Prefer native controls or correct ARIA roles (e.g. role="switch" + aria-checked for toggles, role="progressbar" with aria-valuenow / min / max for progress).
Icon-only buttons need an accessible name (aria-label), not only title.
Slide-over panels that trap focus use useSlideOver semantics: role="dialog", aria-modal="true", Escape to close, Tab wrap, restore focus on close.
Associate form fields with <label htmlFor> and aria-describedby for help text.
Keep document.documentElement.lang in sync with the active locale (see frontend/src/i18n.ts).
Respect prefers-reduced-motion where animations are decorative (see frontend/src/index.css and useReducedMotion in Framer Motion where used).
Modal role="dialog" nodes should have a computed accessible name (aria-label with the same string as the visible title is used on slide-overs).
Long scrollable areas use ScrollableRegion (tabIndex={0}, role="region", aria-label) so keyboard users can focus the container and scroll.
Documentation (MkDocs Material)
Theme provides landmarks, search, and keyboard navigation; avoid overrides that remove focus outlines or drop contrast below WCAG AA without a strong reason.
Figures should include meaningful alt text (or empty alt only when the image is purely decorative and the caption carries the meaning). Repository check: no bare  without description.
Card tiles (.card-link wrapping an entire feature card on the localized home pages): add an explicit aria-label in the opening <a> that states the destination (e.g. “User guide: … section”) so assistive tech does not rely on emoji/icons or horizontal rules for the link name. Keep labels in sync across docs/index.md, docs/es/index.md, docs/de/index.md, and docs/fr/index.md.
After substantive theme or CSS changes, run an automated pass on the built site (e.g. Lighthouse accessibility category or @axe-core/cli against site/ after mkdocs build) and fix regressions.
docs/stylesheets/extra.css bumps muted foreground contrast on the slate scheme and underlines in-content links so they are not identified by color alone.
docs/javascripts/scrollable-focus.js also: sets aria-label on .md-search[role="dialog"] (Material search overlay); gives nav.md-code__nav a unique aria-label per code block (copy toolbar); uses sequential, uniquearia-label strings for each scrollable code/table role="region" (with optional figure caption / table caption); subscribes to Material’s document$ stream so these fixes re-apply after instant navigation.