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Glossary

Accessibility & HTML Glossary

Clear, example-led definitions of the accessibility and HTML terms that show up in Rocket Validator reports.

  • Accessibility

    ARIA

    ARIA (Accessible Rich Internet Applications) is a set of HTML attributes that add accessibility semantics such as roles, states, and properties to custom UI components.
  • Accessibility

    ARIA Hidden and Inert Content

    ARIA hidden and inert content refers to techniques that remove elements from the accessibility tree or disable their interactivity, preventing screen readers and keyboard users from encountering decorative, redundant, or temporarily irrelevant content such as background page content behind a modal dialog.
  • Accessibility

    ARIA Labeling Techniques

    ARIA labeling techniques are a set of methods using WAI-ARIA attributes—primarily aria-label, aria-labelledby, and aria-describedby—to provide accessible names and descriptions to interactive elements, regions, and widgets so that assistive technologies can convey their purpose to users.
  • Accessibility

    ARIA Live Politeness Settings

    ARIA live politeness settings control how assistive technologies announce dynamic content changes, using the aria-live attribute with values of off, polite, or assertive to determine whether updates interrupt the user immediately, wait for a pause, or remain silent.
  • Accessibility

    ARIA Widget Patterns

    ARIA widget patterns are standardized interaction models defined by the WAI-ARIA Authoring Practices that describe the expected keyboard behavior, focus management, and ARIA roles, states, and properties for custom interactive UI components like tabs, menus, dialogs, and tree views.
  • Accessibility

    Accessibility Audit

    An accessibility audit is a structured evaluation of a website or app against accessibility standards, combining automated checks with manual and assistive-technology testing.
  • Accessibility

    Accessibility Tree

    The accessibility tree is a parallel structure to the DOM tree that browsers construct to represent the semantic meaning of a web page for assistive technologies such as screen readers, braille displays, and voice control software.
  • Accessibility

    Accessible Description

    An accessible description is a supplementary text string, computed by the browser's accessibility API, that provides additional context or instructions about a user interface element beyond what its accessible name conveys.
  • Accessibility

    Accessible Name

    An accessible name is the text assistive technologies use to identify a UI element, derived from sources such as visible text, labels, alt text, or ARIA naming attributes.
  • Accessibility

    Accessible Name Computation

    Accessible Name Computation is the algorithm defined by the W3C that browsers and assistive technologies use to determine the text name of an interactive element, resolving multiple possible sources—such as aria-labelledby, aria-label, HTML <label>, and element content—into a single accessible name string.
  • Accessibility

    Alt Text

    Alt text (alternative text) is a short written description added to an image's HTML code that conveys the image's content and function to users who cannot see it, primarily through screen readers.
  • Accessibility

    Browser Accessibility API Mapping

    Browser Accessibility API Mapping is the process by which web browsers translate HTML elements, attributes, and ARIA annotations into structured data exposed through platform-specific accessibility APIs, enabling assistive technologies like screen readers to understand and interact with web content.
  • Accessibility

    Color Contrast

    Color contrast is the luminance difference between foreground and background colors, measured as a ratio, used to determine whether text and UI components are readable for users with low vision.
  • Accessibility

    Content Reflow and Responsive Zoom

    Content reflow and responsive zoom refers to the ability of web content to adapt its layout when users zoom in up to 400% or resize their viewport, ensuring all information and functionality remains available without requiring horizontal scrolling in two dimensions.
  • HTML

    Document Language Declaration

    A document language declaration specifies the primary human language of a web page by setting the lang attribute on the <html> element, enabling browsers, screen readers, and other tools to process and present the content correctly.
  • Accessibility

    Error Identification and Suggestion

    Error identification and suggestion is an accessibility practice requiring that input errors are automatically detected, clearly described to the user in text, and accompanied by actionable suggestions for correction when possible.
  • Accessibility

    Focus Indicator

    A focus indicator is a visible outline or style change that shows which interactive element on a web page currently has keyboard focus, enabling users who navigate without a mouse to track their position on the screen.
  • Accessibility

