
- This version:
-
http://www.w3.org/TR/2002/WD-UAAG10-TECHS-20020821/
- Latest version:
-
http://www.w3.org/TR/UAAG10-TECHS/
- Previous version:
-
http://www.w3.org/TR/2001/WD-UAAG10-TECHS-20010912/
- Editors:
- Ian Jacobs, W3C
Jon Gunderson, University of Illinois at
Urbana-Champaign
Eric Hansen, Educational Testing
Service
- Authors and Contributors:
- See acknowledgements.
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Copyright © 1999 - 2002 W3C® (MIT,
INRIA, Keio), All Rights
Reserved. W3C
liability,
trademark, document
use and software
licensing rules apply.
This document provides techniques for satisfying the checkpoints defined in
"User Agent Accessibility Guidelines 1.0" [UAAG10]. These techniques address
key aspects of the accessibility of user interfaces, content rendering,
application programming interfaces (APIs), and languages
such as the Hypertext Markup Language (HTML), Cascading Style Sheets
(CSS) and the Synchronized
Multimedia Integration Language (SMIL).
The techniques listed in this document are not required for conformance to
the Guidelines. These techniques are not necessarily the only way of satisfying
the checkpoint, nor are they a definitive set of requirements for satisfying a
checkpoint.
This section describes the status of this document at the time of its
publication. Other documents may supersede this document. The latest status of
this document series is maintained at the W3C.
This is the 21 August 2002 Working Draft of "Techniques for User Agent
Accessibility Guidelines 1.0". It is a draft document and may be updated,
replaced or obsoleted by other documents at any time. It is inappropriate to
use W3C Working Drafts as reference material or to cite them as other than
"work in progress". This is work in progress and does not imply endorsement by,
or the consensus of, either W3C or participants in the User Agent Accessibility
Guidelines Working Group (UAWG).
While User Agent 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 Web sites and pages.
A list of changes
to this document is available.
The latest information regarding patent
disclosures related to this document is available on the Web. As of this
publication, there are no disclosures.
Please send comments about this document, including suggestions for
additional techniques, to the public mailing list w3c-wai-ua@w3.org; public archives are
available.
This document is part of a series of accessibility documents published by
the Web Accessibility Initiative (WAI) of the World Wide Web
Consortium (W3C). WAI
Accessibility Guidelines are produced as part of the WAI Technical Activity. The
goals of the User Agent Accessibility
Guidelines Working Group are described in the charter.
A list of current W3C Recommendations and
other technical documents can be found at the W3C Web site.
This document discusses implementation details that should be helpful to
understanding how to satisfy the requirements of "User Agent Accessibility
Guidelines 1.0"
[UAAG10]. This document includes:
- This section provides some context for using this document.
- Section 2 lists each checkpoint of "User Agent
Accessibility Guidelines 1.0" along with some possible techniques for
satisfying it.
- Section 3 discusses general topics
related to the implementation of accessibility features in user agents.
In an effort to improve the readability of this document, some information
from User Agent Accessibility Guidelines 1.0 has been copied here:
In an effort to reduce the size of the current document, some information
that is in User Agent Accessibility Guidelines 1.0 has not been copied
here:
- the introduction;
- the descriptions of how the guidelines and checkpoints are structured and
organized;
- the prose of each guideline (i.e., the text after the guideline title and
before the list of checkpoints);
- the conformance section (since one does not conform to the current
document, only to User Agent Accessibility Guidelines 1.0).
The current document includes a list of references
resources that is not part of User Agent Accessibility
Guidelines 1.0.
"Techniques for User Agent Accessibility Guidelines 1.0" and the "User Agent
Accessibility Guidelines 1.0" are part of a series of accessibility guidelines
published by the Web Accessibility
Initiative (WAI).
These documents explain the responsibilities of user agent developers in making
the Web more accessible to users with disabilities. The series also includes
the "Web Content Accessibility Guidelines 1.0" [WCAG10] (and techniques
[WCAG10-TECHS]), which explain the responsibilities of authors, and
the "Authoring Tool Accessibility Guidelines 1.0" [ATAG10] (and techniques
[ATAG10-TECHS]), which explain the responsibilities of authoring
tool developers.
