Textbook of Usability

Also known as: A11y

Accessibility refers to the design of products, devices, services, and environments so that they can be used by people with disabilities. In digital contexts, it means ensuring that web sites, applications, and software can be used by people with visual, auditory, motor, or cognitive impairments — including those who rely on assistive technologies like screen readers, voice control, and switch devices.

Accessibility is often called "A11y" (11 letters between A and y). It is commonly misunderstood as a niche concern or an add-on for a small group. In reality:

• 15% of the world's population has some form of disability (WHO estimate)
• Temporary and situational disabilities affect everyone at times (broken arm, bright sunlight on a phone screen, juggling a child)
• Ageing gradually introduces vision, hearing, and motor limitations for all long-lived users
• Accessibility improvements typically benefit all users (captions help in noisy environments; high contrast helps in sunlight)

Digital accessibility standards are codified in WCAG (Web Content Accessibility Guidelines) and legally enforced in many jurisdictions through laws like the ADA, Equality Act, and European Accessibility Act.

Common accessibility practices:

• Alt text for images
• Semantic HTML for screen reader navigation
• Keyboard accessibility for all interactive elements
• Sufficient colour contrast for low-vision users
• Captions and transcripts for audio/video
• Clear language for cognitive accessibility
• Redundant encoding so information isn't lost if one channel is unavailable

Accessibility is not optional — it is fundamental to usability.