Wendy Chisholm,
Trace R & D Center,
University of Wisconsin -- Madison
Gregg Vanderheiden,
Trace R & D Center,
University of Wisconsin -- Madison
Ian Jacobs, W3C
This document is a NOTE made available by the W3C for discussion
only. Publication of this Note by W3C indicates no endorsement by W3C
or the W3C Team, or any W3C Members.
While Web Content Accessibility Guidelines 1.0 strives to be a stable document (as a W3C
Recommendation), the current document is expected to evolve as
technologies change and content developers discover more effective
techniques for designing accessible pages.
A Web content developer must satisfy this
checkpoint. Otherwise, one or more groups will find it impossible to
access information in the document. Satisfying this checkpoint is a
basic requirement for some groups to be able to use Web documents.
A Web content developer should satisfy this
checkpoint. Otherwise, one or more groups will find it difficult to
access information in the document. Satisfying this checkpoint will
remove significant barriers to accessing Web documents.
A Web content developer may
address this checkpoint. Otherwise,
one or more groups will find it somewhat difficult to access
information in the document. Satisfying this checkpoint will improve
access to Web documents.
Some checkpoints specify a priority level that may change under
certain (indicated) conditions.
The checkpoints in this document are numbered to match their
numbering in Web Content Accessibility Guidelines 1.0.
This document is a list of techniques that implement the
checkpoints defined in "Web Content Accessibility Guidelines 1.0". This document is organized
as follows:
This section explains how to implement applicable
checkpoints in HTML (refer to
[HTML40],
[HTML32])
and includes numerous practical examples.
To complement this section, an
index of HTML elements and attributes
provides information about
all elements of HTML 4.0 and all attributes that affect
accessibility directly. For each element, the index
includes links to techniques that refer to it.
This section explains how to implement applicable
checkpoints in CSS1 and CSS2 (refer to [CSS1],
[CSS2]).
A checkpoint map has been provided
for navigation of the techniques. For each checkpoint, the map
includes its definition (as it appears in the "Web Content Accessibility Guidelines 1.0") and links
to applicable techniques for the checkpoint. In addition,
the beginning of each section of this document lists the checkpoints
that are addressed in that section.
This document contains a number of examples that illustrate
accessible solutions in HTML, CSS, etc. but also deprecated examples
that illustrate what content developers should not do. The deprecated
examples are highlighted and readers should approach them with caution
-- they are meant for illustrative purposes only.
When designing a document or series of documents, content developers
should strive first to identify the desired structure for their documents
before thinking about how the documents will be presented to the
user. Distinguishing the structure of a document from how the
content is presented offers a number of advantages, including
improved accessibility, manageability, and portability.
Identifying what is structure and what is presentation may be
challenging at times. For instance, many content developers consider that a horizontal
rule (the HR element) communicates a structural division. This may
be true for sighted users, but to unsighted users or users without
graphical browsers, a horizontal rule has next to no meaning (One might "guess" that
an HR element implies a structural division, but
without other information, there is no guarantee.) In HTML, content developers
should
use the HTML 4.0 header elements (H1-H6) to identify new sections.
These may be complemented by visual or other cues such as
horizontal rules, but should not be replaced by them.
The inverse holds as well: content developers should not use structural
elements to achieve presentation effects. For instance in HTML, even though
the BLOCKQUOTE element may cause indented
text in some browsers, it is designed to identify a quotation,
not create a presentation side-effect.
BLOCKQUOTE elements used for indentation confuse users and search
robots alike, who expect the element to be used to mark up block
quotations.
The separation of presentation from structure in
XML documents
is inherent. As Norman Walsh states in "A Guide to XML"
[WALSH],
HTML browsers are
largely hardcoded. A first level heading appears the way it does because
the browser recognizes the H1
tag. Again, since XML documents have no
fixed tag set, this approach will not work. The presentation of an XML
document is dependent on a stylesheet.
Quicktest! To determine if content is
structural or presentational, create an outline of your document. Each point
in the hierarchy denotes a structural change. Use structural markup to
mark these changes and presentational markup to make them more
apparent visually and aurally. Notice that horizontal rules will not
appear in this outline and therefore are not structural, but presentational.
Note. This quicktest addresses chapter, section,
and paragraph structure. To determine structure within phrases, look for
abbreviations, changes in natural language, definitions, and list items.
Text is considered accessible to almost all users since it may
be handled by screen readers, non-visual browsers, and braille readers.
It may be displayed visually, magnified, synchronized with a video to create a caption,
etc. As you design a document containing
non-textual information (images, applets, sounds, multimedia
presentations, etc.),
think about supplementing that information with textual
equivalents wherever possible.
A text equivalent describes the function or purpose of content.
For complex content (charts, graphs, etc.), the text equivalent
may be longer and include descriptive information.
Text equivalents should be provided for logos, photos, submit
buttons, applets, bullets in lists, ascii art,
and all of the links within an
image map as well as invisible images used to lay out a page.
Quicktest! A good test to
determine if a text equivalent is useful is to imagine reading the
document aloud over the telephone. What would you say upon
encountering this image to make the page comprehensible to the
listener?
How one specifies a text equivalent depends on the
document language.
For example, depending on the element, HTML allows content
developers to specify text equivalents through attributes ("alt" or "longdesc" )
or in element content (the OBJECT element).
Video formats, such as Quicktime, will allow developers to include
a variety of alternative audio and video tracks. SMIL ([SMIL]), allows developers
to synchronize alternative audio and video clips, and text files with each
other.
In creating XML DTDs, ensure that elements that might need a
description have some way of associating themselves with the
description.
Some image formats allow internal text in the data file along with
the image information. If an image format supports such text (e.g.,
Portable Network Graphics, see [PNG]) content
developers may also supply information there as well.
Content developers must consider backward compatibility
when designing Web pages or sites since:
Some user agents do not support some HTML features,
People may use older browsers or video players,
Compatibility problems may arise between software
Therefore, when designing for older technologies,
consider these techniques:
Provide inline text equivalents. For example, include a
description of the image immediately after the image.
Provide links to long text equivalents either in
a different file or on the same page. These
are called description links or
"d-links". The link text should explain that the link designates
a description. Where possible, it should also explain
the nature of the description.
However, content developers concerned about how the description link will
affect the visual appearance of the page may use more discrete link
text such as "[D]", which is recommended by NCAM (refer to [NCAM]). In this case, they should also provide
more information about the link target so that users can distinguish
links that share "[D]" as content (e.g., with the "title" attribute in HTML).
Although it is possible to make most content accessible,
it may happen that all or part of a page remains inaccessible.
Additional techniques for creating accessible
alternatives include:
Provide a phone number, fax number, e-mail, or postal
address where information is available and accessible, preferably
24 hours a day
Here are two techniques for linking to an accessible
alternative page:
Provide links at the top of both the main and alternative pages
to allow a user to move back and forth between them.
For example,
at the top of a graphical page include a link to the text-only page,
and at the top of a text-only page include a link to the associated
graphical page. Ensure that these links are one of the first that
users will tab to by placing them at the top of the page, before other
links.
Use meta information to designate alternative documents. Browsers should
load the alternative page automatically based on the user's
browser type and preferences. For example, in
HTML, use the LINK element as follows:
Example.
User agents that support LINK will load the alternative page for
those users whose browsers may be identified as supporting "aural","braille", or "tty" rendering.
Not every user has a graphic environment with a mouse or other
pointing device. Some users rely on keyboard, alternative keyboard
or voice input to
navigate links, activate form controls, etc. Content
developers should always
ensure that users may interact with a page with devices other than
a pointing device. A page designed for keyboard access (in addition
to mouse access) will generally be accessible to users with other
input devices. What's more, designing a page for keyboard access
will usually improve its overall design as well.
