What is meant by the robustness principle in web accessibility?

The robustness principle in web accessibility refers to the necessity for content to be compatible with a wide variety of user agents, which includes browsers and assistive technologies. This means that the way content is coded and structured should allow it to function correctly across different platforms, devices, and user scenarios. It emphasizes the importance of ensuring that content is accessible not just for typical users but also for those relying on assistive technologies such as screen readers, alternative input devices, or mobile devices with varying capabilities.

By adhering to this principle, web content can ensure a more inclusive experience for all users, allowing individuals with disabilities to access information and functionality without barriers. In contrast, insisting that content be visually appealing is more concerned with aesthetics rather than functionality. Similarly, while adapting content for different devices is important for usability, it does not directly address the broader compatibility with user agents or assistive technologies. Limiting content to specific browsers contravenes the notion of robustness, as it creates potential accessibility barriers for users who do not use those specific browsers or technologies.