The Web Content Accessibility Guidelines (WCAG) are the most widely-used and most trusted digital accessibility standards. WCAG is constructed by groupings of related success criteria that form guidelines. Guidelines are themselves organized by four key accessibility principles: Perceivable, Operable, Understandable, and Robust. The acronym POUR is sometimes used to describe accessible content that meets the requirements of those principles.
WCAG 2.1 is the latest version formally recommended by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C).
Information and user interface components must be presentable to users in ways they can perceive.
The Perceivable principle includes guidelines for text alternatives, time-based media, adaptable content, and distinguishable content.
User interface components and navigation must be operable.
The Operable principle includes guidelines for keyboard accessibility, providing enough time, avoiding seizures and physical reactions, navigation, and input modalities.
Information and the operation of user interface must be understandable.
The Understandable principle includes guidelines for readable content, predictable content, and input assistance.
Content must be robust enough that it can be interpreted by a wide variety of user agents, including assistive technologies.
The Robust principle includes guidelines for content that is compatible with current and future user agents.