Imagine, for a moment, that you're on a beautiful desert island. You're sitting in a beach chair, watching the waves come in, and contemplating WCAG compliance. Just as you're on the brink of a major breakthrough with regard to website accessibility, a roving pack of insurance salesmen start throwing sand at you and telling you that, in all likelihood, your woefully unprotected home is currently on fire.
It's impossible to concentrate with interruptions, and some interruptive web features, like updates or alert messages, may pose particular difficulty for some users.
Those experiencing cognitive limitations or attention deficit disorders need to be able to focus on content without disruption. In addition, anyone using a screen reader would have trouble interacting with the content on your website if it suddenly underwent an update or was obscured by some alert.
This guideline asks that you allow those using your site to postpone or turn off any updates or alert messages. This applies to interruptive features that originate either from you, the content
This rule doesn't apply to alerts that convey crucial information related to health and safety, such as civil emergency alert messages, or loss or damage to property (this includes data and connectivity loss). In such cases, the dire nature of the message outweighs any accessibility concerns.