Perceivable
Users must be able to get information using at least one of their senses. Content that is only in one form, just images or just sound, cannot be seen or heard by some users.
Key point
Perceivable means the user can receive the content, not just that the content is there. A video with audio description can be understood by blind users; the same video without it cannot.
Text alternatives
Any content that is not text must have a text alternative that has the same purpose.
Example
A photo of a product on a shopping website needs alt text that explains what the picture shows, not just a file name like “img0042.jpg,” so people using screen readers get the same information as people who can see.
Time-based media
Audio and video need other options so people who cannot hear or see them can get the same information.
Example
A recorded lecture needs captions for deaf users and an audio description for blind users who cannot see what is happening on the screen.
Adaptable
The meaning must stay the same even when the way it is shown changes.
Example
A table that looks neat on the screen can sound like a mix of random words when a screen reader reads it aloud. That happens because the code does not reflect the way it looks.
Key point
“Presentation” is not just about what you see. It includes any way content is shown, like audio, braille, and adjusting to small screens.
Distinguishable
Content should be easy to see apart from the background and other items around it. This can be done by using tools like colour contrast and allowing text to be resized.
Example
Light grey text on a white background may look neat to a designer, but it is hard for people with low vision or colour blindness to see the words clearly.
Key point
Colour should never be the only way to show information. For example, using just red and green to show pass and fail can be confusing for people who cannot see red and green clearly.