Which of the following is NOT a feature of HTML5 APIs?

The choice referring to enhancing the security of mobile devices is not a feature of HTML5 APIs. HTML5 primarily focuses on providing features that enhance the capabilities of web applications and improve user experience directly through the web browser.

The HTML5 APIs are designed to facilitate the creation of multimedia applications, such as those employing audio and video elements seamlessly within web pages. They also support real-time data communication through technologies like WebSockets, allowing applications to transmit data in real time without needing to refresh the page.

Improving web browser compatibility is an overarching goal of HTML5, helping to standardize web application features across different browsers, thus enhancing the uniformity of web experiences.

By contrast, security enhancements for mobile devices go beyond the scope of HTML5 itself. HTML5 does not directly address the security vulnerabilities of mobile operating systems or devices. Security measures generally require a broader approach involving both software and hardware strategies not encapsulated by the HTML5 API features.