This W3C Draft Note is a supporting document for guidelines and
technical work of the W3C Web Accessibility
Initiative (WAI). It provides an introduction to use of the Web by people
with a variety of disabilities for the purpose of better understanding their
requirements when using the Web.
Specifically, this document describes requirements for Web access by people
with physical, visual, hearing, and cognitive or neurological disabilities;
it describes assistive technologies used by some people with disabilities
when accessing the Web; and it provides examples of people with disabilities
successfully or unsuccessfully accessing the Web according to the designs
of Web sites and Web-based applications.
This document is not intended as a comprehensive or in-depth description
of disability, nor of assistive technologies used by people with disabilities.
Additional information on these topics is available by searching on the Web
under many of the terms in this Note.
This document is [not yet] a W3C Note made available by the W3C
Web Accessibility Initiative. This NOTE has [not yet] been jointly
approved by the WAI Education and Outreach Working Group (EOWG), the Web
Content Guidelines Working Group, the User Agent Guidelines Working Group,
the Authoring Tool Guidelines Working Group, and the Protocols and Formats
Working Group (PFWG). This version is offered for WAI EOWG review and has
not yet been reviewed by all listed editors.
Publication of a W3C Note does not imply endorsement by W3C membership. A
list of current W3C technical reports and publications, including working
drafts and notes, can be found at
http://www.w3.org/TR.
NOTE: This document has been modified after its original date of publishing
to correct the "Latest Version" URI.
1. Barriers to Web Access Encountered by People with Disabilities
There are no universally accepted or absolute categorizations of disability.
Terminology related to disabilities varies substantially from country to
country, and also between different disability communities within the same
country. People's abilities vary from person to person for the same type
of disability, and often vary over time as well. This section describes several
general categories of disability and how they relate to Web accessibility.
The term "disability" is used very generally in this document. Many people
with conditions described below would not consider themselves to have
disabilities, however they may have limitations related to sensory, physical
or cognitive functioning which can affect access to the Web and therefore
are described here. They may have experienced changes in several abilities
due to aging. While some of the conditions described may be stable, or
progressive, others are temporary -- for example, repetitive stress injury
due to extensive keyboard use. There is a trend in some communities away
from using medical terminology to describe disability, and a trend in many
communities away from using the negative terminology or epithets frequently
used in the past. This Draft Note does not attempt to comprehensively
address these issues of terminology.
Note that different disabilities sometimes require similar accommodations,
for instance, both an individual who is blind and an individual who cannot
use his or her hands require full keyboard support for commands in browsers
and authoring tools -- one because of inability to visually track the pointer,
and the other because of inability to move the hands. At the same time, many
accessibility solutions contribute to "universal design" by benefiting
non-disabled users as well as disabled users -- support for speech output
not only benefits blind users but also the Web user whose eyes are busy with
another task; while captions of audio not only benefit the deaf user but
also increase the efficiency of searching and indexing audio content on Web
sites.
For each of the barriers described in this section, solutions are available
in W3C's Web Content Accessibility
Guidelines 1.0. A
Checklist
is available to test Web sites for accessibility, and an in-depth
Techniques document
in case any of the solutions recommended in the guidelines are unfamiliar.
Visual Disabilities
-
Blindness
-
Blindness involves a substantial uncorrectable loss of vision in both eyes.
To access the Web, individuals who are blind often rely on screen reading
software, used in conjunction with graphical or text browsers, to drive speech
output or refreshable braille output. Barriers they may encounter on the
Web include:
-
images that do not have alt text
-
complex images such as graphs or charts that do not have extended descriptions
-
video that is not described in text or audio
-
tables that do not make sense when read serially, e.g. in a cell-by-cell
mode
-
frames that do not have "no-frame" alternatives, or that do not have meaningful
names
-
forms that cannot be tabbed through in a logical sequence
-
browsers and authoring tools that do not have keyboard support of all commands
-
Low Vision
-
There are many types of low vision. They include poor acuity (vision that
is not sharp); tunnel vision (seeing only the middle of the visual field);
peripheral vision (seeing only the edges of the visual field); clouded vision;
etc. To use the Web, some people with low vision enlarge fonts and images
slightly or substantially, and many use screen magnifying software to do
this. Some individuals use specific combinations of text and background colors,
for instance, 24-point bright yellow font on a black background, or use certain
kinds of fonts that are clearer for that individual to read. Barriers they
may encounter on the Web include:
-
Web pages with absolute font sizes that do not enlarge easily
-
Web pages that are inconsistently laid out and therefore difficult to navigate
when enlarged due to loss of surrounding context
-
browsers that do not support user override of authors' style sheets
-
Color Blindness
-
Color blindness is a lack of perceptual sensitivity to certain colors. This
may result in difficulty distinguishing between red and green, or between
yellow and blue. Sometimes it may mean an inability to perceive any color.