Keyboard access to links and form controls may be specified in
a few ways:
Provide keyboard shortcuts so that users may combine keystrokes to
navigate links or form controls on a page.
Note.
Keyboard shortcuts -- notably the key used to
activate the shortcut -- may be handled differently by different
operating systems. On Windows machines, the "alt" and "ctrl"
key are most commonly used while on a Macintosh, it is the apple or "clover
leaf" key. Refer to the Keyboard access for links
and Keyboard Access to Forms
sections for examples.
Tabbing order
Tabbing order describes a (logical) order for navigating from
link to link or form control to form control (usually by pressing
the "tab" key, hence the name). Refer to the
Keyboard Access to Forms
section for examples.
Some elements import objects (e.g., applets
or multimedia players) whose interfaces cannot
be controlled through the markup language. In such cases,
content developers should provide
alternative equivalents with accessible interfaces
if the imported objects themselves do not provide
accessible interfaces.
A consistent style of presentation on each page allows users to
locate navigation mechanisms more easily but also to skip
navigation mechanisms more easily to find important content.
This helps people with learning and reading disabilities but
also makes navigation easier for all users. Predictability
will increase the likelihood that people will find
information at your site, or avoid it when they so desire.
Examples of structures that may appear at the same place between pages:
navigation bars
the primary content of a page
advertising
A navigation mechanism creates a set of paths a user may take
through your site. Providing navigation bars, site maps,
and search features all increase the likelihood that a user will
reach the information they seek at your site. If your site is
highly visual in nature, the structure might be harder to navigate
if the user can't form a mental map of where they are going or
where they have been. To help them,
content developers should describe any navigation mechanisms.
It is crucial that the descriptions and site guides be
accessible since people who are lost at your site will rely
heavily on them.
When providing search functionality, content developers should
offer search mechanisms that satisfy varying skill levels and
preferences. Most search facilities require the user to enter
keywords for search terms. Users with spelling disabilities and users
unfamiliar with the language of your site will have a difficult time
finding what they need if the search requires perfect spelling.
Search engines might include a spell checker, offer "best
guess" alternatives, query-by-example searches, similarity searches,
etc.
The following writing style suggestions should help make the
content of your site easier to read for everyone, especially people
with reading and/or cognitive disabilities. Several guides (including
[HACKER]) discuss these and other writing
style issues in more detail.
Strive for clear and accurate headings and link descriptions.
This includes using link phrases that are terse and that
make sense when
read out of context or as part of a series of links (Some users
browse by jumping from link to link and listening only to link text.)
Use informative headers so that users can
scan a page quickly for information rather than reading it in detail.
State the topic of the sentence or paragraph at the beginning of the
sentence or paragraph (this is called "front-loading").
This will help both people who are skimming
visually, but also people who use speech synthesizers.
"Skimming" with speech currently means that the user jumps from
heading to heading, or paragraph to paragraph and listens to just enough
words to determine whether the current chunk of information (heading,
paragraph, link, etc.) interests them. If the main
idea of the paragraph is in the middle or at the end, speech users may have
to listen to most of the document before finding what they want.
Depending on what the user is looking for and how much they know about
the topic, search features may also help users locate content more
quickly.
Limit each paragraph to one main idea.
Avoid slang, jargon, and specialized meanings of familiar words,
unless defined within your document.
Favor words that are commonly used. For example, use "begin"
rather than "commence" or use "try" rather
than "endeavor."
Use active rather than passive verbs.
Avoid complex sentence structures.
To help determine whether your document is easy to read, consider
using the Gunning-Fog reading measure (described in [SPOOL] with examples and the algorithm online
at [TECHHEAD]). This algorithm generally
produces a lower score when content is easier to read. As example
results, the Bible, Shakespeare, Mark Twain, and TV Guide all have Fog
indexes of about 6. Time, Newsweek, and the Wall St. Journal an
average Fog index of about 11.
For people who do not read well or not at all,
multimedia (non-text) equivalents
may help facilitate comprehension. Beware that
multimedia presentations do not always make text easier to understand.
Sometimes, multimedia presentations may make it more confusing.
Examples of multimedia that supplement text:
A chart of complex data, such as sales figures of a business for the past fiscal year.
A translation of the text into a Sign Language movie clip. Sign
Language is a very different language than spoken languages.
For example, some people who may communicate via American Sign Language
may not be able to read American English.
Pre-recorded audio of music, spoken language, or sound
effects may also help non-readers who can perceive audio presentations.
Although text may be generated as speech through speech synthesis, changes in
a recorded speaker's voice can convey information that is lost through synthesis.
Instead of including links such as "Here is the
French version of this document", use content negotiation
so that the French version is served to clients requesting
French versions of documents.
If not possible to use content negotiation, indicate content type
or language through markup (e.g., in HTML use "type" and "hreflang").
Content developers sometimes create pages that
refresh or change without
the user requesting the refresh. This automatic refresh
can be very disorienting to some users. Instead, in order of preference,
authors should:
Configure the server to use
the appropriate HTTP status code (301).
Using HTTP headers is preferable because
it reduces Internet traffic and download times, it may by
applied to non-HTML documents, and it may be used by agents who
requested only a HEAD request (e.g., link checkers).
Also, status codes of the 30x type provide
information such as "moved permanently" or "moved temporarily"
that cannot be given with META refresh.
Replace the page that would be redirected with a static
page containing a normal link to the new page.
Note. Both checkpoint 7.4 and
checkpoint 7.5 address problems posed by legacy user
agents. Newer user agents should disable refresh and substitute a link
to new information at the top of the page.
The following are deprecated HTML examples. The
first changes the user's page at page at regular intervals. Content
developers should not use this technique to simulate
"push" technology. Developers cannot predict how much time a user
will require to read a page; premature refresh can disorient
users. Content developers should avoid periodic refresh and allow
users to choose when they want the latest information.
Deprecated example.
...Information...
The following HTML example (using the META element) forwards the user from one page to
another after a timeout. However, users should
not redirect users with this markup since is
non-standard, it disorients users, and it can disrupt a browser's
history of visited pages.
Deprecated example.
Don't use this!
If your browser supports Refresh,
you'll be transported to our
new site
in 5 seconds, otherwise, select the link manually.
A flickering or flashing screen may cause seizures in users with
photosensitive epilepsy and content developers should thus avoid
causing the screen to flicker. Seizures can be triggered by flickering
or flashing in the 4 to 59 flashes per second (Hertz) range with a
peak sensitivity at 20 flashes per second as well as quick changes
from dark to light (like strobe lights).
This section discusses strategies and techniques for testing Web
documents to determine accessibility issues that have been resolved
and those that haven't. These tests should highlight major access
issues, are valuable in reducing a number of accessibility
barriers. However, some of these testing scenarios only replicate
conditions caused by a disability; they do not simulate the full
experience a user with a disability might have. In real-life
settings, your pages may be less usable than you expected. Thus, one
of the strategies recommends that content developers observe people
with different disabilities as they attempt to use a page or site.
If, after completing the following tests and adjusting your design
accordingly, you find that a page is still not accessible, it is
likely that you should create an alternative
page that is accessible.
Note. Passing these tests does not guarantee conformance to the
"Web Content Accessibility Guidelines 1.0".
