Q1 of 24 · Accessibility
What are the four POUR principles of WCAG and what does each mean for testing?
Short answer
Short answer: POUR stands for Perceivable, Operable, Understandable, and Robust. Each addresses a different failure mode: content that can't be seen or heard, interfaces that can't be controlled, content that can't be understood, and content that breaks with assistive technology.
Detail
Perceivable: information and UI components must be presentable to users in ways they can perceive — nothing can be invisible to all senses. Test implications: images need alt text, videos need captions, audio-only content needs transcripts, and content can't be conveyed by colour alone.
Operable: UI components and navigation must be operable by all users. Test implications: every feature must be reachable and usable via keyboard alone, there must be no timing traps (or timing can be extended), and flashing content must stay below the seizure threshold.
Understandable: information and UI operation must be understandable. Test implications: the page language is declared, form errors are clearly labelled and identify the specific field, instructions are available before errors occur, and navigation is consistent across pages.
Robust: content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies. Test implications: HTML is valid and well-structured, ARIA is used correctly (not speculatively), and the page works with the assistive technology combinations your users actually use — not just theoretically.
A useful framing for the interview: POUR describes who is excluded by a failure. A missing alt text fails Perceivable and excludes blind users. A keyboard trap fails Operable and excludes motor-impaired users who rely on keyboard navigation.