The international standard for digital accessibility, WCAG, is organized into four major principles:
- Perceivable
- Operable
- Understandable
- Robust
These principles spell the acronym POUR. They describe a flexible approach to accessible design that is relevant across digital contexts.
In WCAG, each principle introduces a section with a list of requirements, or rules, that describe how to achieve digital accessibility.
Explanations of the principles below are adapted from a plain language Accessibility Guidelines Summary.
Perceivable: Easy to Perceive
Present information in ways that people can recognize and use, no matter what senses they rely on or how they consume content. For example, some people have low vision, have hearing loss, or use assistive technologies like screen readers.
Perceivable means accessible across differences in human senses, and includes requirements for:
- Captions for audio/video
- Text description for images
- Enough contrast
Operable: Easy to Operate
Make controls and information easy to navigate and use, no matter how someone interacts with it. For example people who do not use a mouse may use their voice, or press the 'Tab' key to move the keyboard's focus to interactive controls.
Operable means accessible across differences in technologies, and includes requirements for:
- Usability with keyboard only, mobile, voice input, other assistive technologies
- Meaningful link text
- Meaningful labels and page titles
Understandable: Easy to Understand
Make it easy for people to understand information and how to complete tasks.
Understandable means accessible across differences in cognitive needs, and includes requirements for:
- Predictable and consistent design
- Understandable language
- Tolerance for error
Robust: Compatible Across Devices
Make content and applications that work with different web browsers, assistive technologies, operating systems, and versions.
Robust means accessible across differences in software and devices, and includes requirements for:
- Universal formats
- Valid code