A validator can verify the syntax of your pages (e.g., HTML, CSS,
XML). Correct syntax will help eliminate a number of accessibility
problems since software can process well-formed documents more
easily. Also, some validators can warn you of some accessibility
problems based on syntax alone (e.g., a document is missing an
attribute or property that is important to accessibility). Note,
however, that correct syntax does not guarantee that a document will
be accessible. For instance, you may provide a text equivalent for an
image according to the language's specification, but the text may be
inaccurate or insufficient. Some validators will therefore ask you
questions and step you through more subjective parts of the
analysis. Some examples of automatic validators include:
Validators usually report what issues to solve and often give examples of
how to solve them. They do not usually help an author walk through
each problem and help the author modify the document
interactively. The
WAI Evaluation and Repair Working Group ([WAI-ER])
is working to develop a suite of
tools that will help authors not only identify issues but solve them
interactively.
Keep in mind that most user agents (browsers) and operating systems allow
users to configure settings that change the way software looks, sounds, and
behaves. With the variety of user agents, different users will have
very different experiences with the Web. Therefore:
frames, scripts, style sheets, and applets not loaded.
Use several browsers, old and new.Note. Some operating systems or browsers
do not allow multiple installations of the browser
on the same machine. It may also be difficult to
locate older browser software.
Use other tools
such as a self-voicing browser (e.g.,
[PWWEBSPEAK] and
[HOMEPAGEREADER]),
a screen reader (e.g.,
[JAWS] and
[WINVISION]),
magnification software, a small display,
an onscreen keyboard, an alternative keyboard, etc.
A person reading a page with a speech
synthesizer may not be able to decipher the synthesizer's best guess
for a word with a spelling error. Grammar checkers will help to ensure
that the textual content of your page is correct. This will help
readers for whom your document is not written in their native tongue, or
people who are just learning the language of the document. Thus, you will
help increase the comprehension of your page.
Note.At the time of this writing, not all
user agents support some of the (new) HTML 4.0 attributes and elements
that may significantly increase accessibility of Web pages.
Please refer to the W3C Web site ([WAI-UA-SUPPORT]) for information about
browser and other user agent support of accessibility features.
In general, please note that HTML user agents ignore attributes
they don't support and they render the content of unsupported
elements.
The following sections list some techniques for designing
accessible HTML documents. The sections are organized by topic (and
mirror the organization of the HTML 4.0 specification, [HTML40]).
Content developers should use structural markup and use it
according to specification. Structural elements and attribute (refer
to the index of HTML elements and attributes
to identify them) promote consistency in documents and supply
information to other tools (e.g., indexing tools, search engines,
programs that extract tables to databases, navigation tools that use
header elements, and automatic translation software that translates
text from one language into another.
Some structural elements provide information about the document
itself. This is called "metadata" about the document -- Metadata is
information about data. Well-crafted metadata can provide
important orientation information to users. HTML elements that
provide useful information about a document include:
TITLE: The document title. Note that
the (mandatory) TITLE element, which only appears once in a document,
is different from the "title" attribute,
which applies to almost every HTML 4.0 element.
Content developers should use the "title" attribute
in accordance with the HTML 4.0 specification. For example,
"title" should be used with links to provide information
about the target of the link.
ADDRESS: Can be used to provide information about the creator of
the page.
LINK: Can be used to indicate alternative documents (different
structure, different language, different target device, etc.).
The META element can specify
arbitrary metadata for a document.
Please refer to the section on
automatic page refresh for information on why META
should not be used to redirect pages.
Sections should be introduced with the HTML header elements
(H1-H6). Other markup may complement these elements to improve
presentation (e.g., the HR
element to create a horizontal dividing
line), but visual presentation is not sufficient to identify
document sections.
Since some users skim
through a document by navigating its headings, it is important to
use them appropriately to convey document structure. Users should
order heading elements properly. For example,
in HTML, H2 elements should follow H1 elements, H3 elements should
follow H2 elements, etc. Content developers should not "skip" levels (e.g.,
H1 directly to H3). Do not use headings to create font effects;
use style sheets to change font styles
for example.
Note that in HTML, heading elements (H1 - H6) only start sections,
they don't contain them as element content. The following HTML markup
shows how style sheets may be used to control the appearance
of a header and the content that follows:
Content developers should use the LINK
element and link types (refer to [HTML40],
section 6.12) to describe document navigation mechanisms
and organization. Some user agents may synthesize
navigation tools or allow ordered printing of a set of documents based
on such markup.
Use section headers (H1 - H6)
to create structured documents and break up long stretches of text.
Break up lines of text into paragraphs (with the P element).
All of these grouping mechanisms should be used when appropriate
and natural, i.e., when the information lends itself to logical
groups. Content developers should not create groups randomly, as
this will confuse all users.
And with a certain je ne sais quoi,
she entered both the room, and his life, forever. My name
is Natasha, she said. Piacere,
he replied in impeccable Italian, locking the door.
End example.
Identifying changes in language are important for a number of reasons:
Users who are reading the document in braille will be able to substitute
the appropriate control codes (markup) where language changes occur to ensure
that the braille translation software will generate the correct characters
(accented characters, for instance). These control codes also prevent braille
contractions from being generated, which could further confuse the user.
Braille contractions combine commonly used groups of characters that usually
appear in multiple cells into a single cell. For example, "ing" which usually
takes up three cells (one for each character) can be contracted into a single
cell.
Similarly, speech synthesizers that "speak" multiple languages will be
able to generate the text in the appropriate accent with proper pronunciation.
If changes are not marked, the synthesizer will try its best to speak the words
in the primary language it works in. Thus, the French word for car,
"voiture"
would be pronounced "voter."
Users who are unable to translate between languages themselves, will
be able to have unfamiliar languages translated by machine translators.
It is also good practice to identify the primary language of a
document, either with markup (as shown below) or through HTTP
headers.
The proper HTML elements should be used to mark up emphasis: EM and STRONG. The
B and I elements
should not be used; they are used to create a visual presentation
effect. The EM and STRONG elements were designed to indicate
structural emphasis that may be rendered in a variety of ways (font
style changes, speech inflection changes, etc.)
Using markup (and style sheets) where possible rather than images
(e.g., a mathematical equation) promotes accessibility for the
following reasons:
Text may be magnified or interpreted as speech or
braille.
Search engines can use text information.
As an example, consider these techniques for putting
mathematics on the Web:
Ensure that users know what variables represent, for example,
in the equation "F = m * a", indicate
that F= Force, m = mass, a = acceleration.
For straightforward equations, use characters, as in
"x + y = z"
For more complex equations, mark them up
with MathML ([MATHML]) or
TeX. Note. MathML can be used to create very accessible
documents but currently is not as widely supported or used as TeX.
Provide a text description of the equation and, where possible,
use character entity references to create the mathematical symbols.
A text equivalent must be provided
if the equation is represented by one or more images.
TeX is commonly used to create technical papers which are then
converted to HTML for publication on the Web. However, converters
tend to generate images, use deprecated markup, and use tables
for layout. Consequently, content providers should:
Make the original TeX (or LaTeX) document available on
the Web. There is a system called "AsTeR"
([ASTER]) that can create an
auditory rendition of TeX and LaTeX documents.
Also, IBM has a plug-in for Netscape and Internet Explorer
that reads TeX/LaTeX documents and some of MathML (refer
to [HYPERMEDIA]).
Ensure that the HTML created by the conversion
process is accessible. Provide a single description
of the equation (rather than "alt" text on every generated
image as there may be small images for bits and pieces of the
equation).
The HTML list elements DL,
UL, and OL
should only be used to create lists, not for
formatting effects such as indentation.
Ordered lists help non-visual users navigate.
Non-visual users may "get lost" in lists, especially in nested lists
and those that do not indicate the specific nest level for each
list item. Until user agents provide a means to identify list context
clearly (e.g., by supporting the ':before' pseudo-element in CSS2),
content developers should include contextual clues in their lists.