    Focus Trap

    A focus trap is a technique that constrains keyboard focus within a specific region of a page—such as a modal dialog—so that pressing Tab or Shift+Tab cycles only through the interactive elements inside that region until the user explicitly dismisses it.
  • Accessibility

    Form Label Association

    Form label association is the programmatic connection between a form control (such as an input, select, or textarea) and its descriptive label, enabling assistive technologies to announce the purpose of the control when it receives focus.
  • HTML

    HTML Validation

    HTML validation is the process of checking markup against standards to detect structural and syntax errors that can break rendering, accessibility, and interoperability.
  • Accessibility

    Heading Hierarchy

    Heading hierarchy is the structured ordering of HTML heading elements (<h1> through <h6>) in a logical, nested sequence that reflects the document's content outline, enabling users—especially those relying on assistive technologies—to understand and navigate a page's organization.
  • Accessibility

    Input Purpose and Autocomplete

    Input purpose and autocomplete refer to the practice of programmatically identifying the purpose of form fields using the HTML autocomplete attribute, enabling browsers and assistive technologies to automatically fill in user data and present fields in ways that are easier to understand and complete.
  • Accessibility

    Keyboard Accessibility

    Keyboard accessibility means every interactive part of a website can be reached and operated using a keyboard alone, with logical focus order and visible focus indication.
  • Accessibility

    Landmark Roles

    Landmark roles are specific ARIA roles or HTML5 semantic elements that define the major structural regions of a web page, enabling assistive technology users to quickly identify and navigate to key sections such as the banner, navigation, main content, and footer.
  • Accessibility

    Live Region

    A live region is an area of a web page that dynamically updates its content and communicates those changes to assistive technologies like screen readers, without requiring the user to navigate to the updated area.
  • Accessibility

    Reduced Motion Preference

    The reduced motion preference is an operating system–level setting that users can enable to minimize or eliminate animations, transitions, and other non-essential motion on screen. Web developers can detect this preference using the prefers-reduced-motion CSS media query and adjust or disable animations accordingly.
  • Accessibility

    Role, State, and Property

    In WAI-ARIA, roles, states, and properties are the three categories of attributes that define what a UI element is, what condition it is in, and what characteristics it has, enabling assistive technologies to present and interact with web content accurately.
  • Accessibility

    Screen Reader

    A screen reader is assistive software that converts on-screen content into speech or braille output, allowing blind and low-vision users to navigate websites through structure and semantics.
  • HTML

    Semantic HTML

    Semantic HTML uses elements that describe meaning and structure, such as <main>, <nav>, and <button>, so browsers and assistive technologies can correctly interpret page content.
  • Accessibility

    Tab Order

    Tab order is the sequence in which interactive elements on a web page receive keyboard focus as a user presses the Tab key, determined by the document's source order and any explicit tabindex attributes.
  • Accessibility

    Text Alternatives

    Text alternatives are textual substitutes for non-text content such as images, icons, videos, and controls, enabling people who cannot perceive the original content to understand its meaning and purpose through assistive technologies like screen readers.
  • Accessibility

    WCAG

    WCAG (Web Content Accessibility Guidelines) is the global technical standard for making web content accessible to people with disabilities, published by the W3C Web Accessibility Initiative.
  • Accessibility

    WCAG Conformance Levels

    WCAG Conformance Levels are the three tiers of accessibility compliance—Level A, Level AA, and Level AAA—defined by the Web Content Accessibility Guidelines to classify success criteria by their impact and priority for making web content accessible to people with disabilities.
  • Accessibility

    WCAG Success Criteria

    WCAG Success Criteria are the individual, testable requirements defined by the Web Content Accessibility Guidelines that determine whether web content is accessible to people with disabilities. Each criterion addresses a specific accessibility barrier and is assigned a conformance level of A, AA, or AAA.
  • HTML

    tabindex Attribute

    The tabindex attribute is an HTML attribute that controls whether an element is focusable via keyboard navigation, and optionally determines its position in the sequential tab order of the page.
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