This section lists each checkpoint of "User Agent Accessibility Guidelines
1.0"
[UAAG10] along with some possible techniques for satisfying it. Each
checkpoint definition includes a link to the checkpoint definition in "User
Agent Accessibility Guidelines 1.0". Each checkpoint definition is followed by
one or more of the following:
- Notes and rationale: Additional rationale and explanation
of the checkpoint;
- Who benefits: Which users with disabilities are expected
to benefit from user agents that satisfy the checkpoint;
- Example techniques: Some techniques to illustrate how a
user agent might satisfy the requirements of the checkpoint. Screen shots and
other information about deployed user agents have been included as sample
techniques. References to products are not endorsements of those products by
W3C;
- Doing more: Techniques to achieve more than what is
required by the checkpoint;
- Related techniques: Links to other techniques in section
3. The accessibility topics of section 3 generally apply to more than one
checkpoint.
- References: References to other guidelines,
specifications, or resources.
Note: Most of the techniques in this document are designed
for graphical browsers and multimedia players running on desktop computers.
However, some of them also make sense for assistive technologies and other user
agents. In particular, techniques about communication between user agents will
benefit assistive technologies. Refer, for example, to the appendix on loading assistive technologies for access to
the document object model.
Each checkpoint in this document is assigned a priority that indicates its
importance for users with disabilities.
- Priority 1
(P1)
- If the user agent does not satisfy this checkpoint, one or more groups of
users with disabilities will find it impossible to access the Web. Satisfying
this checkpoint is a basic requirement for enabling some people to access the
Web.
- Priority 2
(P2)
- If the user agent does not satisfy this checkpoint, one or more groups of
users with disabilities will find it difficult to access the Web. Satisfying
this checkpoint will remove significant barriers to Web access for some
people.
- Priority 3
(P3)
- If the user agent satisfies this checkpoint, one or more groups of users
with disabilities will find it easier to access the Web.
Note: This information about checkpoint priorities is
included for convenience only. For detailed information about conformance to
"User Agent Accessibility Guidelines 1.0" [UAAG10], please refer to that
document.
- Ensure that the user can operate
through keyboard input alone any user agent functionality available through the
user interface.
Note: For example, ensure that the user can interact with
enabled elements, select content,
navigate viewports, configure the user agent, access documentation, install the
user agent, operate user interface
controls, etc., all entirely through keyboard input.
User agents generally support at least three types of keyboard
operation:
- Direct (e.g., keyboard shortcuts such a "F1" to open the help menu; see checkpoint 11.4 for single-key
access requirements),
- Sequential (e.g., navigation
through cascading menus), and
- Spatial (e.g., when the keyboard is used to move the pointing device in two-dimensional visual space to manipulate a
bitmap image).
User agents should support direct or sequential keyboard operation for all
functionalities. Furthermore, the user agent should satisfy this checkpoint by
offering a combination of keyboard-operable user interface controls (e.g.,
keyboard operable print menus and settings) and direct keyboard shortcuts
(e.g., to print the current page).
It is also possible to claim conformance
to User Agent Accessibility Guidelines 1.0 [UAAG10] for full support through
pointing device input and/or voice input. See the section on Input
modality labels in UAAG 1.0.
Notes and rationale
- It is up to the user agent developer to decide which functionalities are
best served by direct access, sequential access, and access through two-dimensional visual space. The UAAG 1.0 does
not discourage a pointing device interface, but it does require redundancy
through the keyboard. In most cases, developers can allow operation of the user
agent without relying on motion through
two-dimensional visual space; this includes text selection (a text caret
may be used to establish the start and end of the selection), region selection
(allow the user to describe the coordinates or position of the region, e.g.,
relative to the viewport), drag-and-drop (allow the user to designate start and
end points and then say "go"), etc.
- For instance, the user must be able to do the following through the
keyboard alone (or pointing device alone or voice alone):
- Select content and operate on it. For
example, if the user can select rendered text with the mouse and make it the
content of a new link by pushing a button, they also need to be able to do so
through the keyboard and other supported devices. Other operations include cut,
copy, and paste.
- Set the focus on viewports and on enabled
elements.
- Install, configure, uninstall, and update the user agent software.
- Use the graphical user interface menus.
Some users may wish to use the graphical user interface even if they cannot use
or do not wish to use the pointing device.
- Fill out forms.
- Access documentation.
- Suppose a user agent such as a Web browser does not allow complete
operation through the keyboard alone. It is still possible to claim conformance
for the user agent in conjunction with another software component that "fills
in the gap".
