Fundamentals of the web and disabled users


The purpose of this introductory lesson is to explain web site accessibility, how the web works, and the tools and methods used by disabled people to access the Internet.

What is web site accessibility?

Web site accessibility is an important element in helping to build an inclusive society. In particular, accessible web sites can provide a "life enhancing" experience for disabled people. Properly constructed web sites give disabled people the independence to pay their own bills, do their own shopping, find employment and or training, and the tools to keep in touch with family and friends.

In practice, accessibility means designing and building web sites using agreed standards so that they work on all sorts of platforms (internet browsers, mobile phones, PDAs, screen readers etc.). It also means including some additional elements so that anyone can experience your message, including the elderly and disabled.

On page 2 of this lesson we shall look at the tools and techniques used by disabled people. But we start by reminding ourselves of how the web works.

How the World-Wide-Web works

The Internet is a new, digital medium. At it's simplest the electronic signals are sent over the Internet and converted into text and numbers by a computer, mobile phone, screen reader or other device. To make the page more interesting to visual users the page can import images, applications and styles. These imports support the text but they must not replace it.

Because it is a digital medium, the web allows much more flexibility than traditional media such as paper. There is no need for the author to provide large text versions or audio tapes of their content. The user's computer can convert the content into any format that the user requires (e.g. large print, audio, Braille, or high contrast). This makes the web an extremely efficient method of communication and one that offers disabled people full inclusion in the new "Information Society".

When Sir Tim Berners Lee invented the World-Wide-Web his aim was to allow a simple text document to link to other documents on the Internet so that researchers could share information more effectively. These links (called "hyperlinks") could also import images and other media into the basic page. The core of these web pages has always been the HTML document. This document is written in plain ASCII text (i.e. just the characters available on a standard keyboard) and should contain all the information that you want to impart to your visitors.

The diagram below shows the relationship between the HTML page and any images, style sheets or other media.

Diagram illustrating the page components

A web browser or other suitable technology interprets the code elements between the < > brackets in order to understand the structure of the page and thus to display the body text on the user's screen or read the text out loud through a speaker.

It should be clear from the above that the key to the World-Wide-Web's phenomenal success is it�s simplicity. A set of basic standards for the underlying HTML code gives the web its tremendous robustness and flexibility.

The governing body for the design and application of these standards is the World-Wide-Web Consortium (W3C) who publish the internationally agreed standards on their web site ( Software developers use these standards when designing Internet browsers, assistive technologies such as screen readers, mobile phone applications, search robots and anything else designed to work with web content. Web-designers who want their sites to be useable on all these platforms needs to apply these standards accurately and efficiently. The two recommended standards are HTML4.0 and XHTML 1.0. There is very little difference between these two standards, but if you have the choice then XHTML1.0 is more robust (but is less forgiving). The examples in these lessons are all written using the HTML4.0 standard, but will work equally as well in an XHTML1.0 environment. Links to the W3C web site are given at the end of the lesson.

Avoiding barriers

Providing that the engineering task (writing valid HTML code) is undertaken correctly, any form of Internet technology such as a browser or screen reader will read any single web page. There are just three potential barriers to universal accessibility that remain,

  1. When you introduce additional items to a page, such as images, animations, video or scripted applications, you do not prevent the basic HTML working as it should.
  2. When you use interactive elements such as forms you ensure that the controls work with the full range of input devices (primarily both the keyboard and the mouse).
  3. The links to other web pages and and documents are logical and the overall navigation is intuitive so that users can follow an intelligent route through your content.

This set of lessons is designed to help you avoid creating these barriers to accessibility whilst still delivering an effective and interesting web site. Before we start, however, we will have a look at how disabled people use the web.