Avoid causing the screen to flicker.
Flickering/flashing Web page elements can cause seizures in users with photosensitive epilepsy.
Avoid Java applets/ActiveX objects and JavaScript/other scripting languages that cause the screen to flicker or otherwise strobe light effect.
Note: BLINK and MARQUEE tags should not be used.
View WAI checkpoint 7.1 - Until user agents allow users to control flickering, avoid causing the screen to flicker.