Who benefits
- Users with blindness are most likely to benefit from direct access through
the keyboard, including navigation of user interface controls; this
is a logical navigation, not navigation in
two-dimensional visual space.
- Users with physical disabilities are most likely to benefit from a
combination of direct access and spatial access through the keyboard. For some
users with physical disabilities, moving the pointing device using a physical
mouse may be significantly more difficult than moving the pointing device with
arrow keys, for example.
- This checkpoint will also benefit users of many other alternative input
devices (which make use of the keyboard API) and also anyone without a
mouse.
- While keyboard operation is expected to improve access for many users,
operation by keyboard shortcuts alone may reduce accessibility (and usability)
by requiring users to memorize a long list of shortcuts. Developers should
provide mechanisms for contextual access to user agent functionalities
(including keyboard-operable cascading menus, context-sensitive help, keyboard
operable configuration tabs, etc.) as well as direct access to those
functionalities. See also
checkpoint 11.5.
- Allow the user to activate, through keyboard input alone, all
event handlers that are explicitly
associated with the element designated by the
content focus.
- In order to satisfy provision
one of this checkpoint, the user must be able to activate as a group all event
handlers of the same input device event type.
- Provision one of this checkpoint applies to handlers of any input
device event type, including event types for keyboard, pointing device, and
voice input.
- The user agent is not required to allow activation of event handlers
associated with a given device (e.g., the pointing device) in any order other
than what the device itself allows (e.g., a mouse down event followed by a
mouse drag event followed by a mouse up event).
- The requirements for this checkpoint refer to any
explicitly associated input device
event handlers associated with an element, independent of the input
modalities for which the user agent conforms. For example, suppose that an
element has an explicitly associated handler for pointing device events. Even
when the user agent only conforms for keyboard input (and does not conform for
the pointing device, for example), this checkpoint requires the user agent to
allow the user to activate that handler with the keyboard.
- This checkpoint is mutually exclusive of checkpoint 1.1 since it
may be excluded from a
conformance profile, unlike other keyboard operation requirements.
- Conformance
profile labels:
Events.
Note: Refer to the checkpoints of guideline 9 for more information about focus
requirements.
Notes and rationale
- For example, users without a pointing device need to be able to activate form controls and links (including
the links in a client-side image map).
- Events triggered by a particular device generally follow a set pattern, and
often in pairs: start/end, down/up, in/out. One would not expect a "key down"
event for a given key to be followed by another "key down" event without an
intervening "key up" event.
Who benefits
- Users with blindness or some users with a physical disability, and anyone
without a pointing device.
Example techniques
- When using the "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS], activate an event handler as described in
section 1.5:
- Create an event of the given type by calling
DocumentEvent.createEvent
, which takes an event type as parameter,
then
- Dispatch this event using
EventTarget.dispatchEvent
.
- To preserve the expected order of events, provide a dynamically changing
menu of available handlers. For example, an initial menu of handlers might only
allow the user to trigger a "mousedown" event. Once triggered, the menu would
not allow "mousedown" but would allow "mouseup" and "mouseover", etc.
- In some markup languages, it is possible (though somewhat nonsensical) for
two actions to be assigned to the same input event type for a given element
(e.g., one through an explicit event handler and one "intrinsic" to the
element). In this case, offer the user a choice of which action to take.
- For example, in HTML 4 [HTML4], input device event handlers
are described in
section 18.2.3. They are:
onclick
, ondblclick
,
onmousedown
, onmouseover
, onmouseout
,
onfocus
, onblur
, onkeypress
,
onkeydown
, and onkeyup
.
- In "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS], focus and activation types are discussed in
section 1.6.1. They are:
DOMFocusIn
, DOMFocusOut
,
and DOMActivate
. These events are specified independent of a
particular input device type.
- In "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS], mouse event types are discussed in
section 1.6.2. They are:
click
, mousedown
,
mouseup
, mouseover
, mousemove
and
mouseout
.
- The DOM Level 2 Events specification does not provide a key event
module.
- Sequential navigation
technique: Add each input device event handler to the navigation order (refer
to checkpoint 9.3). Alert the
user when the user has navigated to an event handler, and allow activation. For
example, an link that also has onMouseOver and onMouseOut event handlers
defined, might generate three "stops" in the navigation order: one for the link
and two for the event handlers. If this technique is used, allow configuration
so that input device event handlers are not inserted in the navigation
order.
