Four Principles of Accessibility

A human head, symbolizing perception.

Perception

Information and user interface components must be presentable to users in ways they can perceive.

A car, symbolizing operable user interfaces.

Operable

User interface components and navigation must be operable by all users.

A brain-shaped cloud, symbolizing understandability.

Understandable

Information and the operation of the user interface must be understandable.

A keyboard, symbolizing robustness.

Robust

Content must be robust enough to be interpreted reliably by a wide variety of user agents, including assistive technologies.