For numbered lists, compound numbers are more informative than
simple numbers. Thus, a list numbered "1, 1.1, 1.2, 1.2.1, 1.3, 2,
2.1," provides more context than the same list without
compound numbers, which might be formatted as follows:
1.
1.
2.
1.
3.
2.
1.
and would be spoken as "1, 1, 2, 1, 2, 3, 2, 1", conveying
no information about list depth.
[CSS1] and [CSS2]
allow users to control number styles (for all list, not just ordered)
through user style sheets.
Example.
The following CSS2 style sheet shows how to specify compound numbers
for nested lists created with either UL or OL elements.
Items are numbered as "1", "1.1", "1.1.1", etc.
End example.
Until either CSS2 is widely supported or user
agents allow users to control rendering of lists through other means,
authors should consider providing contextual clues in unnumbered
nested lists. Non-visual users may have difficulties knowing where a
list begins and ends and where each list item starts. For example, if
a list entry wraps to the next line on the screen, it may appear to be
two separate items in the list. This may pose a problem for legacy
screen readers.
To change the "bullet" style of unordered list items
created with the LI element, use style
sheets. In CSS, it is possible to specify a fallback bullet
style (e.g., 'disc') if a bullet image cannot be loaded.
Example.
Using style sheets to change bullets
Audrey
Laurie
Alice
End example.
To further ensure that users understand differences between list
items indicated visually, content developers should provide a text label
before or after the list item phrase:
Example.
In this example, new information is communicated through text
("New"), font style (bold), and color (yellow bullet, red text on
yellow background).
Bullet styles example
Roth IRA New
401(k)
End example.
Avoid using images as bullets in definition lists created with
DL, DT, and
DD. However, if this method is used, be
sure to provide a text equivalent for
the images.
Deprecated example.
Deprecated example using image in DL lists
Audrey
Laurie
Alice
Content developers should avoid list styles where bullets provide
additional (visual) information. However, if this is done, be sure
to provide a text equivalent
describing meaning of the bullet:
This section discusses the accessibility of tables and elements
that one can put in a TABLE element. Two types of
tables are discussed: tables used to organize data, and tables used to
create a visual layout of the page.
Content developers may make HTML 4.0
data tables more accessible in a number of
ways:
Identify structural
groups of rows (THEAD for repeated table headers, TFOOT for
repeated table footers, and TBODY for other groups of rows) and
groups of columns (COLGROUP and COL). Label table elements with the
"scope",
"headers", and
"axis" attributes so that future browsers
and assistive technologies will be able to select data from a table
by filtering on categories. This markup will also help browsers
linearize tables (also called table "serialization".
A row-based linear version may be created by reading
the row header, then preceding each cell with the cell's column header.
Or, the linearization might be column-based.
Note that the natural language writing direction
may affect column layout (and thus ordering). In HTML,
the "dir"
attribute specifies column layout order (e.g.,
dir="rtl" specifies right-to-left layout).
Do not use PRE to create a tabular
layout of text -- use the TABLE element so that assistive technologies
may recognize that it is a table.
Provide a summary via the "summary"
attribute. Summaries are especially useful for non-visual
readers.
Provide
terse substitutes for header labels with the
"abbr" attribute on
TH. These will be particularly useful for future speaking
technologies that can read row and column labels for each cell.
Abbreviations cut down on repetition and reading time.
Future browsers and assistive
technologies will be able to automatically translate tables into
linear sequences or navigate a table cell by cell if data is labeled
appropriately. The WAI Evaluation and Repair working group is tracking
the progress of tools as well as developing their own
that will allow users to navigate tables cell by cell. Refer to
[WAI-ER].
This markup will allow accessible browsers and other user agents
to restructure or navigate tables in a non-visual manner.
For information about table headers, refer to the table
header algorithm and discussion in the HTML 4.0
Recommendation ([HTML40], section 11.4.3).
Example.
This example shows how to associate data cells
(created with TD) with
their corresponding headers by means of the
"headers" attribute.
The "headers" attribute specifies a list of header cells (row and
column labels) associated with the current data cell. This requires
each header cell to have an "id" attribute.
Cups of coffee consumed by each senator
Name
Cups
Type of Coffee
Sugar?
T. Sexton
10
Espresso
No
J. Dinnen
5
Decaf
Yes
End example.
A speech synthesizer might render this tables as follows:
Caption: Cups of coffee consumed by each senator
Summary: This table charts the number of cups of coffee
consumed by each senator, the type of coffee
(decaf or regular), and whether taken with sugar.
Name: T. Sexton, Cups: 10, Type: Espresso, Sugar: No
Name: J. Dinnen, Cups: 5, Type: Decaf, Sugar: Yes
A visual user agent might render this table as follows:
The next example associates the same header (TH) and data (TD)
cells as before, but this time uses the "scope" attribute rather than "headers". "Scope" must have one of the following
values: "row", "col", "rowgroup", or "colgroup." Scope specifies the set of
data cells to be associated with the current header cell. This method
is particularly useful for simple tables. It should be noted that the
spoken rendering of this table would be identical to that of the
previous example. A choice between the "headers" and "scope"
attributes is dependent on the complexity of the table. It does not
affect the output so long as the relationships between header and data
cells are made clear in the markup.
Example.
Cups of coffee consumed by each senator
Name
Cups
Type of Coffee
Sugar?
T. Sexton
10
Espresso
No
J. Dinnen
5
Decaf
Yes
End example.
The following example shows how to create categories within a
table using the "axis" attribute.
Example.
Travel Expense Report
Meals
Hotels
Transport
subtotals
San Jose
25-Aug-97
37.74
112.00
45.00
26-Aug-97
27.28
112.00
45.00
subtotals
65.02
224.00
90.00
379.02
Seattle
27-Aug-97
96.25
109.00
36.00
28-Aug-97
35.00
109.00
36.00
subtotals
131.25
218.00
72.00
421.25
Totals
196.27
442.00
162.00
800.27
End example.
This table lists travel expenses at two locations: San Jose and
Seattle, by date, and category (meals, hotels, and transport). The
following image shows how a visual user agent might render it.
[Description of
travel table]
Authors should use style sheets for
layout and positioning. However, when it is necessary to use a
table for layout, the table must linearize in a readable order. When
a table is linearized, the contents of the cells become a series of
paragraphs (e.g., down the page) one after another. Cells should make
sense when read in order (row-wise or column-wise)
and should include structural elements (that
create paragraphs, headers, lists, etc.) so the page makes sense after
linearization.
Also, when using tables to create a layout, do not use structural
markup to create visual formatting. For example, the TH (table
header) element, is usually displayed visually as centered, and
bold. If a cell is not actually a header for a row or column
of data, use style sheets or formatting attributes of the
element.
Tables used to lay out pages and some data
tables where cell text wraps pose problems for older screen
readers that do not interpret the source HTML or browsers that do not
allow navigation of individual table cells. These screen readers will
read across the page, reading sentences on the same row from different
columns as one sentence.
For example, if a table is rendered like this on the screen:
There is a 30% chance of Classes at the University of Wisconsin
rain showers this morning, but they will resume on September 3rd.
should stop before the weekend.
This might be read by a screen reader as:
There is a 30% chance of Classes at the University of Wisconsin
rain showers this morning, but they will resume on September 3rd.
should stop before the weekend.
Screen readers that read the source HTML will recognize the
structure of each cell, but for older screen readers, content
developers may minimize the risk of word wrapping by limiting the
amount of text in each cell. Also, the longest chunks of text should
all be in the last column (rightmost for left-to-right tables). This
way, if they wrap, they will still be read coherently. Content
developers should test tables for wrapping with a browser window
dimension of "640x480".