Barriers that people with color blindness may encounter on the Web include:
-
color that is used as a unique marker to emphasize text on a Web site
-
text that inadequately contrasts with background color or pattern
-
browsers that do not support user override of authors' style sheets
Hearing Disabilities
-
Deafness
-
Deafness involves a substantial uncorrectable impairment of hearing in both
ears. Some deaf individuals' first language is a sign language rather than
a spoken and written language. Barriers that people who are deaf may encounter
on the Web include:
-
lack of captions or transcripts for audio content on the Web
-
lack of visual signposts in pages full of text, which can slow comprehension
for non-native readers of a written language
-
Hard of hearing
-
A person with a mild to moderate hearing impairment may be considered hard
of hearing and may rely on amplification and/or redundant text with audio.
Barriers encountered on the Web include:
-
lack of captions or transcripts for audio content on the Web to support
comprehension of audio tracks
Visual and Hearing Disabilities
-
Deaf-blind
-
If an individual has substantial uncorrectable losses of vision and hearing,
the individual may be considered deaf-blind. Depending on the extent of vision
or hearing losses, requirements with regard to Web access may differ from
those for vision-related disability alone, or those for hearing-related
disability alone. Barriers include:
-
video that is described in audio but not described in text
-
captions that cannot easily be enlarged
Physical Disabilities
-
Mobility
-
Paralysis involves partial or complete loss of muscular control and sensation
in part of the body. Paresis involves slight to extensive weakness in part
of the body. Either condition may be accompanied by pain which can further
impede movement. Individuals with paralysis or paresis may have difficulty
using a regular mouse or keyboard. They may use a specialized mouse; they
may use a keyboard with a layout of keys that matches their range of motion;
they may use a head-mouse, head-pointer, or mouth-stick; voice-recognition
software; an eye-gaze system, or other assistive technologies to access and
interact with the information on Web sites. They may not be able to activate
commands that require multiple keystrokes simultaneously. They may need longer
response times when dealing with interactive forms on Web sites. Barriers
they may encounter include:
-
browsers and authoring tools that do not support serialized keystrokes for
commands
-
forms that cannot be tabbed through in a logical order
-
interactive forms with time-limited response options
-
Dexterity
-
If an individual's muscles are tense and contracted, or if an individual
has problems with coordination or involuntary movements, it may affect their
ability to select keys on the keyboard or targets on a Web page. They may
use similar assistive technologies as individuals with paralysis or paresis;
and may need longer response times for interactive forms. Barriers they may
encounter include:
-
interactive forms with time-limited response options
-
Speech
-
If an individual's vocal chords are affected by a physical disability, he
or she may have difficulty producing speech that is recognizable by some
voice recognition software. As voice recognition is increasingly used in
Web-based applications, an individual with a speech disability may need
alternatives to a voice-based interface. Barriers they encounter may include:
-
Web sites that require voice-based interaction
Cognitive and Neurological Disabilities
-
Learning disabilities
-
Some individuals have difficulty processing written language or images when
read visually, or spoken language when heard, or numbers when read visually
or heard. Some specific learning disabilities can affect ability to focus.
Barriers include:
-
lack of alternative modalities for information on Web sites, for instance
audio in addition to visual, or text or visuals in addition to audio
-
lack of clear and consistent organization of Web sites
-
distracting visual or audio elements
-
Impairments of intelligence
-
Some individuals learn more slowly or have difficulty understanding complex
concepts. Barriers include:
-
lack of clear or consistent organization of Web sites
-
use of overly complex language on Web sites
-
Memory impairments
-
Individuals may have memory difficulties for a variety of reasons: for instance
problems with short-term memory, missing long-term memory, or loss of language.
Barriers include:
-
lack of clear or consistent organization of Web sites
-
use of overly complex language on Web sites
-
Neurological disabilities
-
Some individuals with seizure disorders are triggered by visual flickering
or audio signals at a certain frequency. Avoidance of these visual or audio
frequencies in Web sites prevents inadvertent triggering of seizures. Barriers
include:
-
use of visual or audio frequencies that can trigger seizures
-
Psychiatric disabilities
-
Individuals with mental or emotional disabilities may have difficulty focusing.
Barriers include:
-
lack of clear and consistent organization of a Web sites
-
distracting visual or audio elements
Changes in Ability due to Aging
-
Changes in multiple abilities at the same time
-
Aging can bring multiple changes in abilities which can complicate the process
of making accommodations to a single disability. Examples include impairments
in vision, hearing, memory, or dexterity, any of which can affect an individual's
ability to access Web content, however together these conditions can be more
complex to accommodate. For example, someone with low vision may need screen
magnification, however one loses some surrounding contextual information
when using screen magnification, which may further hinder an individual who
also has limited short-term memory. Barriers can include any of the issues
already mentioned above.
The following is a list of assistive technologies that some people with
disabilities use to browse the Web. Assistive technologies are products used
by people with disabilities to help accomplish tasks that they cannot accomplish
otherwise or could not do easily otherwise. When dealing with the Web, assistive
technologies usually refer to adaptive software, specially designed hardware
devices, and/or standard devices used in alternative ways to provide access
for people with disabilities.
Some assistive technologies rely on output of other user agents, such as
graphical desktop browsers, text browsers, voice browsers, multimedia players,
plug-ins.