- Query technique: Allow the user to query the element with content focus for
a menu of input device event handlers.
- Descriptive information about handlers can allow assistive technologies to
choose the most important functions for activation. This is possible in the
Java Accessibility API [JAVAAPI], which provides an an
AccessibleAction Java interface. This interface provides a list of actions and
descriptions that enable selective activation. See also checkpoint
6.3.
- Using MSAA
[MSAA] on the Windows platform:
- Retrieve the node in the document object that has current focus.
- Call the
IHTMLDocument4::fireEvent
method on that node.
Related techniques
- See image map techniques.
References
- For information on how to register event handlers through the DOM, and
dispatch events properly, refer to
Section 1.3 Event listener registration in "Document Object Model (DOM)
Level 2 Events Specification" [DOM2EVENTS].
- For example,
section 16.5 of the SVG 1.0 Candidate Recommendation [SVG] specifies
processing order for user interface events.
-
Ensure that every message (e.g., prompt, alert,
notification, etc.) that is a non-text element and is part of the
user agent user interface
has a text equivalent.
Note: For example, if the user is alerted of an event by an
audio cue, a visually-rendered text equivalent in the status bar could satisfy
this checkpoint. Per checkpoint
6.5, a text equivalent for each such message must be available through an
API. See also
checkpoint 6.6 for
requirements for programmatic notification of changes to the user
interface.
Notes and rationale
- User agents should use modality-specific messages in the user interface
(e.g., graphical scroll bars, beeps, and flashes) as long as redundant
mechanisms are available or possible. These redundant mechanisms will benefit
all users, not just users with disabilities.
Who benefits
- Users with blindness, deafness, or who are hard of hearing. Mechanisms that
are redundant to audio will benefit individuals who are deaf, hard of hearing,
or operating the user agent in a noisy or silent environment where the use of
sound is not practical.
Example techniques
- Render text messages on the status bar of the graphical user interface.
Allow users to query the viewport for this status information (in addition to
having access through graphical rendering).
- Make available information in a manner that allows other software to
present it according to the user's preferences. For instance, if proportional
scroll bars are used in the graphical interface to indicate the position of the
viewport in content, make available this same information in text form. For
instance, this will allow other software to render the proportion of content
viewed as synthesized speech or as braille.
Doing more
- Allow configuration to render or not render status information (e.g., allow
the user to hide the status bar).
2.1 Render content according to
specification. (P1)
Checkpoint 2.1
- Render content
according to format specification (e.g., for a markup language or style sheet
language).
- Rendering requirements include format-defined interactions between author
preferences and user preferences/capabilities (e.g., when to render the
"
alt
" attribute in HTML, the rendering order of
nested OBJECT
elements in HTML, test attributes in SMIL, and the
cascade in CSS2).
- When a rendering requirement of another specification contradicts a
requirement of UAAG 1.0, the user agent may disregard the rendering requirement
of the other specification and still satisfy this checkpoint; see the section
on the relation of User Agent Accessibility Guidelines 1.0 to general software
design guidelines and other specifications. for more information.
- The user agent is not required to satisfy this checkpoint for all
implemented specifications; see the section on
conformance profiles for more information.
- This checkpoint excludes the requirements of checkpoint 2.6.
Note: If a conforming user agent does not render a content
type, it should allow the user to choose a way to handle that content (e.g., by
launching another application, by saving it to disk, etc.).
Notes and rationale
- Provision two of the checkpoint only applies when the rendering requirement
of another specification contradicts the requirements of the current document;
no exemption is granted if the other specification is consistent with or silent
about a requirement made by the current document.
Who benefits
- Users with disabilities when specifications include features that promote
accessibility (e.g., scalable graphics benefit users with low vision, style
sheets allow users to override author and user style sheets).
Example techniques
- Provide access to attribute values (one at a time, not as a group). For
instance, allow the user to select an element and read values for all
attributes set for that element. For many attributes, this type of inspection
should be significantly more usable than a view of the text source.
- When content changes dynamically (e.g., due to embedded scripts or
automatic content retrieval), users need to have access to the content before
and after the change.
