The Internet is a highly complex network of different technologies. When an item of electronic mail is sent from one address to another, it may pass through dozens of mail servers on the way. Each of these servers may well be running a different operating system. The software that you might use to send email does not have to be the same as the recipient's software.
Web designers are already familiar with making pages that can be displayed on different computing platforms. They know about the "safe" 216-colour palette that renders identically on the PC and the Mac. The techniques of accessible web design simply carry this concept one stage further.
The Department of Trade and Industry (DTI) says:
The principle of "Design for All" is not being widely adopted. It could bring benefits not only to those with special needs but also to able bodied people ... Our research indicates that, whilst many features already exist which could help the elderly and people with disabilities, the awareness of their existence is very low.
-- Information and Communications Technology for the Elderly and People with Disabilities: the Supply Industry's Approach
This report was published in October 1998. You can order it from the DTI by calling their Publications Orderline on 0870 150 2500, quoting publication reference number 98/992, or go to http://www.dti.gov.uk.
Why should you take the trouble to make your website accessible? For the same reason that you would want to make a building accessible - so that it can be used by the maximum possible number of people.
The majority of Internet users use either Microsoft Internet Explorer or Netscape Navigator for their Web browsing. But not everyone can operate standard computer equipment: blind users will not be able to read text from the screen. Luckily, they can use "alternative user agents", a speech synthesiser for example.
Similarly, hardware devices consisting of a series of Braille "cells" can be used to transform Roman characters into a pattern of raised dots. Some user agents allow quick navigation from "header" to "header" within a hypertext document. Others collate and summarise the hyperlinks in an easily-reachable list.
It is clear that not all websites will be able to be viewed using these devices. If your headings and subheadings are declared in a nonstandard way, the "quick navigation" features will be useless. There are a number of other steps you can take in order to take advantage of the capabilities of alternative user agents: see the next section for more information.
The World Wide Web Consortium (W3C) is the public body which regulates several Internet standards, such as the specification for HTML (Hypertext Markup Language). One subgroup, the Web Accessibility Initiative (WAI) has been active in promoting techniques of accessible web design.
W3C-WAI defines three levels of compliance to their guidelines: A, AA, and AAA. There is no formal certification programme, meaning that there is no way to be sure whether a site is in fact compliant to the claimed level. Even so, this marking has gained some respect among the online community.
For more information, visit the W3C website.