The World Wide Web Consortium (W3C) is an international consortium that developers protocols and guidelines for technologies that work on the web. Tim Berners-Lee, W3C director and inventor of the World Wide Web has famously stated:

The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect.

A group within the W3C called the Web Accessibility Initiative (WAI) develops guidelines that are generally regarded as the international standard for web accessibility. The first version of the Web Content Accessibility Guidelines (WCAG) was published on May 5, 1999. Many organizations and governments have web accessibility policies that reference or are largely derived from WCAG 1.

On December 11, 2008, WCAG 2 became an official recommendation of the WAI. The new version of the guidelines is principle-based and applies to a broad range of web technologies – not just HTML. The guidelines are based around the following 4 principles of accessible content:

Content Must be Perceivable

There are many ways in which web content is perceived. While most people think of the web as a visual medium, web content might be read aloud or accessed via touch using a refreshable braille display. Even for people visually looking at content, there are many different factors which affect perception. Screen size and resolution, browser choice and installed plug-ins, availability of colors, text size, disability, and other factors mean that people “see” content in many different ways.

To be accessible, web content must be designed to be perceivable to a diverse group of individual using a range of devices.

Interface Elements in the Content Must be Operable

People use a variety of input devices to navigate web content. While the mouse is the most common, trackballs, voice input, standard or on-screen keyboards, and other methods may also be used. Have you encountered a situation while surfing the web where you could “see” the content on a page, but a link, menu, form, or other interface element simply didn’t work? For individuals who don’t use a mouse, for instance, fly-out menus that require the user to hover a mouse over a graphic are often not accessible.

To be accessible, interface elements must by accessible to individuals using different types of input devices. In particular, web pages should be usable by someone using only the keyboard.

Content and Controls Must be Understandable

Some websites are both perceivable and operable, but so difficult to understand that they cannot be used effectively. This can result from many factors, including non-standard design practices, a failure to provide help pages, or content that is too complex for the intended audience. The readability of web content continues to pose significant problems. A 2003 Study, Achieving E-Government for All: Highlights from a National Survey, reports that while the average person reads at an 8th grade level, the average readability level of government websites is at the 11th grade. If web content is not easily understandable by users, it is not an effective way to convey information.

To be accessible, content and controls must be understandable and appropriate to the audience for which they are intended.

Content Must be Robust Enough to Work With Current and Future Technologies

It is difficult to predict the details of the computer system, input method, browser choice, and plug-in availability that a web user might bring to your site. It is even more difficult to predict what types of technologies will be used to access web content in 5 years. Web developers and web content authors should strive to make pages that conform to web standards as presented by the W3C. When content requires the use of a particular plug-in or depends upon a technology being enabled, an alternate version should be available for people whose systems do not support the supplementary technology. For instance, if JavaScript is used to provide a pop-up window to alert the user of an invalid e-mail address, a similar alert should be available after submitting a form for users who have JavaScript disabled. By adhering to common standards in markup language, and designing sites to degrade gracefully when certain technologies are not available, content is more likely to be accessible now and in the future.

To be accessible, content needs to be robust enough to work in a variety of technology environments, and should adhere to common standards defined by the W3C.