HTML and CSS Reference
In-Depth Information
Flash Accessibility
Although accessibility was a weak point of the Flash technology for years, eventually both the developer environment
and the free player had been improved. Adobe Flash Professional and Adobe Flash Player have several features to
support assistive technology.
The layout and structure can be rather complex in Flash movies, making it very difficult for screen readers to read
the content. A description added for the entire movie can give hints for screen readers about the movie structure.
Text equivalents must be added for graphic elements such as names for graphic icons or descriptions for
gesturing animations. Element groups must have a single text equivalent.
Movies that never stop moving cause screen readers to refresh frequently. Even on web pages that contain a
movie at the bottom, screen readers might interpret motion as a page update and return to the top to start reading
again. This behavior can be eliminated by making the child objects of movie clips or entire movies inaccessible [47].
To allow users to control motion, Next buttons must be added to movies instead of displaying information for a
limited time.
Several user interface components are accessible in Flash that automate common accessibility tasks such as
labeling or providing keyboard access. The accessibility object can be enabled with the class enableAccessibility() .
The FLVPlayback component provides the option to include a video player in Flash applications to play
downloaded Adobe Flash Video (FLV) files and streaming FLV files. The FLVPlaybackCaptioning component
associates captions to your video. The captioning component supports the Timed Text Markup Language (TTML)
W3C standard, along with multiple captioning and toggle control.
There are various approaches for providing control over reading order in Flash such as limiting stage size,
providing an additional, linear version of the content or specifying reading order via ActionScript.
User controls must be accessible through the keyboard. Keyboard shortcuts must be added to buttons. In order to
consider the limitations of screen readers, scripts must be kept within frames and empty movie clips used as buttons
must be avoided.
In Flash Professional CS5, a new component was introduced to display audio captions contained either in Timed
Text format (DFXP) or integrated with the FLV file as cue points. Flash Professional CS5 also added native support for
accessible video player skins.
User controls such as the Play and Pause buttons are mandatory for audio playback.
For all controls, it is important to provide the user with feedback on the control as it changes.
The general rules for color selection described earlier in the WCAG requirements also apply for Flash contents.
Accessibility of Mathematical Notations
Mathematical equations provided in GIF images can be hard to read for the visually impaired and, if provided without
a textual description, are inaccessible for screen readers.
In contrast, MathML equations are accessible. The accessibility potential of MathML is clearly demonstrated
by the accessibility features of a free MathML plug-in for Internet Explorer, 3 Design Science MathPlayer [48]. The
software provides audio or Braille descriptions for mathematical notations to screen readers. MathPlayer also has
native speech capabilities ( speak expression from the local menu). It allows keyboard navigation. MathPlayer 2
also contains MathZoom that allows users to magnify individual expressions. The matching algorithm ensures that
the font size of mathematical notations is increased when the surrounding text is zoomed. Additionally, MathPlayer
supports line breaks, which can improve readability if the font size is increased. It provides synchronized highlighting
of subexpressions that are being read out loud, which helps people with certain learning disabilities such as dyslexia
or dyscalculia
3 Since Internet Explorer has native MathML support from version 9, a MathML plugin is required for earlier versions only.
Design Science also provides tools for creating mathematical notations such as MathType (see section “MathType”).
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