Glossary

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Luminance(also: Relative Luminance)

The relative brightness of a color as perceived by the human eye, measured on a scale from 0 (black) to 1 (white). In accessibility, relative luminance is the foundation of WCAG color contrast ratio calculations, which compare the luminance of foreground text against its…

Lynx

A text-only web browser that runs in terminal or command-line environments, displaying web content as plain text without images, JavaScript, or visual formatting. Developed in 1992 at the University of Kansas, Lynx was historically significant for web accessibility because its…

Markup Language

A system of annotations or tags embedded within text that define the structure, presentation, or semantics of content without being displayed as visible text themselves. In web accessibility, markup languages such as HTML, XML, ARIA, and SVG are fundamental because assistive…

MathML(also: Mathematical Markup Language)

A W3C standard XML-based markup language for describing mathematical notation and its structure, enabling mathematical content to be rendered visually in web browsers and read aloud by screen readers. MathML is essential for STEM accessibility because it encodes both the visual…

Mathematical Accessibility(also: Math Accessibility, STEM Content Accessibility)

The practice of making mathematical content — including equations, formulas, graphs, and notation — perceivable, operable, and understandable by people with disabilities. Mathematical content poses unique accessibility challenges because it is inherently spatial and symbolic,…

Metadata Repository(also: Metadata Store, Metadata Registry)

A server-side system that stores and serves descriptive data about other resources — in accessibility contexts, typically information about web pages or their elements that helps assistive technology render them more usably. A metadata repository lets multiple tools share the…

Microscopic Navigation(also: Within-Page Navigation, Page-Level Navigation)

The process by which screen reader users navigate through individual elements and content within a single web page to find relevant information, as distinct from site-wide navigation between pages. Microscopic navigation involves detecting relevant content and skipping…

Microsoft Active Accessibility(also: MSAA, Active Accessibility)

Microsoft Active Accessibility (MSAA) is an accessibility API introduced by Microsoft in 1997 that enables assistive technologies such as screen readers to interact with user interface elements in Windows applications. MSAA provides a standardized way for applications to expose…

Mobile Web Accessibility(also: Mobile Accessibility)

The practice of ensuring websites and web applications are usable by people with disabilities when accessed through mobile devices such as smartphones and tablets. Mobile web accessibility presents unique challenges including small screen sizes, touch-based interaction, device…

Modal Dialog(also: Modal Window, Dialog Box)

A user interface element that appears on top of the main content and requires user interaction before returning to the underlying page. In accessibility, modal dialogs must properly manage keyboard focus—trapping focus within the dialog so screen reader and keyboard users cannot…

Moodle

An open-source learning management system (LMS) used worldwide by universities, schools, and workplaces for course delivery, assessment, and content hosting. Moodle supports accessibility through themes that meet WCAG, an Accessibility Toolkit plugin for content checking, and an…

Multilingual Accessibility(also: Multilingual Web Accessibility)

The practice of ensuring that web content and digital services are accessible to people with disabilities across multiple languages and cultural contexts. Multilingual accessibility sits at the intersection of web accessibility and web localization, recognising that translated…

Multilingual Web(also: Multilingual Website, Multi-language Web)

Web content that is available in more than one language, typically through localization of an original website into additional language versions. Multilingual websites present unique accessibility challenges because the localization process can introduce or remove accessibility…

MutationObserver(also: DOM Mutation Observer, Mutation Records API)

An HTML5 browser API that monitors and reports changes to the Document Object Model (DOM) structure of a web page in real time, including additions and removals of elements, attribute changes, and text modifications. For accessibility, MutationObserver is significant because it…

National Accessibility Portal(also: NAP, South African National Accessibility Portal)

A South African government-supported web portal developed by the Meraka Institute (CSIR) to provide accessible information sharing for the disability sector. The NAP was designed from inception as an accessible platform, featuring alternative CSS stylesheets for different font…

National Transition Strategy (NTS)(also: NTS, Web Accessibility National Transition Strategy)

The Australian Government's National Transition Strategy was a formal policy established in June 2010 requiring all federal, state, and territory government websites to conform to WCAG 2.0. It set staged milestones — Level A conformance by December 2012 and Level AA by December…

Navigability(also: Ease of Navigation, Web Navigability)

The ease and efficiency with which a user can move through a web page, application, or document to reach their intended content. For accessibility practice, navigability is a primary determinant of whether a screen-reader, voice-browser, or keyboard-only user can actually…

Near-Duplicate Pages(also: ND Pages, Near-Duplicate Web Pages)

