Accessibility tree - A representation parallel to the DOM that the browser builds for assistive technology; each node has a role, name, state and value.
Semantic HTML - Markup by meaning (button, nav, main, h1-h6) rather than styled div/span; role, behavior and navigation follow from it for free.
Landmark - A page region (header, nav, main, footer, aside) a screen reader uses to build a map and jump quickly between areas.
Accessible name - The name by which an element is announced to assistive technology; computed from content, a label, aria-label or aria-labelledby by an algorithm.
ARIA - Role, state and property attributes for cases where native semantics fall short; it refines rather than replaces them - the first rule of ARIA is not to use ARIA.
Live region - An aria-live area whose changes a screen reader announces without moving focus; for statuses, errors and dynamic updates.
focus-visible - The state when a focus indicator is actually needed (keyboard); it lets you keep an outline for accessibility without penalizing mouse users.
WCAG 2.2 - The W3C accessibility recommendation with A/AA/AAA levels and testable success criteria; the practical benchmark for an audit.
Crawling / indexing - A robot visiting pages and adding them to the index; the engine sees the rendered HTML and links, not the designer's intent.
Canonical - rel=canonical names the preferred URL for duplicates so search does not scatter signals across copies of one page.
Structured data - Entity markup (schema.org, usually JSON-LD) that gives the engine explicit facts about the page for rich results.
hreflang - An annotation of a page's language and regional versions so search shows the right locale; the versions reference each other reciprocally.
Logical properties - CSS properties in the inline/block axes (margin-inline, inset) instead of left/right; the interface moves to RTL without rewriting styles.
Intl - JavaScript's built-in locale-aware formatting API (dates, numbers, currency, plurals, collation) on top of Unicode CLDR data.
ICU message format - A message syntax with variables, plurals and gender; translation is not string substitution but the grammar of the target language.
lang / dir - The language and writing-direction attributes on the root and fragments; they affect speech, hyphenation, formatting and layout.