Guideline 7. Ensure user control of time-sensitive content changes
Source Article: http://www.w3.org/TR/WCAG10/#gl-movement
Have you ever watched a foreign film or the news on mute and tried to keep up with the subtitles. It can be a stressful task. There are also so many marquees that have racing text. The subtitles might leave you lost but at least you can keep watching the marquees and pick up a couple of words each time. Talk about a headache. This is a prime example of what a web site should not be, yet many do. I believe this follows under the category of just because you can, doesn't mean you should.
There are currently no user agents that allow users to control moveable or time-sensitive features. This makes it annoying for the average user but it can also be physically dangerous to people with certain physical disabilities.
In fact, people with photosensitive epilepsy can have seizures triggered by flickering or flashing. So, the first priority here would be to avoid causing the screen to flicker or blink. If a blink effect is needed, use a slow regular change such as an on/off effect.
There are many marquees that nobody can keep up with but there are many others that those with cognitive disabilities that have a hard time keeping up with almost anything that's moving. If moving content must be included, it needs to have controls so the user can freeze the content. This can be provided within the applet or script but can also be done in CSS where it is easy to turn off.
Pages should not be encoded with auto refresh. If there is content that needs refreshing, it should be coded using some other method. For instance, java script can often be used to refresh certain elements. If an auto redirect is necessary, it should be configured through the server, not the regular markup.
As always, make sure everything has a clear text equivalent.
It's amazing to me how many different handicaps are effected by web design. Sometimes they might just be an easy excuse for making something accessible. I will do my best not to annoy my average user and send my handicapped user into a seizure by using time-sensitive content changes sparingly and by providing controls to shut them off.