Near-duplicate pages are web pages that belong to the same functional state from a testing perspective but exhibit low visual or structural similarity due to dynamic content differences. Common causes include dynamically loaded data, dynamically generated HTML attributes such as…

Non-Visual Skimming(also: Aural Skimming, Accessible Skimming)

Non-visual skimming is the process of quickly surveying and extracting key information from text content without visual access, typically through auditory means such as screen readers. While sighted users skim by rapidly scanning text with their eyes, blind users lack an…

Non-Visual Web Access(also: Non-Visual Browsing, Nonvisual Web Access)

The use of the web without relying on visual display, typically through screen readers, voice browsers, or refreshable braille displays that convert web content into speech or tactile output. Non-visual web access depends heavily on proper semantic HTML, alternative text for…

Non-Visual Web Browser(also: Self-Voicing Browser, Audio Web Browser, Talking Browser)

A web browser specifically designed for users who cannot see the screen, providing audio-based or haptic interfaces for navigating and interacting with web content. Unlike standard screen readers that overlay existing visual browsers, non-visual browsers are purpose-built to…

Nonvisual Access(also: Non-Visual Access, Nonvisual Web Access, Non-Visual Web Access)

The use of digital content, particularly web pages and applications, through means other than sight. Nonvisual access typically involves screen readers that convert text to speech, braille displays that render content tactilely, or other assistive technologies that present…

On Input(also: WCAG 3.2.2)

WCAG 2.1 success criterion 3.2.2 (Level A) requires that changing the setting of any user interface component does not automatically cause a change of context (e.g., submitting a form, navigating to a new page, or moving focus to another component) unless the user has been…

Online Accessibility Act(also: OAA, US Online Accessibility Act)

A proposed US federal law (H.R. 1100, introduced in the 117th Congress) that would require consumer-facing websites and mobile apps of covered organisations to comply with Web Content Accessibility Guidelines (WCAG). The OAA is intended to close an ambiguity in the existing…

Online Braille(also: Web Braille, Digital Braille, Electronic Braille)

Online Braille refers to Braille content that is generated, distributed, or accessed through the Internet or digital platforms, as opposed to traditional embossed paper Braille. This includes web-based Braille translation services, downloadable Braille-formatted files such as…

Opportunistic Accessibility(also: Opportunistic Accessibility Improvement)

Opportunistic accessibility is an approach to improving digital accessibility in which enhancements are automatically applied to the maximum extent possible without causing negative side effects. Rather than treating accessibility as an all-or-nothing goal, opportunistic…

Overlay Fact Sheet(also: Accessibility Overlay Fact Sheet)

A public document signed by over 600 accessibility experts, lawyers, and contributors to web accessibility guidelines that critically evaluates the claims made by accessibility overlay vendors. The fact sheet argues that overlays do not adequately address the needs of disabled…

POUR Principles(also: POUR, Four Principles of Accessibility)

The four foundational principles of the Web Content Accessibility Guidelines (WCAG): Perceivable, Operable, Understandable, and Robust. Perceivable means information must be presentable in ways users can perceive (e.g., alt text for images, captions for video). Operable means…

Page Fragmentation(also: Visual Fragmentation, Content Fragmentation)

A web accessibility problem where different types of content on a web page (news articles, advertisements, navigation menus, related links) are visually grouped using colours, spacing, images, and layout but lack structural markup that would allow non-visual users to identify…

Page Landmarks(also: ARIA Landmarks, Landmark Regions, Landmark Roles)

Named regions of a web page that identify its high-level structure — for example banner, navigation, main, complementary, search, form, contentinfo — so that assistive technology can expose them as jump targets. Landmarks are typically declared with semantic HTML elements…

Page Linearization(also: Content Linearization, DOM Linearization, Source Order)

The process by which screen readers and other assistive technologies present web page content as a sequential, one-dimensional stream of text, typically following the order of elements in the HTML source code. Since web pages are designed as two-dimensional visual layouts where…

Page Magnification(also: Page Zoom, Web Page Magnification)

An accessibility feature that enlarges the entire visual presentation of a web page, including text, images, and layout elements, to make content easier to see for people with low vision or visual fatigue. Unlike text-only size increases, page magnification scales all page…

Page Sampling(also: Page Selection Strategy, Website Sampling)

The methodology used to select which pages within a website will be evaluated during an accessibility assessment. Common strategies include evaluating only the home page, testing specific page types (login, contact, sitemap), using hierarchical depth-based selection, or the…

