Glossary
Digital accessibility glossary
The key terms around the EAA, the German BFSG, WCAG and EN 301 549 — explained concisely and clearly.
- Accessibility overlay (widget)
An accessibility overlay is a JavaScript widget that promises to adjust a website at runtime in the browser. The European Commission and expert bodies have made clear that overlays do not establish legal conformance.
Percelia is deliberately not an overlay: we deliver real findings and source-code fixes, not a runtime layer.
Related terms: Digital accessibility, Conformance statement
Read more in the guides: Overlays vs. a real audit — why widgets are legally risky
- Alternative text (alt text)
Alt text describes an image's content or function in words so screen readers can announce it (WCAG 1.1.1). Purely decorative images get an empty alt text so assistive technology skips them.
Whether alt text exists can be checked automatically — whether it is meaningful needs human or AI judgment.
Related terms: WCAG (Web Content Accessibility Guidelines), Screen reader
Read more in the guides: WCAG 2.2 AA: the checklist for your website
- Assistive technology
Assistive technology covers the tools people with disabilities use to access digital content — such as screen readers, screen magnification, voice input or specialised input devices.
Related terms: Screen reader, Digital accessibility
- BFSG (German Accessibility Strengthening Act)
The Barrierefreiheitsstärkungsgesetz (BFSG) is Germany's transposition of the European Accessibility Act. It requires many providers of digital products and services to make them accessible and applies since 28 June 2025.
Affected are online shops, banking, transport and other B2C services; the technical benchmark is WCAG / EN 301 549.
Related terms: European Accessibility Act (EAA), EN 301 549, WCAG (Web Content Accessibility Guidelines)
Read more in the guides: BFSG: Who is affected?, EAA and EN 301 549 explained
- Conformance levels (A, AA, AAA)
The WCAG define three conformance levels: A (minimum), AA (the standard for legal conformance) and AAA (highest). Each success criterion is assigned to exactly one level.
In practice AA is the target — AAA is not fully achievable for all content.
Related terms: WCAG (Web Content Accessibility Guidelines), Success criterion
Read more in the guides: WCAG 2.2 AA: the checklist for your website
- Conformance statement
A conformance statement documents, in a traceable way, how accessible a product is against WCAG / EN 301 549. It is a self-declaration based on methodology and evidence — not an official certification.
Related terms: VPAT (Voluntary Product Accessibility Template), EN 301 549
- Contrast ratio
The contrast ratio measures the luminance difference between text and its background. WCAG AA requires at least 4.5:1 for normal text and 3:1 for large text (WCAG 1.4.3).
Related terms: WCAG (Web Content Accessibility Guidelines), Success criterion
Read more in the guides: WCAG 2.2 AA: the checklist for your website
- Digital accessibility
Digital accessibility means websites, apps and digital documents are built so that people with disabilities can perceive, operate and understand them — including with assistive technology such as screen readers.
The benchmark is recognised standards, above all the WCAG and the European standard EN 301 549.
Related terms: WCAG (Web Content Accessibility Guidelines), BFSG (German Accessibility Strengthening Act), Assistive technology
Read more in the guides: BFSG: Who is affected?
- EN 301 549
EN 301 549 is the European standard for the accessibility of ICT products and services. For the web it adopts the WCAG success criteria and adds further requirements (e.g. for hardware and documents).
It is the harmonised technical benchmark the EAA and BFSG rely on.
Related terms: WCAG (Web Content Accessibility Guidelines), European Accessibility Act (EAA), VPAT (Voluntary Product Accessibility Template)
Read more in the guides: EAA and EN 301 549 explained
- European Accessibility Act (EAA)
The European Accessibility Act (EAA) is an EU directive setting uniform accessibility requirements for many digital products and services. Each member state transposes it into national law — in Germany via the BFSG.
Related terms: BFSG (German Accessibility Strengthening Act), EN 301 549
Read more in the guides: EAA and EN 301 549 explained
- Focus indicator
The focus indicator is the visible marker showing which element currently has keyboard focus (e.g. an outline around a button). It must be clearly visible (WCAG 2.4.7, extended in WCAG 2.2 by 2.4.11 on its appearance).
Related terms: Keyboard accessibility, WCAG (Web Content Accessibility Guidelines)
Read more in the guides: WCAG 2.2 AA: the checklist for your website
- Keyboard accessibility
Keyboard accessibility means every function of a page can be used with the keyboard alone — without a mouse (WCAG 2.1.1). Focus must never get stuck (no “keyboard trap”, WCAG 2.1.2).
Many people with motor impairments and screen-reader users rely entirely on the keyboard.
Related terms: Focus indicator, Screen reader
Read more in the guides: Accessible checkout: 7 common mistakes
- Landmark
Landmarks are regions of a page with a clear role — such as navigation, main content or footer — marked up with HTML elements like <nav>, <main> and <footer>. Screen-reader users jump through the page by them.
Related terms: Semantic HTML, Screen reader
- POUR principles
POUR captures the four foundational principles of the WCAG: perceivable, operable, understandable and robust. Every success criterion belongs to one of these principles.
Related terms: WCAG (Web Content Accessibility Guidelines), Success criterion
- Screen reader
A screen reader is software that outputs screen content as speech or braille. It relies on a page's semantic structure — headings, landmarks, labels and alternative text.
Common screen readers are NVDA and JAWS (Windows), VoiceOver (Apple) and TalkBack (Android).
Related terms: Alternative text (alt text), WAI-ARIA, Assistive technology
- Semantic HTML
Semantic HTML means using the right element for each purpose — <button> for buttons, <a> for links, headings in correct order. This lets browsers and assistive technology understand the page without extra work.
It is the foundation of all accessibility and often makes additional ARIA unnecessary.
- Success criterion
A success criterion is a single, testable WCAG requirement — for example 1.4.3 (contrast) or 2.4.7 (focus visible). Conformance is assessed per success criterion.
Related terms: WCAG (Web Content Accessibility Guidelines), Conformance levels (A, AA, AAA)
- VPAT (Voluntary Product Accessibility Template)
A VPAT is a standardised document recording, for each criterion, the degree to which a product meets it (supports / partially supports / does not support). It is the common format for an accessibility conformance statement.
Percelia derives such a statement from the findings — signed off only once nothing remains in review.
Related terms: Conformance statement, EN 301 549
Read more in the guides: EAA and EN 301 549 explained
- WAI-ARIA
WAI-ARIA is a set of HTML attributes that give assistive technology extra information about the roles, states and properties of controls — mainly where native HTML falls short.
Rule of thumb: semantic HTML first, ARIA only to supplement. Misused ARIA does more harm than good.
Related terms: Semantic HTML, Screen reader, Landmark
- WCAG (Web Content Accessibility Guidelines)
The WCAG are the W3C's international standard for accessible web content. They are organised into the four POUR principles and individual, testable success criteria; the current versions are WCAG 2.1 and 2.2.
For legal conformance in the EU, level AA is usually the relevant bar.
Related terms: Conformance levels (A, AA, AAA), POUR principles, Success criterion, EN 301 549
Read more in the guides: WCAG 2.2 AA: the checklist for your website
Request a free scan
Tell us your domain — we run a free initial scan and show you the most important barriers.