Since table markup is structural, and we suggest separating structure
from presentation, we recommend using style sheets to create layout,
alignment, and presentation effects. Thus, the two columns in the
above example could have been created using style sheets. Please refer
to the section on style sheets for more information.
Quicktest! To get a better
understanding of how a screen reader would read a table, run a
piece of paper down the page and read your table line by line.
Good link text should not be overly general; don't use "click
here." Not only is this phrase device-dependent (it implies a pointing
device) it says nothing about what is to be found if the link if
followed. Instead of "click here", link text should indicate the
nature of the link target, as in "more information about sea lions" or
"text-only version of this page". Note that for the latter case (and
other format- or language-specific documents), content developers are
encouraged to use content
negotiation instead, so that users who prefer text versions will
have them served automatically.
In addition to clear link text, content developers may specify a
value of the "title" attribute that clearly and accurately describes
the target of the link.
If two or more links refer to different targets but share the same
link text, distinguish the links by specifying a different value for
the "title" attribute of each A element.
"Auditory users" -- people who are blind,
have difficulty seeing, or who are using
devices with small or no displays -- are unable to scan the
page quickly with their eyes. To get an overview of a page or to
quickly find a link, these users will often tab from one link
to the next or review a list of available links on a page.
Thus, for a series of related links, include introductory
information in the first link, then distinguishing information in the
links that follow. This will provide context information for
users reading them in sequence.
When links are grouped into logical sets (for example,
in a navigation bar that appears on every page in a
site) they should be marked up as a unit.
Navigation bars are usually the first thing someone encounters on a page.
For users with speech synthesizers, this means having to hear
a number of links on every page before reaching the interesting
content of a page. There are several ways to allow users to
bypass groups of links (as users with vision do
when they see the same set on each page):
Include a link that allows users to skip over
the set of navigation links.
Use the HTML 4.0 "tabindex"
attribute to allow users to jump to an anchor after the set of
navigation links. This attribute is not yet widely supported.
Provide a style sheet that allows users to hide
the set of navigation links.
In the future, user agents will allow users to skip
over elements such as navigation bars.
In HTML, use the DIV, SPAN, P, or FRAME elements to group
links then identify the group with the "id"
or "class"
attributes.
Example.
In this example, the P element groups a
set of links, the "class" attribute identifies it as a navigation bar
(e.g., for style sheets), "tabindex" is set
on an anchor following the group, and a link at the beginning of the
group links to the anchor after the group.
Keyboard access to active elements of a page is important
for many users who cannot use a pointing device. User agents
may include features that allow users to bind keyboard strokes
to certain actions. HTML 4.0 also allows content developers
to specify keyboard shortcuts in documents via
the "tabindex" attribute.
Example.
In this example, if the user activates the "C" key, the link will
be followed.
When a short text equivalent does not suffice to adequately convey
the function or role of an image, provide additional information in a
file designated by the "longdesc" attribute:
Example.
In sales97.html:
A chart showing how sales in 1997 progressed. The
chart
is a bar-chart showing percentage increases in sales
by month. Sales in January were up 10% from December 1996,
sales in February dropped 3%, ..
When using OBJECT, specify the the longer text equivalent
within the element's content:
Example.
End example.
Note that OBJECT content, unlike "alt" text, can include markup.
Thus, content developers can provide a link to additional information
from within the OBJECT element:
Note. Invisible d-links are deprecated
in favor of the "longdesc" attribute.
An invisible d-link is a small
(1-pixel) or transparent image whose "alt"
attribute value is "D-link" or "D" and is part of the
content of an A element. Like
other d-links, it refers to a text equivalent
of the associated image. Like other links, users can tab to it.
Invisible d-links thus provide a (temporary)
solution for designers who wish to avoid visible d-links for
stylistic reasons.
Avoid ascii art (character
illustrations) and use real images instead since it is easier to
supply a text equivalent for images.
However, if ascii art must be used provide a link to jump over the
ASCII art, as follows.
If the ASCII art is complex, ensure that the text equivalent
adequately describes it.
Another way to replace ascii art is to use human language
substitutes. For example, might substitute for
a winking smiley: ;-).
Or, the word "therefore" can replace arrows consisting of dashes and greater
than signs (e.g., -->), and the word "great" for the uncommon
abbreviation "gr8".
An image map is an image that has "active regions". When the
user selects one of the regions, some action takes place -- a link
may be followed, information may be sent to a server, etc. To make an
image map accessible, content developers must ensure that each action
associated with a visual region may be activated without a pointing
device.
Image maps are created with the MAP element.
HTML allows two types of image maps: client-side (the
user's browser processes a URI) and server-side (the server
processes click coordinates). For all image maps, content developers must
supply a text equivalent.
Content developers should create client-side image maps (with
"usemap") rather than server-side image
maps (with "ismap") because server-side
image maps require a specific input device. If server-side image maps
must be used (e.g., because the geometry of a region cannot be
represented with values of the shape
attribute), authors must provide the same functionality or information
in an alternative accessible format. One way to achieve this is to
provide a textual link for each active region so that each link is
navigable with the keyboard. If you must use a
server-side image map, please consult the section on server-side image maps
Provide
text equivalents for image maps since they convey visual information.
If AREA is used to create the map, use
the "alt" attribute:
Example.
End example.
The following example illustrates the same idea, but uses OBJECT instead of IMG to insert the image to
provide more information about the image:
Example.
End example.
In addition to providing a text equivalent, provide redundant
textual links. If the A element is used
instead of AREA, the content developer may describe the active regions
and provide redundant links at the same time:
Note that in the previous example, the MAP element is the content
of the OBJECT element so that the alternative links will only be
displayed if the image map (navbar1.gif) is not.
Note also that links have been separated by brackets ([]). This
is to prevent older screen readers from reading several adjacent links as
a single link as well as helps sighted users distinguish between
links visually.
Content developers should make
sure they include printable characters (such as brackets or a
vertical bar (|)) surrounded by spaces between adjacent
links.
If IMG is used to insert the image,
provide an alternative list of links after it and
indicate the existence and location of the alternative list
(e.g., via that "alt"
attribute).
A more complex example takes advantage of the fact the OBJECT
elements may be embedded to provide for alternative representations
of information:
Example.
End example.
If APPLET is used,
provide a text equivalent
with the "alt" attribute
and in the content in the APPLET element. This enables
the content to transform
gracefully for those user agents that only support one of the two
mechanisms ("alt" or content).
If an applet (created with either OBJECT
or APPLET) requires user interaction
(e.g., the ability to manipulate a physics experiment) that cannot be
duplicated in an alternative format, make the applet directly
accessible.
For more information about developing accessible applets,
please refer to [JAVAACCESS] and
[IBMJAVA]. These companies have been
developing an Accessibility API as well as making the Java Swing
classes accessible.
Provide a
text equivalent as for an image
and
auditory descriptions of visual information and captions where necessary.
If an applet creates motion, developers should provide a mechanism for freezing
this motion
(for an example, refer to [TRACE]).
Also, please refer to the next section for information about making
audio and video presentations accessible.
Auditory presentations must be accompanied by text
transcripts, textual equivalents of auditory events. When these
transcripts are presented synchronously with a video presentation they
are called captions and are used by people who cannot hear the
audio track of the video material.
Some media formats (e.g., QuickTime 3.0 and SMIL) allow captions
and video descriptions to be added to the multimedia clip.
SAMI allows captions to be added. The following example demonstrates
that captions should include speech as well as other sounds in the
environment that help viewers understand what is going on.