Page Segmentation(also: Web Page Segmentation, VIPS)

The process of dividing a web page into distinct visual or structural blocks based on layout cues such as whitespace, borders, colors, and font properties. Page segmentation algorithms like Vision Based Page Segmentation (VIPS) analyze the rendered appearance of pages to…

Page Structure Preservation(also: Layout Preservation, Structure Retention)

The principle of maintaining the original spatial layout and DOM structure of a webpage when applying accessibility enhancements, content filtering, or other modifications. Preserving page structure ensures that users' mental models of familiar websites remain intact, that…

Perceived Accessibility(also: Subjective Accessibility, Accessibility-in-Use)

Perceived accessibility refers to the subjective quality by which users experience the accessibility of a website or application, as opposed to its objective compliance with accessibility standards. Research has shown that guideline-conformant websites can still be perceived as…

Personalization Semantics(also: WAI-Adapt)

A W3C specification that defines standardized semantics enabling content to be adapted to individual user needs and preferences. Personalization Semantics allows web authors to add metadata attributes to HTML elements that describe their purpose, importance, or function in a way…

Personalized Accessibility(also: Personalized Web Accessibility, User-Tailored Accessibility)

An approach to accessibility evaluation and design that considers the specific disability profile, capabilities, and needs of individual users rather than treating accessibility as a single universal property. Personalized accessibility evaluation tools filter WCAG success…

Photophobia(also: Light Sensitivity)

A genuine physiological sensitivity to bright light, flickering light, or intense visual patterns that causes symptoms such as headaches, migraines, nausea, dizziness, and disorientation. Despite its name suggesting a psychological fear, photophobia involves real neurological…

Photosensitivity(also: Photosensitive Epilepsy, PSE)

A neurological condition in which exposure to flickering light patterns, flashing graphics, or rapid luminance changes triggers physiological responses including seizures, migraines, nausea, dizziness, and disorientation. Photosensitive epilepsy, the most dangerous form, affects…

Photosensitivity(also: Light Sensitivity, Photophobia)

An abnormal sensitivity to light that can cause discomfort, pain, or visual disturbance. Photosensitivity affects many people with visual impairments and certain neurological conditions including migraine and epilepsy. In digital accessibility, photosensitivity considerations…

Plain Language(also: Plain English, Clear Language, Simple Language)

Plain language is communication that is clear, concise, and well-organized so that the intended audience can easily find, understand, and use the information. In accessibility, plain language is essential for making content accessible to people with cognitive disabilities, low…

Plain language(also: Plain English, Easy read, Simple language)

A communication approach that uses clear, concise, and well-organised writing designed to be understood the first time it is read. Plain language avoids jargon, complex sentence structures, and ambiguous wording. It is a key accessibility practice for making information…

Platform Accessibility

The degree to which online platforms (websites, apps, social media, marketplace platforms) are usable by and inclusive of disabled people. Platform accessibility encompasses not only technical compliance with standards like WCAG but also policies, algorithms, and moderation…

Presentation Independence(also: Presentation-Independent Information)

The principle that information should be stored and served in formats that can be rendered in visual, auditory, or electronic text form without loss of meaning. Presentation-independent content has no inherent visual or auditory presentation and can be adapted to the needs of…

Print Illiteracy(also: Alipi)

A condition where a literate person is unable to meaningfully access or use written web content, not because they cannot read, but because the content is presented in a language, script, or format they do not understand. Print illiteracy distinguishes itself from traditional…

Procedural Accessibility

An aspect of web accessibility that addresses the consistency and clarity of interaction sequences and workflows within digital systems. Procedural accessibility ensures that similar services follow the same patterns of interaction — for example, all online purchasing processes…

Prosumer(also: Producer-Consumer, Prosumer Content Creator)

A person who both produces and consumes content, particularly on the web. Prosumers are not formally trained in web design or development but are responsible for creating and managing user-generated content shared online — such as blog posts, newsletters, community websites, and…

Proxy Interface(also: Accessibility Proxy, Alternative Interface)

An intermediary user interface that sits between the user and the original content, re-presenting information in a more accessible format without modifying the underlying source. In accessibility contexts, proxy interfaces are used to transform visually-encoded content (like…

Random Walk(also: Random Walk Sampling)

In web-accessibility evaluation, a random walk is a probabilistic sampling method that starts from a seed page (typically the home page) and follows outgoing links according to a probability rule — for example, with probability d follow a uniformly-chosen outgoing link, and with…