Three Flashes
Web pages do not contain anything that flashes more than three times in any one second period.
In plain language
This is the strictest flashing rule: nothing on a page can flash more than three times per second — no exceptions for small areas or dim flashes like the AA-level version allows.
Why it matters
Even small or dim flashing content can trigger seizures in some people with photosensitive epilepsy. This stricter rule removes the size and brightness exceptions entirely, making the site safer for the most sensitive users.
In practice
Fails this criterion
A warning icon on the page blinks on and off 4 times within one second.
Meets this criterion
The same icon is edited so it flashes no more than 3 times in any one-second period, regardless of its size or brightness.
Test it yourself
Watch any blinking, flashing, or strobing content on the site closely, even small icons. If anything flashes more than 3 times per second, this criterion is failing — no exceptions.