Web accessibility

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“Web accessibility refers to the inclusive practice of making websites usable by people of all abilities and disabilities. When sites are correctly designed, developed and edited, all users can have equal access to information and functionality.” (Wikipedia, retrieved no 18, 2010)

See also: web usability, usability, ergonomics and cognitive ergonomics

Web Content Accessibility Guidelines

Several "players" create web accessibility guidelines. The major ones are W3C and the US government.

The first well known guidelines focused on content:

These guidelines explain how to make Web content accessible to people with disabilities. The guidelines are intended for all Web content developers (page authors and site designers) and for developers of authoring tools. The primary goal of these guidelines is to promote accessibility. However, following them will also make Web content more available to all users, whatever user agent they are using (e.g., desktop browser, voice browser, mobile phone, automobile-based personal computer, etc.) or constraints they may be operating under (e.g., noisy surroundings, under- or over-illuminated rooms, in a hands-free environment, etc.). Following these guidelines will also help people find information on the Web more quickly. These guidelines do not discourage content developers from using images, video, etc., but rather explain how to make multimedia content more accessible to a wide audience. Web Content Accessibility Guidelines 1.0 retrieved 12:57, 4 June 2008 (UTC).

Later work at W3C was split into three different types of guidelines, reflecting the fact the web has become an universal and ubiquitous software platform: Web Content Accessibility Guidelines (WCAG), Authoring Tool Accessibility Guidelines (ATAG), and User Agent Accessibility Guidelines (UAAG).

WCAG 2.0, i.e. the 2008 version of web content accessibility is formulated in more general and technology-independent terms:

  • Perceivable - Information and user interface components must be presentable to users in ways they can perceive. This means that users must be able to perceive the information being presented (it can't be invisible to all of their senses)
  • Operable - User interface components and navigation must be operable. This means that users must be able to operate the interface (the interface cannot require interaction that a user cannot perform)
  • Understandable - Information and the operation of user interface must be understandable. This means that users must be able to understand the information as well as the operation of the user interface (the content or operation cannot be beyond their understanding)
  • Robust - Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies. This means that users must be able to access the content as technologies advance (as technologies and user agents evolve, the content should remain accessible)
Introduction to Understanding WCAG 2.0 retrieved April 17 2011.

Users with accessibility problems

According to wikipedia one may distinguish several types of impairments:

  • Visual: Visual impairments including blindness, various common types of low vision and poor eyesight, various types of color blindness;
  • Motor/Mobility: e.g. difficulty or inability to use the hands, including tremors, muscle slowness, loss of fine muscle control, etc., due to conditions such as Parkinson's Disease, muscular dystrophy, cerebral palsy, stroke;
  • Auditory: Deafness or hearing impairments, including individuals who are hard of hearing;
  • Seizures: Photoepileptic seizures caused by visual strobe or flashing effects.
  • Cognitive/Intellectual: Developmental disabilities, learning disabilities (dyslexia, dyscalculia, etc.), and cognitive disabilities of various origins, affecting memory, attention, developmental "maturity," problem-solving and logic skills, etc.;

Some of you may think that you can ignore these populations since they are small. Besides ethical questions, also consider that you may be in situations where you are disabled:

  • Visual: You drive a car and wish to consult the latest news in your favorite technical blog, so you want an audio browser.
  • Motor: You try to view web pages on your cell phone ;)
  • Auditory: You are in a boring meeting or a class and want to "listen" to news, you need an alternative to sound.
  • Cognitive/Intellectual: You are drunk and/or really tired, but need to repair a server. So the help text you will have to read got to be both simple and effective.

Assistive technology

According to WAI's How to Make Presentations Accessible to All (retrieved nov 24 2010), “Assistive technologies are software or equipment that people with disabilities use to improve interaction with the web, such as screen readers that read aloud web pages for people who cannot read text, screen magnifiers for people with some types of low vision, and voice recognition software and selection switches for people who cannot use a keyboard or mouse.”


