What is an example of an operable principle in web accessibility?

The principle of operability in web accessibility focuses on ensuring that all users can navigate and interact with web content effectively, regardless of their abilities or the devices they use. Ensuring that all functionality is available from a keyboard is a key aspect of this principle. This is particularly important for users who cannot use a mouse due to mobility impairments or other disabilities. By enabling keyboard navigation for all interactive elements on a website, you provide essential access to functionalities like forms, menus, and buttons, ensuring that all users can perform necessary tasks.

In contrast, providing text alternatives for non-text content pertains to the perceivable principle, which ensures that all users can understand the content being presented. Making content easier to read and understand falls under the understandable principle, aimed at ensuring that information is presented in a clear manner. Creating robust content that can be interpreted by various user agents aligns with the robust principle, which focuses on compatibility with various technologies and assistive devices. Thus, the emphasis on keyboard accessibility distinctly categorizes it under operability, illustrating why this is the correct choice in the context of web accessibility principles.