Which of the following is a new Success Criterion in WCAG 2.1?

The correct answer focuses on a new Success Criterion introduced in WCAG 2.1, specifically related to orientation. Success Criterion 1.3.4, titled "Orientation," addresses the need for content to be accessible regardless of the user's orientation or device rotation, which is particularly significant for mobile devices. This criterion ensures that content remains usable in both portrait and landscape orientations, promoting a more accessible experience for users with disabilities who may rely on specific device orientations for usability.

In contrast, the other listed Success Criteria are part of WCAG 2.0 and were not newly introduced in WCAG 2.1. For example, Audio Description (1.2.1) focuses on providing aural descriptions for video content, Link Purpose (2.4.4) emphasizes clear link descriptions, and Language of Page (3.1.1) ensures the primary language of a page is identified. These criteria already existed in the previous versions of WCAG and were not additions in the 2.1 update. Understanding these distinctions highlights the evolving nature of web accessibility standards and the emphasis on making digital content usable across diverse contexts and devices.