Analysis of accessibility compliance
  • WAVE is a free web accessibility evaluation tool provided by WebAIM. It is used to aid humans in the web accessibility evaluation process. Rather than providing a complex technical report, WAVE shows the original web page with embedded icons and indicators that reveal the accessibility of that page. Either as online form or as Firefox toolbar.
  • TAW3 online, tool for the analysis of Web sites, based on the W3C - Web Content Accessibility Guidelines 1.0 (WCAG 1.0)
  • UITest.com. This is an all-in-one service for accessibility, validity and miscellaneous. Enter a URL and the do checking using various other services.
General user-assistive products
  • NVDA NonVisual Desktop Access (NVDA) is a free and open source screen reader for the Microsoft Windows operating system. Providing feedback via synthetic speech and Braille, it enables blind or vision impaired people to access computers running Windows for no more cost than a sighted person. Major features include support for over 20 languages and the ability to run entirely from a USB drive with no installation.
  • Freedom Scientific produces a wide palette of blindness and low vision products, e.g. the popular JAWS for Windows Screen Reading Software. Some products are available as Trial Software
Browser extensions (both analysis and assistive)
  • Opera 11 has support for voice browsing. It probably isn't very appropriate for blind folks. The module must be installed (instructions included in the link)
  • Fangs is a Mozilla Firefox extension that creates a textual representation of a web page similar to how the page would be read by a modern screen reader. I.e. an accessibility researcher can read the text instead of listing to it ....
  • taw. Firefox extension. allows to verify, with just a click, the accessibility of the Web sites that you are visiting, by means of the TAW3 online service (tawdis.net) and making use of the W3C Web Content Accessibility Guidelines (WCAG 1.0 and WCAG 2.0). (spanish/catalan/galego,somewhat English).
  • AccessibleNews Firefox plugin to make more accessible to Blind Users. Registration needed. The basic version is free.
  • LowBrowse Firefox plugin to make browsing more accessible to users with low vision. (not available for Firefox 4.0)
  • Reader helps you read more of the web by transforming text on any website using fonts, colors, and layouts of your choosing. Exists by default in Safari.

Standards and Issues


There are three major sets of guidelines:

  • WCAG 1.0 - The former W3C recommendation
  • WCAG 2.0 - The current W3C recommendation
  • Section 508 - A US standard for government web sites

We shall introduce these below.

See also Guidelines-based review (for checklists) and Introduction to Web Accessibility at WebAIM (Web Accessibility in mind). Excellent introduction. Also includes videos and links.

W3C recommendations

A first version of the web content guidelines (and that is still frequently cited) was published in 1999 as Web Content Accessibility Guidelines 1.0 (WCAG), W3C Recommendation 5-May-1999

WCAG 2.0 became a formal recommentation (standard) in december 2008. According to the WCAG Overview (retrieved 16:37, 24 November 2010 (CET)), version 2 of the Web Content Accesssibility Guidelines “has 12 guidelines that are organized under 4 principles: perceivable, operable, understandable, and robust. For each guideline, there are testable success criteria, which are at three levels: A, AA, and AAA.”. This standards document is completed by four supporting documents:

The relationship between these four texts is explained in The WCAG 2.0 Documents and its following figure:

WCAG 2.0 documents, copyright © W3C

Since all of these texts are fairly long, there are various summaries and introductions, in particular:

Overviews of various work at W3C

Whereas the WCAG 1.0 guidelines could be summarized with a short of list of instructions, the WCAG 2.0 guidelines are summarized by W3C/WAI with general technology-independent principles:

WCAG 1.0 Quick Tips (deprecated)

  1. Images & animations': Use the alt attribute to describe the function of each visual.
  2. Image maps. Use the client-side map and text for hotspots.
  3. Multimedia. Provide captioning and transcripts of audio, and descriptions of video.
  4. Hypertext links. Use text that makes sense when read out of context. For example, avoid "click here."
  5. Page organization. Use headings, lists, and consistent structure. Use CSS for layout and style where possible.
  6. Graphs & charts. Summarize or use the longdesc attribute.
  7. Scripts, applets, & plug-ins. Provide alternative content in case active features are inaccessible or unsupported.
  8. Frames. Use the noframes element and meaningful titles.
  9. Tables. Make line-by-line reading sensible. Summarize.
  10. Check your work. Validate. Use tools, checklist, and guidelines at http://www.w3.org/TR/WCAG

WCAG 2.0 principles

(with links to sections of the How to Meet WCAG 2.0 document, a customizable quick reference to Web Content Accessibility Guidelines 2.0 requirements (success criteria) and techniques.

