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 disabilities and those with functional limitations, for the purpose
of better understanding functional requirements and technical issues involved
in ensuring an accessible Web.
Specifically, this document describes functional requirements relevant to
Web access for various kinds of disabilities; describes some of the assistive
technologies used by people with disabilities when accessing the Web; and
provides examples of how people with disabilities might successfully or
unsuccessfully use Web sites or applications based on accessible implementations
of features supporting accessibility.
This document is not intended as a comprehensive or in-depth description
of disabilities, nor of assistive technologies used by people with disabilities.
Additional information on these topics is available on the Web.
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 three
WAI guidelines working groups, 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. Functional Requirements Related to Disabilities and the Web
The following discussion provides examples of Web-related functional requirements
for various disabilities and functional limitations. For purposes of
organization, we have grouped types of disabilities into several categories
with similar functional requirements for Web accessibility. Note that different
functional requirements are sometimes shared by different types of disabilities;
for instance, both an individual who is blind and an individual who cannot
use his or her hands require full keyboard redundancy for mouse commands
in Web-based applications -- one because of difficulty with hand-eye coordination
due to inability to visually track the pointer, and the other because of
inability to move the hands. Similarly, clear and consistent organization
of Web sites benefits many kinds of disabilities; for example, people with
cognitive disabilities, people using voice recognition due to physical
disability, and people using voice browsers due to blindness. The reader
may note that each of these "accessibility solutions" also benefits non-disabled
users: keyboard redundancy for mouse commands can speed access for "power
users," while clear and consistent organization of Web sites appears to benefit
the majority of Web users.
Terminology related to disabilities varies substantially from country to
country, and also between different disability communities within the same
country. 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 functional limitations related to sensory,
physical or cognitive functioning which can affect access to the Web and
therefore are addressed here. While some of the conditions described may
be stable, or progressive, others are temporary -- for example, repetitive
stress injury of the forearms due to extensive keyboard use. There is a trend
in some communities away from medical terminology to describe disability,
and a trend in many comunities away from negative terminology or epithets
for disabilities which were frequently used in the past. This Draft
Note does not attempt to comprehensively address these issues of terminology.
Sometimes the aging process brings certain changes in abilities for individuals
who do not consider themselves to have disabilities. These changes may involve
slight or substantial changes in several types of functioning at once, for
instance, changes in vision and hearing, coupled with short-term memory issues
and/or loss of dexterity. These kinds of changes can result in difficulty
using the Web, and this Draft Note includes these issues in its
consideration of functional requirements.
Vision
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Blindness
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In some countries, people are considered "legally blind" when they have less
than 20/200 vision in the better eye after correction, or less than a 20
degree field of view in the better eye after correction. Individuals who
are blind may rely on screen reading software, with speech or braille output,
used in conjunction with graphical or text browsers to access the Web, or
they may rely on voice browsers. For graphics, they may rely on the presence
of a text description to understand the content or function of the image;
for video, they rely on a text or audio description of the movement in the
video. Screen reading software may or may not be able to read the mark-up
on tables and frames unless they are marked up appropriately or have alternative
content available. Individuals who are blind may be unable to use a mouse
to navigate through a complex form or to activate commands in a Web browser,
and so may require keyboard support of all mouse commands.
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Low Vision
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There are many types of low vision, including poor acuity, "tunnel" vision,
clouded vision, "floaters" in the eye, peripheral vision only, etc. Some
people with low vision need to enlarge fonts and images slightly or
substantially, and may use screen magnifying software to do this. Some
individuals need to use specific combinations of text and background colors,
for example a 24-point yellow font on a black background, or to use specific
fonts that are clearer for that individual to read. Web pages that use relative
font sizes instead of absolute font sizes will enlarge more evently. Use
of style sheets on Web pages, and support for user override of author style
sheets in browsers, can enable an individual to view a page with their optimum
font choice. Web pages present more navigational challenges when enlarged,
due to loss of contextual information when a user cannot see information
or choices outside of the magnified area, therefore appropriate use of structural
mark-up and clear and consistent page layout can facilitate navigation.
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Color Blindness
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"Color blindness" is a lack of perceptual sensitivity to certain colors.
This may result in a difficulty distinguishing between red and green, or
between yellow and blue. Sometimes it may mean an inability to perceive any
color. Individuals with color blindness may be unable to perceive color that
is used as a unique marker to emphasize text on a Web site, or be unable
to perceive text that inadequately contrasts with background color. Author
choice of adequately contrasting colors, and use of style sheets and browsers
supporting user override of author style sheets, can ensure access to Web
content.