Example.
Captions for a scene from "E.T." The phone rings three times,
then is answered.
[phone rings]
[ring]
[ring]
Hello?"
End example.
Until the format you are using supports alternative tracks, two
versions of the movie could be made available, one with captions and
descriptive video, and one without. Some technologies, such as SMIL
and SAMI, allow separate audio/visual files to be combined with text
files via a synchronization file to create captioned audio and movies.
Some technologies also allow the user to choose from multiple sets
of captions to match their reading skills. For more information see
the SMIL 1.0 ([SMIL]) specification.
Equivalents for sounds can be provided in the form of a text phrase
on the page that links to a text transcript or description of the
sound file. The link to the transcript should appear in a highly
visible location such as at the top of the page. However, if a script
is automatically loading a sound, it should also be able to
automatically load a visual indication that the sound is currently
being played and provide a description or transcript of the sound.
Note. Some controversy surrounds this technique
because the browser should load the visual form of the information
instead of the auditory form if the user preferences are set to do
so. However, strategies must also work with today's browsers.
Auditory descriptions of the visual track provide narration
of the key visual
elements without interfering with the audio or dialogue of a movie.
Key visual elements include actions, settings, body language,
graphics, and displayed text. Auditory descriptions are used primarily by
people who are blind to
follow the action and other non-auditory information in video
material.
Example.
Here's an example of a collated text transcript
of a clip from "The Lion King"
(available at [DVS]). Note that the Describer is
providing the auditory description of the video track and that the description
has been integrated into the transcript.
Simba: Yeah!
Describer: Simba races outside, followed by his parents. Sarabi
smiles and nudges Simba gently toward his father. The two sit
side-by-side, watching the golden sunrise.
Mufasa: Look Simba, everything the light touches is our
kingdom.
Simba: Wow.
End example.
Note. If there is no important visual information, for example,
an animated talking head that describes (through prerecorded
speech) how to use the site, then an auditory description is not necessary.
For movies,
provide auditory descriptions that are synchronized with the original
audio. Refer to the section on audio
information for more information about multimedia formats.
Collated text transcripts
allow access by people with both visual and hearing
disabilities. They also provide everyone with the ability to index
and search for information contained in audio/visual materials.
Collated text transcripts include spoken dialogue as well as
any other significant sounds including on-screen and off-screen
sounds, music, laughter, applause, etc. In other words, all of the text
that appears in captions as well as all of the descriptions provided
in the auditory description.
When necessary, a
text equivalent should be provided for visual
information to enable understanding of the page.
For example, consider
a repeating animation that shows cloud cover and precipitation as
part of a weather status report. Since
the animation is supplementing the rest of the weather report (that is presented
in natural language - text), a less verbose description of the
animation is necessary. However, if the animation appears in a pedagogical
setting where students are learning about cloud formations
in relation to land mass, then the animation ought to be described for those
who can not view the animation but who also want to learn the lesson.
See also the section on text style for
controlling blinking.
Other objects, such as those requiring
a plug-in, should also use the
OBJECT element. However, for backward compatibility with Netscape
browsers, use the proprietary EMBED element within the OBJECT element
as follows:
For visually enabled users, frames may organize a page into
different zones. For non-visual users, relationships between the
content in frames (e.g., one frame has a table of contents, another
the contents themselves) must be conveyed through other means.
Frames as implemented today
(with the FRAMESET,
FRAME, and
IFRAME elements)
are problematic for several reasons:
Without scripting, they tend to break the "previous page"
functionality offered by browsers.
It is impossible to refer to the "current state" of
a frameset with a URI; once a frameset changes contents, the
original URI no longer applies.
Opening a frame in a new browser window can disorient
or simply annoy users.
In the following sections, we discuss how to make frames more
accessible. We also provide an alternative
to frames that uses HTML 4.0 and CSS and addresses many
of the limitations of today's frame implementations.
#Navbar - this frame provides links to the major
sections of the site: World News, National News,
Local News, Technological News,
and Entertainment News.
#Story - this frame displays the currently selected story.
#Index - this frame provides links to the day's
headline stories within this section.
End example.
Note that if the a frame's contents change, the
text equivalent will no longer apply. Also, links to descriptions
of a frame should be provided along with other alternative content
in the NOFRAMES element of a FRAMESET.
Content developers must provide text equivalents of frames so that
their contents and the relationships between frames make sense. Note
that as the contents of a frame change, so must change any
description. This is not possible if an IMG is inserted directly into
a frame. Thus, content developers should always make the source
("src") of a frame an HTML file. Images may be inserted into the HTML
file and their text alternatives will evolve correctly.
Example.
A correct frameset document
End example.
The following deprecated example should be avoided
since it inserts IMG
directly in a frame:
Deprecated example.
A bad frameset document
Note that if, for example, a link causes a new image to be
inserted into the frame:
One of the most common uses of frames is to split the
user's browser window into two parts: a navigation window
and a content window. As an alternative to frames, we
encourage you to try the following:
Create one document for the navigation mechanism (call it
"nav.html"). A separate document means that the navigation
mechanism may be shared by more than one document.
In each document requiring the navigation mechanism,
include it at the bottom of the document with the following
(or similar) OBJECT markup:
Example.
Putting the navigation mechanism at the end of the
document means that when style sheets are turned off,
users have access to the document's important information first.
Use style sheets to position the navigation mechanism
where you want on the screen.
For example, the following CSS rule floats
the navigation bar to the left of the page and makes it take
up 25% of the available horizontal space:
OBJECT { float: left; width: 25% }
The following CSS rule attaches the navigation
mechanism to the bottom-left corner of the page of the page
and keeps it there even if the user scrolls down the page:
OBJECT { position: fixed; left: 0; bottom: 0 }
Note. Navigation mechanisms or other
content may be inserted in a document by means of
server-side includes.
Content developers should group
information where natural and appropriate. When form controls can
be grouped into logical units, use the FIELDSET element and label
those units with the LEGEND element:
Content developers should group
information where natural and appropriate. For long lists of menu
selections (which may be difficult to track), content developers should
group SELECT
items (defined by OPTION)
into a hierarchy using the OPTGROUP
element. Specifies a label for the group of options
with the label attribute on OPTGROUP.
In the next example, we specify a tabbing order among elements (in
order, "field2", "field1", "submit") with "tabindex":
Example.
End example.
This example assigns "U" as the accesskey (via "accesskey"). Typing "U" gives focus to the label,
which in turn gives focus to the input control, so that the user can
input text.
Using images to decorate buttons allows developers to make their
forms unique and easier to understand. Using an image for a button
(e.g., with the INPUT element or BUTTON) is not inherently inaccessible -
assuming a text equivalent is provided for the image.
However, a graphical form submit button created with INPUT, type="image" creates a type of server-side
image map. Whenever the button is clicked with a mouse, the x and y
coordinates of the mouse click are sent to the server as part of the
form submission.
In the Image and Image Maps
section, we discuss why server-side images
ought to be avoided, and suggest using client-side image maps instead.
In HTML 4.0, graphical buttons may now be client-side image maps. To preserve
the functionality provided by the server, authors have the following
options, as stated in the HTML 4.0 Recommendation ([HTML40], section 17.4.1):
If the server takes different actions depending on the location
clicked, users of non-graphical browsers will be disadvantaged.
For this reason, authors should consider alternate approaches:
Use multiple submit buttons (each with its own image) in place
of a single graphical submit button. Authors may use style
sheets to control the positioning of these buttons.
Use a client-side image map together with scripting.
Content developers must ensure that pages are accessible with scripts
turned off or in browsers that don't support scripts.
