|
 s the Web is primarily a visual medium, vision
problems are the most troublesome from the accessibility
viewpoint. People with low (residual) vision and color-blind
people employ various techniques for improving visibility, such as
increasing color contrast and using large fonts. Those who are
blind have to resort to speech synthesizers or Braille (tactile)
output. Needless to say, none of these methods can
preserve anything but the very essence of web pages' textual
content.
Some people with physical disabilities have trouble using
conventional input devices, most often the mouse. It requires a much
finer motor control to point-and-click with a mouse than to press keys
on a keyboard, so providing a keyboard-only means of input and
navigation is absolutely necessary for a web interface. For the most part,
this is an issue for browser developers to address, although HTML
authors can help too (especially by proper coding of form elements,
see "Forms and links" later in the chapter).
With other kinds of disabilities, accessibility considerations
are relatively less onerous. Deaf users cannot receive audio
information if it's not duplicated by visual means. Cognitive
impairments sometimes impede using navigation mechanisms on a page
even if the content itself is accessible. The requirements of
web users with low-bandwidth or text-only access are also closely
related to the accessibility issue.
There are also situations in which people with full sensory,
physical, and cognitive abilities prefer a non-visual mode of
delivering information---for instance, it may be convenient to listen to
the news when driving a car or walking. Finally, we should remember
about various robots and intelligent agents that, in many aspects, may
be likened to people with disabilities (for example, indexing robots
usually cannot extract any useful information from images and have to
rely on text only; for more on this, see Chapter 43, "Strategies
for Indexing and Search Engines").
Of course, web page authors aren't supposed to supply audio
versions for all text on their pages. Users with disabilities commonly
have the necessary software and hardware (usually called assistive
technologies) to work with computer programs and data, including
web pages. For example, software for speech access to web pages breaks
into speech browsers that interpret the HTML source of web pages
(e.g. pwWebSpeak) and more general
screen readers that just read out the text displayed on the
screen or in a window (e.g. the IBM Screen Reader).
Therefore, we could say that the most realistic goal of a web page
author is to present the content in a way that's easily accessible to the
assistive technologies---in the hope that they will take more
qualified care of the needs of the disabled. Admittedly, sometimes
approaching this goal might involve some decisions justified purely by the features of
particular access devices. Still, most accessibility recommendations
can be derived from a couple of basic principles.
| 
