A11y (Accessibility)

Rédigé par David Brulin, co-fondateur de Quai des Balises

A11y (Accessibility) is the numeronym for "accessibility" — the 11 stands for the letters between A and y. It refers to designing and building digital products that people with disabilities can perceive, operate and understand, regardless of visual, auditory, motor or cognitive limitations.

The four POUR principles behind A11y

Digital accessibility is structured around the four principles defined by the Web Content Accessibility Guidelines (WCAG), summarised by the acronym POUR. Every accessible interface must satisfy all four.

Perceivable: information and interface elements must be presentable in ways users can perceive — text alternatives for images, captions for video, sufficient colour contrast.
Operable: all functionality must work via keyboard, with enough time to interact and no content that triggers seizures.
Understandable: content and operation must be readable and predictable, with clear error identification and guidance.
Robust: content must be reliably interpreted by a wide range of user agents, including assistive technologies like screen readers.

In practice, A11y relies on semantic HTML, correct heading structure, descriptive alternative text, accessible names for interactive elements, visible focus states, and ARIA attributes used only where native HTML is insufficient.

WCAG conformance levels and what they cover

WCAG, published by the W3C, is the international reference standard for digital accessibility. It defines three conformance levels, each adding success criteria on top of the previous one. Level AA is the threshold most legal frameworks and procurement requirements target.

Level	Scope	Typical use
A	Minimum criteria — removes the most severe barriers (keyboard access, text alternatives, no keyboard traps)	Baseline; rarely sufficient on its own
AA	Adds contrast ratios, resizable text, consistent navigation, error suggestions	The de facto target for public and B2B websites
AAA	Strictest criteria — sign language for audio, extended contrast, context-sensitive help	Specialised content; not expected site-wide

A11y also intersects with standards such as the EN 301 549 specification used across Europe, which references WCAG as its technical core.

Business benefits beyond compliance

Accessibility is often framed as a legal obligation, but the engineering and commercial returns extend well beyond avoiding risk.

Wider reach: accessible products serve users with permanent, temporary or situational impairments — a broader audience than disability statistics alone suggest.
SEO overlap: semantic markup, descriptive alt text and clear heading hierarchies help both assistive technologies and search engine crawlers.
Better usability for everyone: keyboard support, readable contrast and clear error messages improve the experience for all users, not only those with disabilities.
Lower remediation cost: building A11y into design and development from the start is far cheaper than retrofitting it after an audit.
Procurement eligibility: many public-sector and enterprise tenders require documented WCAG conformance.

Questions fréquentes

A11y is a numeronym: the number 11 replaces the eleven letters between the first "A" and the final "y" in the word "accessibility". This shorthand is common in technical communities, mirroring similar abbreviations such as i18n for internationalization and l10n for localization. It is pronounced either as the individual characters or as "ally".

A11y is the general concept of making digital products usable by people with disabilities. WCAG (Web Content Accessibility Guidelines) is the concrete W3C standard that defines measurable success criteria for achieving accessibility. In short, A11y is the goal and WCAG is the framework used to specify, test and certify how well that goal is met.

Level AA is the conformance level most organisations should aim for. It covers the criteria addressed by major accessibility regulations and public procurement requirements, including colour contrast, resizable text and consistent navigation. Level A alone leaves significant barriers, while Level AAA is typically reserved for specialised content rather than entire sites.

Yes. Many accessibility practices directly support search engine optimisation: semantic HTML, logical heading hierarchies, descriptive alternative text for images and meaningful link labels are read by both assistive technologies and search crawlers. Building accessible markup therefore improves how machines and users alike interpret your content, without duplicating effort.

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