1.1 Provide text alternatives for non-text content. Read Text Alternatives: Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.
1.2 Provide captions and other alternatives for multimedia. Read Time-based Media: Provide alternatives for time-based media.
1.3 Create content that can be presented in different ways, including by assistive technologies, without losing meaning. Read Adaptable: Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
1.4 Make it easier for users to see and hear content. Read Distinguishable: Make it easier for users to see and hear content including separating foreground from background.
2.1 Make all functionality available from a keyboard. Read Keyboard Accessible: Make all functionality available from a keyboard.
2.2 Give users enough time to read and use content. Read Enough Time: Provide users enough time to read and use content.
2.3 Do not use content that causes seizures. Read Seizures: Do not design content in a way that is known to cause seizures.
2.4 Help users navigate and find content. Read Navigable: Provide ways to help users navigate, find content, and determine where they are.
3.1 Make text readable and understandable. Read Readable: Make text content readable and understandable.
3.2 Make content appear and operate in predictable ways. Read Predictable: Make Web pages appear and operate in predictable ways.
3.3 Help users avoid and correct mistakes. Read Input Assistance: Help users avoid and correct mistakes.
4.1 Maximize compatibility with current and future user tools. Read Compatible: Maximize compatibility with current and future user agents, including assistive technologies.

US government standards

In 1998, Congress amended the Rehabilitation Act of 1973 (29 U.S.C. 794d) to require Federal agencies to make their electronic and information technology (EIT) accessible to people with disabilities.

Summary of 1194.22 Web-based intranet and internet information and applications:

(copy/paste from the source)

(a) A text equivalent for every non-text element shall be provided (e.g., via "alt", "longdesc", or in element content).

(b) Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation.

(c) Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup.

(d) Documents shall be organized so they are readable without requiring an associated style sheet.

(e) Redundant text links shall be provided for each active region of a server-side image map.

(f) Client-side image maps shall be provided instead of server-side image maps except where the regions cannot be defined with an available geometric shape.

(g) Row and column headers shall be identified for data tables.

(h) Markup shall be used to associate data cells and header cells for data tables that have two or more logical levels of row or column headers.

(i) Frames shall be titled with text that facilitates frame identification and navigation.

(j) Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz.

(k) A text-only page, with equivalent information or functionality, shall be provided to make a web site comply with the provisions of this part, when compliance cannot be accomplished in any other way. The content of the text-only page shall be updated whenever the primary page changes.

(l) When pages utilize scripting languages to display content, or to create interface elements, the information provided by the script shall be identified with functional text that can be read by assistive technology.

(m) When a web page requires that an applet, plug-in or other application be present on the client system to interpret page content, the page must provide a link to a plug-in or applet that complies with §1194.21(a) through (l).

(n) When electronic forms are designed to be completed on-line, the form shall allow people using assistive technology to access the information, field elements, and functionality required for completion and submission of the form, including all directions and cues.

(o) A method shall be provided that permits users to skip repetitive navigation links.

(p) When a timed response is required, the user shall be alerted and given sufficient time to indicate more time is required.

These are quite similar as the WAG guidelines, but paragraphs (l), (m), (n), (o), and (p) impose extra constraints.


Bodies and organizations



  • Web Accessibility Gone Wild some really useful discussion of a variety of mistakes, misconceptions, over-indulgences, intricacies, and generally silly aspects of modern accessibility. At webaim.org

Understandable & reasonably sized checklists

Introductory videos and slides

Web sites

  • WebAIM. (Probably) the best one-stop place for all questions around accessibility. Introductions, standards, legal norms, tools.

More from W3C / WAI

W3C Web Accessibility initiative's Presentation and Training material, includes: