A popup warning on a website stating, "Your session is about to expire. Would you like to continue?" is an example of which web accessibility principle?

The correct answer is that the popup warning exemplifies the web accessibility principle of being understandable. This principle emphasizes that information and the operation of user interface must be clear and easily comprehensible to users.

In this case, the popup clearly communicates a specific action that the user needs to consider regarding their session status. It informs them that their session is about to expire and prompts them to take action by asking if they would like to continue. This clear messaging ensures that users, regardless of their experience level or necessities, can understand the situation and respond appropriately.

While the other principles—perceivable, operable, and robust—play significant roles in web accessibility, they relate to different aspects. Perceivable focuses on providing information in ways that can be sensed by users (e.g., text that can be read aloud, visual content that can be distinguished). Operable relates to ensuring that all users can navigate and interact with the interface effectively. Robust involves creating content that can be reliably interpreted by a variety of user agents, including assistive technologies. Each of these principles contributes to an accessible web environment, but the clarity and comprehension of the message in the popup specifically align with the principle of being understandable.