2.2 Avoid causing content to blink
WAI checkpoint 7.2
Full WAI text: "Until user agents allow users to control blinking, avoid causing content to blink (i.e., change presentation at a regular rate, such as turning on and off)."
User agents are software which people use to access Web content. These include graphical browsers, text-only browsers, voice browsers, mobile phones, multimedia players, plug-ins and assistive technologies such as screen readers, screen magnifiers and voice recognition software.
It is possible to cause content to blink or flash by inserting commands to do this into the web page. This is usually done to create a novel effect, but should be avoided at present, since not all user agents allow the user to control the rate of blinking or to disable it.
Flickering may induce epileptic seizures in users if it occurs regularly at a particular rate.
It is also difficult to read content which is flashing on and off or to read content when something else on the page is flashing. Blinking is particularly distracting for users who have limited reading ability or difficulty concentrating because of noise, stress or a learning disorder.
Directions and Techniques
Ensure that screen flicker is within a safe range
Keep blinking to less than 2 flashes per second (Hertz) and do not change quickly from from dark to light.
Provide a mechanism or control for controlling or disabling blinking
If you create blinking effects using Java applets or other techniques, you should provide an obvious control which allows the user to freeze movement or disable the flicker effect.
How you could check for this:
There are no specific test methods recommended for this guideline.