Accessibility - Display
Blinking, Moving, or Scrolling Content
Until user agents| allow users to control movement or stop refresh and auto-redirect, avoid moving, blinking, scrolling, or auto-updating objects| or pages. [Note that the BLINK and MARQUEE elements are not defined in any W3C HTML specification and should not be used]
Ensure that moving, blinking, scrolling, or auto-updating objects or pages may be paused or stopped. Some people with cognitive or visual disabilities are unable to read moving text quickly enough, if at all, and screen readers are unable to read moving text. Displays which flicker or flash can trigger seizures in people with photosensitive epilepsy, particularly if the flash has a high intensity and is within the frequency range between 4Hz and 55Hz. This includes flashing text, turning graphics on and off or repeatedly changing between different images on the screen. Currently, user agents do not allow users to control screen flickering or blinking or to stop the refreshing of pages, so you should avoid using elements that cause movement or automatic refreshing of pages.
Accessibility aside, many users will not wait to read a marquee scroll, so the message you are trying to convey may not be read. Many also find the marquee element and blinking text irritating.
If movement is necessary:
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If moving content is used, provide a mechanism within a script or applet to allow users to freeze motion
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Use style sheets to create movement (using the CSS, 'text-decoration: blink'; attribute) so that the user has the ability to turn off the movement by turning off the style sheet
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Do not use the proprietary HTML BLINK and MARQUEE elements
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Minimize the area of the screen that is moving - smaller areas are less likely to cause seizures
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Avoid high intensity flashing
Do not use markup to redirect pages automatically
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Do not use code which might automatically load a new page xx seconds after you load the current page. This markup is nonstandard, it disorients users and it can disrupt a browser's history of visited pages.
<META http-equiv="refresh" content="5" "http://www.bolton.ac.uk/newpage">
Instead of automatically reloading a page, authors should:
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Configure the server to use the appropriate HTTP status code
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Replace the page that would be redirected with a static page containing a normal link to the new page.
Do not create periodically auto-refreshing pages
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Instead of reloading the page automatically for the user, if your page is being continually updated then inform the user that they should reload the page often.
For example, in HTML, don't cause pages to auto-refresh with "HTTP-EQUIV=refresh" until user agents allow users to turn off the feature. The following code would cause the same page to "refresh" or reload itself every 60 seconds. Presumably you would do this because you are changing the content of that page frequently.
The following example should not be used because it does not allow the user the ability to control when the page is refreshed.
<META http-equiv="refresh" content="60">
<BODY>
<P>...Information...
</BODY>
Testing for moving content
View the page with a graphical browser. Ensure that there is no blinking, flickering, or movement on the page. If using style sheets to convey movement, disable the style sheet (to do this in Netscape, go to Edit-Preferences-Advanced and uncheck 'Enable Style Sheets') to verify that the movement can be turned off.
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