This principle focuses on making web content perceivable to all users. It means ensuring that information and user interface components can be perceived through various senses, such as sight, hearing, or touch. Providing alternatives for non-text content, using descriptive text for images, and offering captions for videos are some examples of making content perceivable.

The operability principle emphasizes that web content should be operable by all users, regardless of their abilities or the devices they use. It entails designing interfaces that can be operated with different input methods, such as a keyboard or assistive technologies. Keyboard accessibility, providing clear navigation, and avoiding elements that could cause seizures are important aspects of operability.

The understandability principle focuses on making web content understandable and comprehensible to users. It involves using clear and simple language, organizing information in a logical manner, and providing instructions or assistance when needed. By ensuring that content is easy to understand, users can effectively navigate and engage with the information provided.

The robustness principle aims to ensure that web content is compatible with a wide range of user agents (browsers, assistive technologies, etc) and remains accessible as technology evolves. It encourages using standard coding practices, adhering to HTML and CSS specifications, and avoiding reliance on specific technologies that may limit accessibility. A robust approach ensures that content can be interpreted accurately and consistently across different platforms.