POUR - Accessibility Principles
Perceivable
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.
Operable
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.
Understandable
Information and the operation of user interface must be understandable.
The Understandable principle includes guidelines for readable content, predictable content, and input assistance.
Robust
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.