Avoid creating content on the fly on the client.
If a user's browser does not handle scripts,
no content will be generated or displayed.
However, this is different than displaying
or hiding already existing content by
using a combination of style sheets and scripting; if there
is no script, then the content is always shown. This also does not rule out
generating pages on the fly on the server-side and
delivering them to the client.
Avoid creating links that use "javascript" as the URI. If
a user is not using scripts, then they won't be able to link since the
browser can't create the link content.
Deprecated example. This is a dead-end link for a user agent where scripts
are not supported or not loaded.
An event handler is a script that is invoked when a certain event
occurs (e.g, the mouse moves, a key is pressed, the document is
loaded, etc.). In HTML 4.0, event handlers are attached to elements
via event handler attributes
(the attributes beginning with "on", as in "onkeyup").
Some event handlers, when invoked, produce purely decorative
effects such as highlighting an image or changing the color of an
element's text. Other event handlers produce much more substantial
effects, such as carrying out a calculation, providing important
information to the user, or submitting a form. For event handlers that
do more than just change the presentation of an element, content developers
should do the following:
Use application-level event triggers rather than
user interaction-level triggers. In HTML 4.0, application-level
event attributes are "onfocus", "onblur" (the opposite of "onfocus"),
and "onselect". Note that these attributes are designed to be
device-independent, but are implemented as keyboard specific events
in current browsers.
Otherwise, if you must use device-dependent attributes,
provide redundant input mechanisms (i.e., specify two
handlers for the same element):
Use "onmousedown" with "onkeydown".
Use "onmouseup" with "onkeyup"
Use "onclick" with "onkeypress"
Note that there is no keyboard equivalent to double-clicking
("ondblclick") in HTML 4.0.
Do not write event handlers that rely on mouse
coordinates since this prevents device-independent input.
The following sections list some techniques for using CSS to design
accessible documents and some techniques for writing effective style
sheets. In HTML, style sheets may be specified externally via the
LINK element, in the document head via the
STYLE element, or for a specific element
via the style attribute.
CSS1 ([[CSS1]) and CSS2 ([[CSS2]) allow content developers to duplicate
most HTML 4.0 presentation capabilities and offer more power with less
cost. However, until most users have browsers that support style
sheets, not every presentation idiom may be expressed
satisfactorily with style sheets. We
also provide examples of how to use HTML 4.0 features (e.g.,
tables, bitmap text) more accessibly when they must be used.
Here are guidelines for creating style sheets that
promote accessibility:
Use a minimal number of style sheet for your site
If you have more than one, use the same "class" name for the same
concept in all of the style sheets.
Use linked style sheets rather than embedded styles, and avoid
inline style sheets.
Content developers should not write "!important" rules. Users should
where necessary.
Use the "em" unit to set font sizes.
Use relative length units and percentages. CSS allows you to
use relative units even in absolute positioning.
Thus, you may position an image to be offset by "3em" from
the top of its containing element. This is a fixed distance,
but is relative to the current font size, so it scales
nicely.
Only use absolute length units when the physical characteristics of
the output medium are known.
Always specify a fallback generic font.
Use numbers, not names, for colors.
Provide a text equivalent
for any important image or text generated by style sheets
(e.g., via the 'background-image', 'list-style', or 'content'
properties). Note.
Text generated by style sheets is part of the document
source and will not be available to
assistive technologies that access content through
DOM, level 1 ([DOM1]).
Be sure to validate
that your pages are still readable
without style sheets.
Some examples follow.
Example.
Use em to set font sizes, as in:
H1 { font-size: 2em }
rather than:
H1 { font-size: 12pt }
End example.
Example.
Use relative length units and percentages.
BODY { margin-left: 15%; margin-right: 10%}
End example.
Example.
Only use absolute length units when the physical characteristics of
the output medium are known.
Instead of using deprecated presentation
elements and attributes , use the many CSS properties to control
font characteristics: 'font-family', 'font-size',
'font-size-adjust', 'font-stretch', 'font-style', 'font-variant',
and 'font-weight'.
The following CSS2 properties can be used to control
font information: 'font', 'font-family', 'font-size', 'font-size-adjust',
'font-stretch', 'font-style', 'font-variant', and 'font-weight'.
Use them instead of the following deprecated font elements and
attributes in HTML: FONT,
BASEFONT, "face", and "size".
If you must use HTML elements to control font information, use
BIG and SMALL, which are not deprecated.
The following CSS2 properties can be used to style text:
Case: 'text-transform' (for uppercase, lowercase, and
capitalization).
Shadow effects: 'text-shadow'
Underlines, overlinks, blinking: 'text-decoration'.
Note. If blinking content (e.g., a headline
that appears and disappears at regular intervals) is used,
provide a mechanism for stopping the blinking. In CSS,
'text-decoration: blink' will cause content to blink and will
allow users to stop the effect by turning off style sheets
or overriding the rule in a user style sheet.
Do not use the BLINK and MARQUEE
elements. These elements are not part of any W3C specification for
HTML (i.e., they are non-standard elements).
Content developers should use style sheets to style
text rather than representing text in images. Using
text instead of images means that the information will be
available to a greater number of users (with speech synthesizers,
braille displays, graphical displays, etc.). Using style sheets
will also allow users to override author styles and change colors
or fonts sizes more easily.
The following CSS2 properties can be used to control
the formatting and position of text:
Indentation: 'text-indent'.
Do not use the BLOCKQUOTE or any other structural element to indent
text.
Letter/word spacing: 'letter-spacing', 'word-spacing'.
For example instead of writing "H E L L O" (which
users generally recognize as the word "hello" but would hear as individual
letters), authors may create the same visual effect with the
'word-spacing' property applied to "HELLO".
Text without spaces will be transformed
more effectively to speech.
White space: 'white-space'. This property controls
the white space processing of an element's content.
Text direction: 'direction', 'unicode-bidi'.
The :first-letter and :first-line pseudo-elements
allow authors to refer to the first letter or line of
a paragraph of text.
The following example shows how to use style sheets
to create a drop-cap effect.
Example.
Drop caps
Once upon a time...
Note. As of the writing of this document, the
CSS pseudo-element ':first-letter', which allows content developers to refer
to the first letter of a chunk of text, is not widely
supported.
'border-color', 'outline-color' for border colors.
For link colors, refer to the :link, :visited, and :active
pseudo-classes.
Ensure that information is not conveyed through color alone. For
example, when asking for input from users, do not write "Please select
an item from those listed in green." Instead, ensure that
information is available through other style effects (e.g.,
a font effect) and through context (e.g,. comprehensive
text links).
For instance, in this document, examples are styled by default
(through style sheets) as follows:
They are surrounded by a border.
They use a different background color.
They begin with the word "Example" (or "Deprecated
Example".
They also end with the phrase "End example", but that
phrase is hidden by default with 'display: none'. For
user agents that don't support style sheets or when
style sheets are turned off, this text helps delineate
the end of an example for readers who may not be
able to see the border around the example.
Quicktest! To test whether your
document still works without colors, examine it with a monochrome
monitor or browser colors turned off. Also, try setting up a color
scheme in your browser that only uses black, white, and the four
browser-safe greys and see how your page holds up.
Quicktest! To test whether color
contrast is sufficient to be read by people with color deficiencies or
by those with low resolution monitors, print pages on a black and
white printer (with backgrounds and colors appearing in
grayscale). Also try taking the printout and copying it for two or
three generations to see how it degrades. This will show you where you
need to add redundant cues (example: hyperlinks are usually underlined
on Web pages), or whether the cues are two small or indistinct to hold
up well.
