link, first tab stop on the page, that jumps straight past repeated navigation to the content (WCAG 2.4.1). Press Tab once on any page here to meet one.
WCAG: The Web Content Accessibility Guidelines — the W3C standard (2.2 is current) that most accessibility law worldwide points at. Chapter 01 walks its timeline. WCAG 3.0 is a working draft, years from done, and will not replace 2.2.