Everybody accesses the internet in different ways. An individual's needs determine whether they have to change browser settings to view your page or use assistive technologies. People may also use different platforms, ranging from Personal Computers (PCs) to Personal Digital Assistant's (PDAs) or mobile devices such as a phone.
Assistive technology
Access technologies are a key tool to any web developer when checking their site for accessibility. Understanding of these technologies goes hand in hand with understanding the requirements of accessible web design when ensuring that websites meet the Website Accessibility Initiative (WAI) requirements.
There are a great number of assistive technologies that people use. These include alternative user input devices for those who cannot operate a standard keyboard or mouse, screen readers and refreshable braille displays, screen magnification and text-based browsers. Most work together with graphics browsers and, as with graphics browsers, are built to work with standardised World Wide Web Consortium (W3C) technologies such as HTML 4.
How assistive technologies work
This section gives an outline of assistive technologies and how they output the content and functionality of web pages. Details of specific problems each technology may encounter are identified as well as the groups of people likely to use the technology. Understanding how people view pages with various assistive technologies underpins understanding the relevance of each WAI guideline and how to test your site.
Further details about the assistive technologies covered in this section can also be found in the
testing section, which outlines how designers can use these as tools to test their websites.
For more information on
assistive technology please refer to the technology section of the RNIB site.
Three of the main types of technologies used are covered in this section.
Speech and braille output software
Screen readers, also known as audio output and speech output, are used by people who are blind to "listen" to web pages.
A screen reader and refreshable braille display is a software which works together with the platform and software on a standard monitor. Screen readers output aurally what you would otherwise see. This includes everything from start up screens, desk top and tool bars, all software packages and browsers.
When browsing screen readers work with standard browsers to read the content elements on any given web page.
Unlike the eye, which can scan a page to pick out information, a screen reader linearises a page. Put simply, a screen reader will read the outputted page from top to bottom left to right.
In terms of the page's coding this means a screen reader will read the HTML code, from the top, reading only the content, structural coding and textual values of some attributes. This means the screen reader will identify a piece of text as a heading if it is coded using H1, for example, and will read out alternative text used for images (alt text), page titles, summaries, lists and so on. So all structural information that can be gained visually can also be gained aurally as well as the content itself.
Screen readers and refreshable braille displays are one software package. To use the braille output, a braille keypad hardware is attached to the length of a keyboard and small pins are pushed up to output the content in braille.
Popular screen readers and refreshable braille displays are Jaws, WindowEyes and Hal. To find out more have a look in the assistive technology section of the useful links page.
How it works
People rely solely on the keyboard to navigate around a page using various keyboard commands. Being a non-visual medium it is not possible to use a mouse. When a page downloads in a browser the screen reader will start reading the page starting with the title in the title bar, URL and then the page content.
To navigate the page the tab key can be used to tab from one element to the next, up or down. This includes all types of images, links, form fields, buttons, objects and so on. Other commands exist such as listing the links in a page, frame headings and the page headings. The screen reader will identify each element as it reads it out, for example if it is a link to "About us" the screen reader will say "Link, About us", if it is a graphic that is a button for "Go" it will read "Button, go".
Accessibility issues
Good use of alt text, clear link text and correctly coded headings are crucial to navigation. The image of a dialogue box taken in Jaws shows list links on a website that have not been given distinct link text. There are eight instances of the link text "read" all of which are linked to different pages. When heard out of context, as they will be when the tab key is used to navigate, they give no clear indication of what the page will be.
Screen magnification software
As with screen readers and refreshable braille displays, screen magnification software works together with the operating system and web browser to enlarge the contents. Generally this is very large, and far exceeds the largest settings that a standard operating system has in its settings. It is the software of choice amongst people with low vision.
How it works
Screen magnification does just what it says, and simply magnifies the screen. The degree of magnification can vary according to the preferences of the person using it. The greater the level of magnification required results in less information that can be displayed on screen. In some instances the magnification can be so extreme that only two or three words are displayed on the screen at a time.
Most people who use screen magnification also change the contrast and colour settings to make it easier to read. For example, they may set a black background with white text to make it stand out more.
Accessibility essentials
There are a number of issues to be considered for people who use screen magnification. A major drawback, but one that is easy to rectify, is where there are large areas of blank space between text and elements. This need to scroll through large areas of blank space can make it very difficult for someone to find elements in a page with ease. They may not even realise that there is anything to find at the other end of a large blank space, and simply assume it is the end of the content.
For example, imagine a form where the text labels such as "Name" have too much space between it and the text input box. Good judgement is essential in laying out page and the elements it contains.
Images also do not scale well, and become blurred and pixelated when magnified. This can cause problems of legibility if these are images of text. For example, navigation could become incomprehensible and unusable if images of text is used as links.
The following example shows how an image of text begins to break up when magnified just a few times. This distortion effect will increase dramatically with the extreme magnification that is commonly used by someone with low vision:
Clear and consistent layout is also very important for people who depend on screen magnification. Having navigation links in the same place on each page helps people gain familiarity with the site, and helps them learn where information can be found quickly. Inconsistent layout and navigation can be extremely frustrating, and so should be avoided.
Text browsers
Text-based browsers are just that. They simply display the contents of the page as text. They do not support images, JavaScript, Java, CSS (Cascading Style Sheets), plug-ins or dynamic HTML. As such they are extremely fast when browsing the web. They are also excellent tools when testing your site for accessibility.
Lynx is the most popular text-based browser. It works on Unix, DOS and Windows via DOS emulation. It is available as a free download, or alternatively, you can visit the Yellowpipe site for an online version that allows you to upload your page and see what it looks like in Lynx.
How it works
As with screen readers and refreshable braille displays, text-based browsers render content in a linear fashion. Pages are navigated using a variety of keyboard commands and cannot be interacted with using a mouse. Below is an image of the RNIB home page when viewed in Lynx.
The alternative text for images is seen in place of the images, lines represent text input boxes, square brackets [ ] indicate checkboxes and links are shown in a different colour.
Accessibility essentials
The accessibility of information and making sense of it in a text-based browser is very similar to that of screen readers and refreshable braille displays. Correct and intuitive alternative text must be provided, frames given names and titles, and a logical order of content when read in a linear way.
In the above example "divider", "arrow" and "pixel" are all images used for spacing, layout or decoration. As they have not been given alternative descriptive text, they convey no meaning and can be confusing to read. In this instance, and should have null value alternative text (alt=" "), so that they are ignored by Lynx.