Understanding Accessibility
by Vivienne Trulock
Guideline 7. Ensure user control of time-sensitive content changes.
Do not have animated elements if avoidable. Where it is not avoidable, the user must be able to turn them off. There are 5 specific checkpoints in Guideline 7.
| No. | Checkpoint | Priority | How to check | Disability Accommodated |
|---|---|---|---|---|
| 7.1 | Until user agents allow users to control flickering, avoid causing the screen to flicker | .Priority 1 | .Manual check for 7.1 | Epileptic ADD |
| 7.2 | 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) | .Priority 2 | . Manual check for 7.2 | Epileptic ADD |
| 7.3 | Until user agents allow users to freeze moving content, avoid movement in pages | .Priority 2 | .WebXact Automatic check | Epileptic |
| 7.4 | Until user agents provide the ability to stop the refresh, do not create periodically auto-refreshing pages | .Priority 2 | . WebXact Automatic check | Blind |
| 7.5 | Until user agents provide the ability to stop auto-redirect, do not use markup to redirect pages automatically. Instead, configure the server to perform redirects | .Priority 2 | Blind |
Checkpoint 7.1 - Until user agents allow users to control flickering, avoid causing the screen to flicker
Individuals suffering from epilepsy may suffer an attack if the screen flickers or mimics strobe light effects where the flicker rate is between 4 and 59 flashes per second. The peak rate occurs at 20 flashes per second.
How do I do it?
The easiest way to avoid this checkpoint is to not use animated gifs. If you are making your own animated gifs, set the delay time so that the flicker rate is outside the range of 4 to 59 flashes per second or Hertz (Hz). Hz = Delay Time in hundredths of a second / 50.
How do I check that it meets the WCAG criteria?
Pages can be checked for flickering using a flickering check tool. Those pages which have no flickering elements will pass. Flickering elements which are not in the critical range will be deemed to have passed. Flickering elements in the critical range or close to peak sensitivity will fail.
Checkpoint 7.2 - 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)
Animated gifs or multimedia can be distracting for cognitively impaired, attention deficit and epileptic individuals, particularly when they blink.
How do I do it?
Text should not be marked up to blink with the use of the <BLINK> or <marquee> tags.
How do I check that it meets the WCAG criteria?
Pages should be visually checked for blinking animation. Where this occurs, pages should be scanned for the <BLINK> and <marquee> tags using the Edit > Find tool in Dreamweaver or Notepad.
Checkpoint 7.3 - Until user agents allow users to freeze moving content, avoid movement in pages
How do I do it?
Don't have any moving elements in the page unless users can turn the animation off. When creating Flash or Director Shockwave always have a user controlled pause button. This can simply trigger the play head to jump to a static frame. For more information on navigation with Lingo, the Director language, visit http://www.ilikecake.net/director/lingo02_navigation_with_markers.htm
How do I check that it meets the WCAG criteria?
Run your page through webXact's accessibility checker to validate this checkpoint automatically.
Checkpoint 7.4 - Until user agents provide the ability to stop the refresh, do not create periodically auto-refreshing pages
Auto refreshing pages may cause screen readers to begin over again at the start of the page, as if a new page had been loaded. This can be very frustrating to screen reader users. There are other reasons not to use auto refresh, which you can read at Why Not To "META-Refresh". It's also worth having a look at Why To META-Refresh available on the same page.
How do I do it?
Just don't use the <META> refresh below.
CONTENT="30; URL=http://www.yoursite.com/some/place/">
How do I check that it meets the WCAG criteria?
Run your page through webXact's accessibility checker to validate this checkpoint automatically.
Checkpoint 7.5 - Until user agents provide the ability to stop auto-redirect, do not use markup to redirect pages automatically. Instead, configure the server to perform redirects
How do I do it?
Rather than using an using an auto redirect (see one at http://www.javascriptkit.com/script/script2/autofresh.shtml), simply input a text link to the new page, or configure your server to automatically redirect.
If a page is using an auto redirect, you will see it for a few seconds before another page loads.
How do I check that it meets the WCAG criteria?
This checkpoint was not triggered by any sites I checked with webXact, so I do not know whether it will automatically check this for you, however as it checks checkpoint 7.4, it probably will also check checkpoint 7.5.
