Question 7: Can users control scrolling or changing content?
What does this mean?
Web developers often use blinking or scrolling text or animation to draw attention to particular content. Also, content can be set to automatically change or redirect users to another page within a specified length of time. When using such features, ensure they can be paused or stopped by users.
Why does this present a problem?
Some individuals with visual impairments or cognitive disabilities cannot read moving text quickly enough and most screen readers are not able to read moving text at all. Individuals with mobility impairments may not be able to respond quickly or accurately enough to respond to moving objects. Movement can be annoying or distracting to any reader.
What are the solutions?
1. Eliminate flickering screens
- Features, such as applets, plug-ins, scripts, and animated images and movies, may cause the screen to flicker. Quick motion and sudden changes in colour can have this effect.
TIP People with photosensitive epilepsy can have seizures triggered by flickering or flashing in the 4 to 59 flashes per second (Hertz) range with a peak sensitivity at 20 flashes per second. Quick changes from dark to light (like strobe lights) can also trigger seizures. [From WebAIM www.Webaim.org/tutorials/usercontrol]
American legislation, Section 508 of the Rehabilitation Act further specifies not using frequencies between 2 and 55 Hz. [From http://www.access-board.gov/508.htm]
2. Avoid blinking text
- Use other ways to highlight text, such as presentation markup. For example, the following style sheet properties can be used to style text:
- Case: "text-transform" (for uppercase, lowercase, and capitalization)
- Underline, overline: "text-decoration"
- If text must be highlighted by causing it to flash on and off, then use the style sheet 'text-decoration: blink' attribute. Using style sheets will allow users to stop the effect.
- Do not use the <BLINK> and <MARQUEE> elements as they are not defined by W3C (refer also to Question 11).
TIP Some screen readers are unable to read blinking text. They may stick on the text and read it repeatedly, or they may freeze the entire computer system.
3. Make moving content stoppable
- Moving content, such as scrolling text, can be distracting and interfere with an individual's ability to focus on relevant content or the individual may read more slowly than the scrolling speed. It is important that users be able to freeze the movement of text.
- When content must move, provide a mechanism within a script or applet to allow users to freeze motion or updates. Use style sheets with scripting to enable users to turn off or override the motion.
4. Avoid auto-refresh
- Do not cause pages to auto-refresh with "HTTP-EQUIV=refresh" until various Web browsers and assistive technologies allow individuals to turn off the feature.
In the following inaccessible example, the page would refresh or reload itself every 60 seconds:
<HEAD>
<META http-equiv="refresh" content="60">
</HEAD>
<BODY>
<P>Main Page</P>
</BODY>
- Automatically refreshing pages can be disorienting to some users. Instead, when using a continually updated page, inform the users that they should reload the page often.
- If using auto-refresh is unavoidable, provide a single line of text at the top of the page stating that the page contains changing information and will automatically reload itself after a certain amount of time. Also, provide a link to the next screen for those browsers that don't support the feature.
5. Avoid auto-redirect
What is the bottom line?
The bottom line, as stated in WCAG Guideline
7, is give the user control of time-sensitive content changes.
