Which of the following is a requirement for EPUB accessibility?

The requirement for EPUB accessibility is that it must be discoverable, accessible, and optimized. This means that an EPUB document should be structured in a way that allows users, including those with disabilities, to easily discover and navigate its content. Accessibility refers to the document being usable by all people, including those with visual, auditory, or cognitive impairments. Optimization involves ensuring that the content is presented in a way that is compatible with various devices and assistive technologies, enhancing usability.

The other choices, while they may be relevant in certain contexts, do not fundamentally address the core requirements of EPUB accessibility. For instance, while compatible audio formats can enhance accessibility, they are not a strict requirement for all EPUB documents. Similarly, shared editing capabilities might improve collaboration during document creation, but they do not impact the accessibility of the content itself. Lastly, the notion that no images can be used contradicts the principles of accessibility, as images can be made accessible through alternative text descriptions and careful formatting. Thus, the emphasis on being discoverable, accessible, and optimized is what truly encapsulates the necessary criteria for ensuring EPUB documents are usable by everyone.