Stanford Online Accessibility Program

Defining Universal Web Accessibility

The different types of impairments / barriers

When we speak about web accessibility we must acknowledge and understand the various types of impairments and barriers that may impact on how users will interact with your web content. They can be broken down into the following categories:

Visual impairments

Impairments can range from total blindness, to low vision, reduced vision (near sighted / far sighted), as well as colour blindness, etc. Due to the fact that the Internet is often perceived as primarily a visual medium, this is often the easiest of the disabilities to grasp. Clients in this group will usually employ adaptive technology such as Screen readers, screen magnifiers, etc.

Mobility impairments

May include paraplegics / quadriplegics, persons with arthritis, Parkinson's, cerebral palsy, etc., extreme youth, extreme age, or temporary conditions. Clients in this group often employ technology such as speech recognition software, as well as alternate switching devices (sip and puff, foot switches, head activated mouse, one-handed keyboards, etc.)

Auditory impairments

Includes total or partial hearing loss, noisy environments or areas which require silence, appliances without soundcards and/or speakers, etc. Normally associated with Multimedia files on web sites, issues may also arise when required Media Player plug-ins are not present or supported, or conectivity issues impeed the delivery of the media files.

Cognitive impairments

Often the most difficult impairment to address, cognitive disabilities can range from severe learning disability, to low literacy skills, dyslexia or cultural and language differences. While some techniques do exist to aid in web site accessibility, clear, effective, written communication that is target-audience appropriate is important for this group.

Technological restrictions

While not a disability in the traditional sense, this addresses older equipment and poor connectivity, to "cutting edge" appliances such as cell phones, pda's and others.

The need for "Agnostic" development / device independence

In the early days of the internet (pre-1998), Netscape Navigator ruled the web, with an estimated 95% market share. Enter Microsoft and their free web browser Internet Explorer. In less than 3 years Internet Explorer overtook all other comers and today is considered the de facto standard web browser. (Although by today's standard [2006] it's actually surpassed in quality and Standards Compliance by others including Firefox, Safari, and Opera to name just three).

Lesson to learn: hoping or relying on the end user to have a specific browser or other software installed is a false hope, and a potential accessibility issue. Pages designed specifically for Netscape in 1997 often fail or crash in today's newer browsers. Developing to established standards ensures this kind of problem will not happen.

It's not just which browser the end user is viewing your content with; often it may in fact be a different type of device all together. From hand-held devices like PDA's and Computer tablets to stand alone Internet Kiosks, we as developers just cannot rely on end users accessing our content the same way we do. Smart web developers are User Agent Agnostic.

"It works for me..." is just not acceptable anymore.

Understanding/knowing your audience

Most sites are built for an audience, with the audience representing any person who will interact with, view, read, navigate, search on, order from, submit to, download from -- and so on -- the web site. Since practically every measurement of a web site's success involves the audience it makes a great deal of sense to develop a deeper understanding of your audience and use this understanding to design a site that accommodates your end user.

Beyond understanding the motivations or goals of your audience, you must also understand the basic mechanics of how your users will interact with your site:

• How will the site render on a client's user agent (browser)?
• How will the user view the site? Visually? With graphics enabled? With a Braille reader? With a screen reader?
• Will the user's user agent be able to support all of your site's functionality?

Often, the answers to these questions are not self evident, but asking them, and planning for them, is a key step in your development process.

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