The intent of this Success Criterion is to make users aware of important changes in content that are not given focus, and to do so in a way that doesn't unnecessarily interrupt their work.

The intended beneficiaries are blind and low vision users of assistive technologies with screen reader capabilities. An additional benefit is that assistive technologies for users with cognitive disabilities may achieve an alternative means of indicating (or even delaying or supressing) status messages, as preferred by the user.

The scope of this Success Criterion is specific to changes in content that involve status messages. A status message is a defined term in WCAG. There are two main criteria that determine whether something meets the definition of a status message:

https://www.w3.org/WAI/WCAG21/Understanding/status-messages.html