HTML and CSS Reference
In-Depth Information
Markup Requirements for Nontext Content
Images, photos, graphics, and symbols can be applied to improve user experience and help the user understand the
content. However, all nontext contents, such as images, embedded objects (Flash content, applets, audio, video, and
so on), ASCII arts , emoticons , and leetspeaks must have alternate texts.
All images must have an alt attribute. For those images that can be safely ignored by assistive technology, the
title attribute must be omitted and the alt text set to null ( alt="" ). If an image and its associated text have the same
link, they must be combined in order to avoid unnecessary duplication.
Spacer images such as 1×1 pixel GIF files should be totally eliminated in favor of CSS margins and padding.
For those images and objects where a short description is not sufficient, a long description must be added using
the longdesc attribute or a regular a element with a link to the description.
Nontext content represented in colors must also be available with patterns that can be understood without
colors.
Alternate text must be provided for nontext content that identifies its purpose (even for the content that requires
sensory experience). Additionally, both a short and a long description must be provided for nontext content with an
identical purpose that presents the same information.
If the original nontext content is too long or the same information cannot be achieved with text alone, short
alternate text must be written that briefly summarizes the nontext content.
Images used exclusively for decoration, such as background images, image rollovers, or tab images, must be
provided using CSS. Since there is no additional markup, assistive technology can ignore this nontext content.
Alternate text must be written for all area elements within image maps.
A text or nontext alternative must be provided for all objects. Alternate texts can be written directly in the content
of the object element. Nontext alternatives can be provided by nested objects.
Adjacent nontext content sharing information or functionality must be described by alternate text in order to
avoid unnecessary duplication.
Blinking and Flashing Content
Photoepileptic seizures caused by strobing or flashing effects should be eliminated. A link or button must always be
added to web pages with blinking content that loads equivalent pages without blinking content. Blinking contents
can be included on web pages only by using a technology that provides the option to turn off blinking with a browser
feature. Blinking content must be minimized below 5 seconds using scripts and, if possible, totally eliminated. The
same holds for animated GIF images.
Flashing content must also be minimized. A maximum of three flashes is allowed within 1 second. If it is not
feasible because of the content features, the flashing area must be less than 25 percent of 10 degrees of the visual field.
The content is not allowed to violate the general flash threshold or red flash threshold, which avoids photosensitive
seizures. There are tools, such as the Photosensitive Epilepsy Analysis Tool (PEAT) [37], that can be used to evaluate
flashing content to reduce the risk of seizure.
Flash Objects
The dimensions of embedded Flash objects may be specified in relative units ( em or % ).
Nontext objects marked with the name property must be applied in Flash to allow assistive technology to access
them. A long text alternative must be provided by the description property for nontext objects in Flash. Text
alternatives must be provided for clickable image hotspots that serve the same purpose. The accessible description of
DataGrids has been used for years to provide information readable by screen readers.
Flash graphics must be marked in a way that they can be ignored by assistive technology if needed. This can be
accomplished by directly exploiting the accessibility features of Flash objects or by applying textual alternatives using
ActionScript.
If adjacent text and image buttons (icons) serve the same purpose, they must be combined into a single button
symbol instance.
 
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