Guideline 3:
Allow configuration not to render some content that may reduce accessibility

Ensure that the user may turn off rendering of content (e.g., audio, video, scripts) that may reduce accessibility by obscuring other content or disorienting the user.

Some content or behavior specified by the author may make the user agent unusable or may obscure information. For instance, flashing content may trigger seizures in people with photosensitive epilepsy, or may make a Web page too distracting to be usable by someone with a cognitive disability. Blinking text can affect screen reader users, since screen readers (in conjunction with speech synthesizers or braille displays) may re-render the text every time it blinks. Distracting background images, colors, or sounds may make it impossible for users to see or hear other content. Dynamically changing Web content may cause problems for some assistive technologies. Scripts that cause unanticipated changes (e.g., viewports that open without notice or automatic content retrieval) may disorient some users with cognitive disabilities.

This guideline requires the user agent to allow configuration so that, when loading Web resources, the user agent does not render content in a manner that might pose accessibility problems. Requirements for interactive control of rendered content are part of guideline 4.