For more information about colors and contrasts, refer
to [LIGHTHOUSE].
Layout, positioning, layering, and alignment should be done through style
sheets (notably by using CSS floats and absolute positioning):
'text-indent', 'text-align', 'word-spacing', 'font-stretch'. Each
of these properties allows users to control spacing without adding additional
spaces. Use 'text-align: center' instead of the deprecated
CENTER element.
'margin', 'margin-top', 'margin-right', 'margin-bottom',
'margin-left'. With these properties, authors can create space
on four sides of an element's content instead of adding
non-breaking spaces ( ),
which are non-standard mark-up, to create space around an element.
'float', 'position', 'top', 'right', 'bottom',
'left'. With these properties, the user can
control the visual position of almost any element in a manner
independent of where the element appears in the document. Authors
should always design documents that make sense
without style sheets (i.e., the document should
be written in a "logical" order)
and then apply style sheets to achieve visual effects.
The positioning properties may be used to create
margin notes (which may be automatically numbered), side bars,
frame-like effects, simple headers and footers, and more.
The 'empty-cells' property allows users to leave
table cells empty and still give them proper borders on the
screen or on paper. A data cell that is meant to be empty should
not be filled with white space or a non-breaking space
just to achieve a visual effect.
If content developers cannot use style sheets and must use invisible or
transparent images (e.g., with IMG)
to lay out images on the page, they should
specify alt="" for them.
Deprecated example.
Authors should not use spaces for the value of
"alt" to prevents the words from running
together when the image is not loaded:
my poem requires a big spacehere
In this next example, an image is used to force a graphic to
appear in a certain position:
'border-spacing' and 'border-collapse' for tables.
'outline, 'outline-color', 'outline-style', and 'outline-width'
for dynamic outlines.
Authors should use style sheets to create rules and borders.
Example.
In this example, the H1
element will have a top border
that is 2px thick, red, and separated from the content
by 1em:
Redline with style sheets
Chapter 8 - Auditory and Tactile Displays
End example.
If a rule (e.g., the HR element)
is used to indicate
structure, be sure to indicate the structure in a non-visual way as
well. (e.g., by using structural markup).
Example.
In this example, the DIV element is used to create
a navigation bar, which includes a horizontal separator.
This index lists each checkpoint and the sections in this document
where it is discussed. Furthermore, each guideline number links to its
definition in the guidelines document. Each checkpoint
also links to its definition in the guidelines document.
This index lists all elements in HTML 4.0. The first column of this
table links to the definition of the element in the HTML 4.0
specification ([HTML40]). Elements that are
deprecated in HTML 4.0 are followed by an asterisk (*). Elements that
are obsolete in HTML 4.0 or don't exist in a W3C specification of HTML
(2.0, 3.2, 4.0) do not appear in this table.
The second column indicates other W3C specifications for HTML that
included each element. The third column indicates the element's role.
The last column lists the sections in the current document where
the element is discussed. An entry of "N/A" means that the element is
not discussed in this document.
This index lists some attributes in HTML 4.0 that affect
accessibility and what elements they apply to. The first column of
this table links to the definition of the attribute in the HTML 4.0
specification ([HTML40]).
Attributes and elements that are
deprecated in HTML 4.0 ([HTML40]) are
followed by an asterisk (*). Attributes and
elements that are obsolete in HTML 4.0 or
don't exist in a W3C specification of HTML (2.0, 3.2, 4.0) do not
appear in this table. Attributes that apply to most elements
of HTML 4.0 are indicated as such; please consult the HTML 4.0
specification for the exact list of elements with this attribute.
The second column indicates other W3C specifications for HTML that
included each attribute. The third column indicates the elements
that take each attribute. The fourth column
indicates the attribute's role.
The last column lists the sections in the current document where the
attribute is discussed. An entry of "N/A" means that the attribute is
not discussed in this document.
The following is the list of HTML 4.0 attributes not directly
related to accessibility. Content developers should use style sheets
instead of presentation attributes. For even handler attributes,
please refer to the section on
device-independent event handlers for more detail.
We wish to thank the following people who have contributed their
time and valuable comments to shaping these guidelines:
Harvey Bingham, Kevin Carey, Chetz Colwell, Neal Ewers, Geoff
Freed, Al Gilman, Larry Goldberg, Jon Gunderson, Eric Hansen,
Phill Jenkins, Leonard
Kasday, George Kerscher, Marja-Riitta Koivunen, Josh Krieger, Scott
Luebking, William Loughborough, Murray Maloney, Charles
McCathieNevile, MegaZone (Livingston Enterprises), Masafumi Nakane,
Mark Novak, Charles Oppermann, Mike Paciello, David Pawson, Michael Pieper,
Greg Rosmaita, Liam Quinn, Dave Raggett, T.V. Raman, Robert
Savellis, Jutta Treviranus, Steve Tyler, Jaap van Lelieveld, and
Jason White
The original draft of this document is based on "The Unified Web
Site Accessibility Guidelines" ([UWSAG])
compiled by the Trace R & D Center at the University of Wisconsin.
That document includes a list of additional contributors.
"Document Object Model (DOM) Level 1 Specification",
V. Apparao, S. Byrne, M. Champion, S. Isaacs, I. Jacobs, A. Le Hors, G. Nicol,
J. Robie, R. Sutor, C. Wilson, and L. Wood, eds., 1 October 1998.
The DOM Level 1 Recommendation is:
http://www.w3.org/TR/1998/REC-DOM-Level-1-19981001.
The latest version of DOM Level 1 is available at:
http://www.w3.org/TR/REC-DOM-Level-1
"PNG (Portable Network Graphics) Specification", T. Boutell, ed.,
T. Lane, contributing ed., 1 October 1996.
The latest version of PNG 1.0 is:
http://www.w3.org/TR/REC-png.
"Techniques for Web Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, I. Jacobs, eds.
This document explains how to implement the checkpoints defined
in "Web Content Accessibility Guidelines 1.0". The latest draft of the techniques is
available at:
http://www.w3.org/TR/WAI-WEBCONTENT-TECHS/
"Authoring Tool Accessibility Guidelines", J. Treviranus,
J. Richards, I. Jacobs, C. McCathieNevile, eds.
The latest Working Draft of these guidelines for designing
accessible authoring tools is available at:
http://www.w3.org/TR/WAI-AUTOOLS/
This page documents known support by user agents (including
assistive technologies) of some accessibility features listed
in this document. The page is available at:
http://www.w3.org/WAI/Resources/WAI-UA-Support
"User Agent Accessibility Guidelines", J. Gunderson
and I. Jacobs, eds.
The latest Working Draft of these guidelines for designing accessible
user agents is available at:
http://www.w3.org/TR/WAI-USERAGENT/
"The Unified Web Site Accessibility Guidelines", G.
Vanderheiden, W. Chisholm, eds.
The Unified Web Site Guidelines were compiled by the
Trace R
& D Center at the University of Wisconsin under funding from the
National Institute on Disability and Rehabilitation Research
(NIDRR), U.S. Dept. of Education. This document is
available at:
http://www.tracecenter.org/docs/html_guidelines/version8.htm
Spool, J.M., Sconlong, T., Schroeder, W., Snyder, C., DeAngelo, T. (1997).
Web Site Usability: A Designer's Guide
User Interface Engineering, 800 Turnpike St,
Suite 101, North Andover, MA 01845.
Walsh, Norman. (1997). "A Guide to XML." In "XML: Principles, Tools,
and Techniques." Dan Connolly, Ed. O'Reilly & Associates, 101 Morris St,
Sebastopol, CA 95472. pp 97-107.
Audrey
Roth IRA
401(k)
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