-
Alternate keyboards or switches
-
Hardware or software devices, used by people with physical disabilities,
that provide an alternate way of creating keystrokes that appear to come
from the standard keyboard. Examples include on-screen keyboards, eyegaze
keyboards, and sip-and-puff switches. Applications that can be operated entirely
from the standard keyboard , with no mouse movements required, support
single-switch access or access via alternative keyboards.
-
Braille and refreshable braille
-
Braille is a technique involving six to eight dots that are raised in different
patterns to represent letters and numbers so that they may be read by people
who are blind using their fingertips. Braille systems vary greatly around
the world. Some "grades" of braille include additional codes beyond standard
alpha-numeric characters, to represent common letter groupings (e.g., "th,"
"ble" in Grade II American English braille) to make braille more compact.
An 8-dot version of braille has been developed to allow all ASCII characters
to be represented. Dynamic or refreshable braille involves the use of a
mechanical display where dots can be raised and lowered dynamically to allow
any braille words to be displayed. Only letters and numbers can be represented
in braille, although some braille printers have a utility that allows simple
graphics to be drawn on a sheet using the raised dots at a resolution of
approximately 11 dots per inch.
-
Screen magnifiers
-
Software used primarily by individuals with low vision that magnifies a portion
of the screen for easier viewing. Note that at the same time screen magnifiers
make presentations larger, they also reduce the area of the document that
may be viewed. Some screen magnifiers therefore offer two views of the screen:
one magnified and one default size for navigation.
-
Screen readers:
-
Software used by individuals who are blind or have learning disabilities
that interprets what is displayed on a screen, and directs it either to speech
synthesis, for audio output, or refreshable braille, for tactile output.
Some screen readers use the document tree (i.e., the parsed document) as
their input. However, older screen readers make use of the rendered version
of a document, meaning that document order or structure may be lost (e.g.,
when tables are used for layout) and their output may be confusing.
-
Sound notification
-
Features of some operating systems that allow deaf or hard of hearing users
to receive visual notification that a warning or error sound has been emitted
by the computer.
-
Scanning software
-
Software used by individuals with some physical or cognitive disabilities
that highlights or announces selection choices (e.g., menu items, groups
of possible phrases, etc.) one at a time. A user selects a desired item by
hitting a switch when the desired item is highlighted or announced.
-
Voice recognition
-
Voice recognition is used by people with some physical disabilities or temporary
injuries to hands and forearms -- as well as some users interested in greater
convenience, and as an input method in some voice browsers. Applications
that have full keyboard support can be used with voice recognition.
Examples of Accessibility and Inaccessibility on the Web
[Adapt Marja's "scenarios" here]
About the Web Accessibility Initiative
[Edit/update based on CSS boilerplate]
W3C's Web Accessibility Initiative (WAI) addresses accessibility of the Web
through five complementary activities that:
-
Ensure that the technology of the Web supports accessibility
-
Develop accessibility guidelines
-
Develop tools to facilitate evaluation and repair of Web sites
-
Conduct education and outreach
-
Conduct research and development
WAI's International Program Office enables partnering of industry, disability
organizations, accessibility research organizations, and governments interested
in creating an accessible Web. WAI sponsors include the US National Science
Foundation and Department of Education's National Institute on Disability
and Rehabilitation Research; the European Commission's DG XIII Telematics
for Disabled and Elderly Programme; IBM, Lotus Development Corporation, and
NCR.
Additional information on WAI is available at
http://www.w3.org/WAI.
[Edit/update]
Web accessibility guidelines are essential for Web site development and for
Web-related applications development. WAI is coordinating with many organizations
to produce three sets of guidelines:
-
"Web Content Accessibility
Guidelines", W. Chisholm, G. Vanderheiden, and I. Jacobs, eds. These
guidelines explain how to design accessible Web content.
-
"Authoring Tool Accessibility
Guidelines", J. Treviranus, J. Richards, I. Jacobs, C. McCathieNevile,
eds. These guidelines explain how to build accessible Web authoring tools.
-
"User Agent Accessibility
Guidelines", J. Gunderson and I. Jacobs, eds. These guidelines explain
how to design accessible user agents (browsers, multimedia tools, assistive
technologies, etc.)
About the World Wide Web Consortium (W3C)
The W3C was created to lead the Web to its full potential by developing common
protocols that promote its evolution and ensure its interoperability. It
is an international industry consortium jointly run by the MIT Laboratory
for Computer Science (LCS) in the USA, the National Institute for Research
in Computer Science and Control (INRIA) in France and Keio University in
Japan. Services provided by the Consortium include: a repository of information
about the World Wide Web for developers and users; reference code implementations
to embody and promote standards; and various prototype and sample applications
to demonstrate use of new technology. To date, more than 320 organizations
are Members of the Consortium. For more information about the World Wide
Web Consortium, see http://www.w3.org/
Contributors
Gregg Vanderheiden, Kate Vanderheiden, [add EOWG once reviewed, other WAI
groups once reviewed]
References
[Select a few key & stable references]