Definition

POUR (perceivable, operable, understandable, robust)

The four founding principles of WCAG. All accessible content must be perceivable, operable, understandable and robust.

WCAG rest on four principles, summarised as POUR. Perceivable: information must be able to be perceived (for example a text alternative for images). Operable: the interface must be usable (for example with the keyboard).

Understandable: content and operation must be clear (for example explicit error messages). Robust: content must remain interpretable by browsers and assistive technologies.