HTML Unleashed PRE. Creating Widely Accessible Web Pages: What We Need

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.