Web Accessibility

Scenarios

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W3C Web Accessibility Criteria

The W3C Web Accessibility Initiative has created several scenarios where accessible sites are important, each focusing on a particular disability. The W3C scenarios pay particular attention to the following three criteria:

  1. The nature of the disability;
  2. Available tools to enhance accessibility for that particular disability; and
  3. Barriers to accessibility faced by that group.

The W3C scenarios outlined below are:

Note: the information in these materials focuses more on visual impairment because of the heavy reliance on graphic interface on the Web today. Future problems with hearing impairment may be more significant, as use of content-rich audio techniques on the Web increase.

Disability Type Comparison
Disability Type Nature of the Disability Barriers Tools to Overcome Barriers
Color blindness Color blindness is a lack of sensitivity to certain colors. Common forms include difficulty distinguishing between red and green, or between yellow and blue. Sometimes color blindness results in the inability to perceive any color.
  • Color used as a unique marker to emphasize text.
  • Text that inadequately contrasts with background color or patterns.
  • Browsers that do not support user override of authors' style sheets.

Style sheets which override the font and background color choices of the author.
Blindness Blindness involves a substantial, uncorrectable loss of vision in both eyes.
  • Images without ALT text.
  • Complex images (e.g. graphs or charts) not adequately described.
  • Video not described in text or audio.
  • Non-linearized tables (i.e. do not make sense when read serially or cell-by-cell).
  • Frames.
  • Forms without logical tab sequence, or that are poorly labeled.
  • Browsers which lack keyboard support for all commands.
  • Screen readers: software which reads text on the screen and outputs the text to a speech synthesizer and/or refreshable braille display.
  • Text-based browsers such as Lynx.
  • Voice browsers, instead of a graphical user interface browser plus screen reader.
Low vision

Four of the many types of low vision (or "partial sight") are:

  • Poor acuity: vision that is not sharp.
  • Tunnel vision: seeing only the middle of the visual field.
  • Central field loss: seeing only the edges of the visual field.
  • Clouded vision.
  • Web pages with absolute font sizes which do not reduce or enlarge easily.
  • Web pages which lose context when enlarged due to inconsistent layout.
  • Web page or images with poor contrast, and whose contrast cannot be changed through override of style sheets.
  • Imaged text which cannot be rewrapped.
  • Many barriers listed for blindness, depending on the extent of visual limitation.
  • Extra-large monitors and/or increasing system font and image sizes.
  • Screen magnifiers or screen enhancement software.
  • Specific combinations of text and background colors (e.g. 24-point yellow font on a black background).
  • Certain typefaces especially legible for particular vision requirements.
Deafness Deafness involves a substantial uncorrectable impairment of hearing in both ears. Some deaf individuals may or may not read or speak a language fluently.
  • Lack of captions or transcripts of audio files on the Web.
  • Lack of content-related images in text-intensive pages. Images can aid comprehension for those whose first language is signed instead of spoken or written.
  • Requirements for voice input on Web pages.
  • Captions for audio content.
  • User ability to toggle audio file captions on and off while browsing Web pages.

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