This test is a "catch-all" requirement for any content that is not readable and/or interactable using assistive technology. Assistive technology includes but is not limited to screen readers, text readers, speech recognition/input, and keyboard input.
If you are using assistive technology, and come across any content that can't be interacted with that does not fall into any other more specific guideline, mark it under this criterion.
Examples may include
A CAPTCHA where no modality provided is usable by a specific assistive technology.
aria-hidden="true" is used on text that a sighted user currently has the ability to read. (e.g., a collapsed accordion should have contents hidden, an expanded accordion should not have contents hidden).
Screen reader only text is incorrectly hidden with CSS (e.g., using display: none; or visibility: hidden; instead of using clip)