Hearing
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Deafness
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In some countries a person is considered deaf when sound must reach at least
90 decibels to be heard at all, and even amplified speech cannot be understood.
Spoken conversation is approximately 40 to 60 decibels. Individuals who are
deaf rely on captioning or transcription of speech and sounds to access the
content of Web-based audio.
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Hard of hearing
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A person with a mild to moderate hearing impairment may be considered hard
of hearing. Captioning or transcription of Web-based audio can provide additional
support for what an individual who is hard-of-hearing can understand from
the audio.
Vision and Hearing
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Deaf-blind
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If an individual has a substantial vision and hearing loss, the individual
may be considered deaf-blind. Depending of the extent of the vision or hearing
loss, the functional requirements with regard to Web access may differ from
those for vision-related disability alone, or those for hearing-related
disability alone. For example, an individual who is very hard of hearing
in addition to being blind would not benefit from an audio description of
Web-based video, but may be able to access a text description of the video
through refreshable braille output. An individual who is deaf, has very limited
vision, and does not read braille, might access the content of Web-based
audio through reading captions that are greatly enlarged.
Mobility and Dexterity
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Paralysis and paresis
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Paralysis involves partial or complete loss of muscular control and often
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 mouse or keyboard. They may need to use a mouse which
requires less effort to move or can be held in a certain position; they may
use a keyboard with a layout of keys that matches their range of motion;
they may use a head-mouse, mouth-stick or head-pointer, voice-recognition
software, an eye-gaze system, or any one of a number of other assistive
technologies to access and interact with the information on Web sites. They
may need longer response times when dealing with interactive forms on Web
sites.
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Interference with Control
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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.
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Speech disabilities
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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; for instance, information available
via voice interaction over the phone would also need to be available via
a Web site that can be accessed through a keyboard.
Cognition and Neurological Function
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Specific learning disabilities
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Some individuals have difficulty processing written language when read visually,
or spoken language when heard, or numbers when read visually or heard. Some
specific learning disabilities or psychiatric disabilities can affect ability
to focus. Access to the content of a Web page in a redundant modality (audio
in addition to visual, or text or visuals in addition to audio) can support
comprehension. Clear and consistent organization of a Web site can minimize
distractions and facilitate focus.
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Memory impairments
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Individuals may have memory difficulties for a variety of reasons: problems
with short-term memory, missing long-term memory, loss of language. Clear
and consistent organization of a Web site and use of clear language can
facilitate comprehension and navigation through a Web site.
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Impairments of intelligence or thinking
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Some individuals learn more slowly or have difficulty understanding complex
concepts. Clear and consistent organization of Web sites, together with language
that is not unnecessarily complex for the content, can facilitate comprehension.
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Neurological disabilities
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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.
Changes in Ability due to Aging
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Gradual changes in function
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Aging can bring an increased incidence of functional limitations, some of
which arise gradually ,and for which the individual may therefore be less
likely to seek or become familiar with compensating strategies. Examples
include decreases in vision, hearing, memory, or dexterity, any of which
can affect an individual's ability to access Web content.
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Multiple functional changes
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Aging can bring combinations of functional changes which can complicate
accommodations to a single disability. For example, someone with low vision
may need screen magnification, however one loses some surrounding contextual
information when using screen magnification, and that may further slow down
or confuse an individual who also has limited short-term memory.
The following is a list of assistive technologies that some people with
disabilities use to browse the Web. Assistive technologies are products used
to help people accomplish tasks that they cannot accomplish otherwise. When
dealing with the Web, assistive technologies usually refer to software
adaptations, specially designed hardware devices, and/or standard devices
used in alternative ways which provide user access.
Some "dependent" assistive technologies rely on output of other "user agents"
for their input. User agents include graphical desktop browsers, text browsers,
voice browsers, multimedia players, plug-ins, as well as these dependent
assistive technologies.
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Alternate keyboards or switches
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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.
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Braille and refreshable braille
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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. Note. The word "braille"
should only be capitalized when referring to Louis Braille, inventor of the
system.
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Screen magnifiers
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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.
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Screen readers:
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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.
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Sound notification
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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.
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Scanning software
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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.
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Voice recognition
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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:
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Ensure that the technology of the Web supports accessibility
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Develop accessibility guidelines
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Develop tools to facilitate evaluation and repair of Web sites
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Conduct education and outreach
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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:
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"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]