Accessibility (a11y)

The practice of designing and building digital products so that people with disabilities can perceive, understand, navigate and interact with them. "a11y" is a numeronym: "a", 11 letters, "y".

Accessible name

The short text label a browser computes for an element and exposes to assistive technology — for example, a button's visible text, an image's alt text, or a value from aria-label or aria-labelledby.

Alt text

A text alternative for an image, supplied via the alt attribute, that conveys the image's meaning or function. Decorative images take an empty alt="" so screen readers skip them.

ARIA

Accessible Rich Internet Applications: a set of HTML attributes (roles, states and properties) that describe custom widgets to assistive technology when native HTML semantics fall short. Use native elements first; ARIA cannot add behaviour, only meaning.

ARIA live region

An element marked with aria-live (polite or assertive) so screen readers announce its content changes automatically — used for status messages, alerts and dynamic updates the user did not trigger directly.

Assistive technology (AT)

Hardware or software people use to access digital content, such as screen readers, screen magnifiers, switch devices, voice-control software and refreshable braille displays.

Color contrast ratio

A measure of the luminance difference between two colours, from 1:1 to 21:1. WCAG requires at least 4.5:1 for normal text (3:1 for large text and meaningful UI components) at level AA.

Conformance level (A / AA / AAA)

WCAG's three tiers of stringency. Level A is the minimum, AA is the common legal and procurement target, and AAA is the strictest — rarely required for whole sites because some criteria cannot be met by all content.

Focus

The state of the single element that currently receives keyboard input. Only one element is focused at a time, and moving focus is how keyboard and switch users navigate a page.

Focus order

The sequence in which interactive elements receive focus as the user tabs through a page. A logical order that follows the visual and reading order preserves meaning and operability (WCAG 2.4.3).

Focus indicator

The visible outline or styling that shows which element has keyboard focus. It must be clearly perceivable; never remove it without providing an equally visible replacement (WCAG 2.4.7).

Forced Colors / High Contrast Mode

An operating-system setting that overrides page colours with a limited user-chosen palette. Detect it with the forced-colors media query and use system colour keywords so boundaries and icons stay visible.

Keyboard trap

A point where focus enters a component but cannot leave using the keyboard alone, stranding the user. WCAG 2.1.2 prohibits traps; modals must let focus out via a documented key such as Escape.

Landmark

A region of a page with a defined role — such as header (banner), nav, main, aside (complementary) and footer (contentinfo) — that lets assistive-technology users jump directly to major sections.

Modal dialog

A dialog that disables interaction with the rest of the page until it is dismissed. It should trap focus inside itself while open, restore focus to the trigger on close, and be labelled and closable by keyboard.

POUR

The four guiding principles of WCAG: content must be Perceivable, Operable, Understandable and Robust. Every guideline and success criterion sits under one of these principles.

Progressive enhancement

A strategy of building a working baseline with semantic HTML first, then layering on CSS and JavaScript. It keeps core content and functionality available even when scripts fail or are unsupported.

Reduced motion

A user preference, exposed through the prefers-reduced-motion media query, signalling that animation should be minimised or removed to avoid discomfort or vestibular triggers (WCAG 2.3.3).

Screen reader

Assistive software that converts on-screen content into synthesised speech or braille and lets users navigate by headings, landmarks, links and form controls. Examples include JAWS, NVDA, VoiceOver and TalkBack.

Semantic HTML

Using HTML elements for their intended meaning — button, nav, h1–h6, label and so on — so the browser exposes correct roles, states and relationships to assistive technology for free.

Skip link

A link, usually first in the source and visible on focus, that lets keyboard users bypass repeated blocks such as navigation and jump straight to the main content (WCAG 2.4.1).

Success criterion

A specific, testable requirement in WCAG, each assigned a conformance level (A, AA or AAA). A page conforms to a level when it meets every success criterion at that level and below.

Tab order / tabindex

Tab order is the path Tab takes through focusable elements. The tabindex attribute adjusts it: 0 adds an element to the natural order, -1 makes it focusable only by script, and positive values are discouraged.

WAI-ARIA Authoring Practices (APG)

A W3C guide that shows how to build common UI patterns — tabs, menus, dialogs, comboboxes — with the correct roles, states, properties and keyboard interactions. It is guidance, not a normative standard.

WCAG

The Web Content Accessibility Guidelines, the W3C's internationally recognised standard for accessible web content. It is organised into the POUR principles, guidelines and testable success criteria at levels A, AA and AAA.

Zoom & reflow

Zoom enlarges content for readability; reflow is the requirement that content remain usable without two-dimensional scrolling when zoomed to 400% or shown in a narrow viewport (WCAG 1.4.4 and 1.4.10).