- Make available information about abbreviation and acronym expansions. For
instance, in HTML, look for abbreviations specified by the ABBR and ACRONYM
elements. The expansion may be given with the "title" attribute (refer to the
Web Content Accessibility Guidelines 1.0 [WCAG10], checkpoint 4.2). To
provide expansion information, user agents may:
- Allow the user to configure that the expansions be used in place of the
abbreviations,
- Provide a list of all abbreviations in the document, with their expansions
(a generated glossary of sorts)
- Generate a link from an abbreviation to its expansion.
- Allow the user to query the expansion of a selected or input
abbreviation.
- If an acronym has no expansion in one location, look for another occurrence
in content that does. User agents may also look for possible expansions (e.g.,
in parentheses) in surrounding context, though that is a less reliable
technique.
Related techniques
- See the sections on access to content, link techniques, table
techniques, frame techniques, and form techniques.
Doing more
- If the requirements of the current document contradict the rendering
requirements of another specification, the user agent may offer a configuration
to allow conformance to one or the other specification.
References
- Sections 10.4 ("Client Error 4xx") and 10.5 ("Server Error 5xx") of the
HTTP/1.1 specification [RFC2616] state that user agents
should have the following behavior in case of these error conditions:
Except when responding to a HEAD request, the server SHOULD include an
entity containing an explanation of the error situation, and whether it is a
temporary or permanent condition. These status codes are applicable to any
request method. User agents SHOULD display any included entity to the user.
- For content
authored in text formats, provide a view of the text source. For the purposes of this
checkpoint, a text format is any media object given an Internet media type of
"text" (e.g., "text/plain", "text/html", or "text/*") as defined in RFC 2046
[RFC2046], section 4.1.
- A user agent satisfies this checkpoint by providing a source view for any
text format, not just implemented text formats.
- The user agent is only required to satisfy this checkpoint for text formats
that are part of a conformance claim; see the section on
conformance profiles for more information. However, user agents should
provide a text view for all implemented text formats.
Notes and rationale
- In general, user agent developers should not rely on a "source view" to
convey information to users, most of whom are not familiar with markup
languages. A source view is still important as a "last resort" to some users as
content might not otherwise be accessible at all.
Who benefits
- Users with blindness, low vision, deafness, hard of hearing, and any user
who requires the text source to understand the content.
Example techniques
- Make the text view useful. For instance, enable links (i.e.,
URIs), allowing searching and other navigation within the view.
- A source view is an easily-implementable view that will help users inspect
some types of content, such as style sheet fragments or scripts. This does not
mean, however, that a source view of style sheets is the best user
interface for reading or changing style sheets.
Doing more
- Even when an Internet media type is not available (e.g., for local files),
provide a text view for common text formats such as HTML and XHTML.
- Provide a source view for any text format, not just implemented text
formats.
- Allow
configuration to provide access to each piece of unrendered conditional content "C".
- When a specification does not explain
how to provide access to this content, do so as follows:
- If C is a summary, title, alternative, description, or expansion of another
piece of content D, provide access through at least one of the following
mechanisms:
- (1a) render C in place of D;
- (2a) render C in addition to D;
- (3a) provide access to C by allowing the user to query D. In this case, the
user agent must also alert the user, on a per-element
basis, to the existence of C (so that the user knows to query D);
- (4a) allow the user to follow a link to C from the context of D.
- Otherwise, provide access to C through at least one of the following
mechanisms:
- (1b) render a placeholder for C, and
allow the user to view the original author-supplied content associated with
each placeholder;
- (2b) provide access to C by query (e.g., allow the user to query an element
for its attributes). In this case, the user agent
must also alert the user, on a per-element basis, to the existence of C;
- (3b) allow the user to follow a link in context to C.
- To satisfy provision one of this checkpoint, the configuration may be a
switch that, for all content, turns on or off the access mechanisms described
in provision two.
- To satisfy provision two of this checkpoint, the user agent may provide
access on a per-element basis (e.g., by allowing the user to query individual
elements) or for all elements (e.g., by offering a configuration to render
conditional content all the time).
Note: For instance, an HTML user agent might allow users to
query each element for access to conditional content supplied for the
"alt
", "title
", and "longdesc
"
attributes. Or, the user agent might allow configuration so that the value of
the "alt
" attribute is rendered in place of all IMG
elements (while other conditional content might be made available through
another mechanism).
Notes and rationale
- There may be more than one piece of conditional content associated with
another piece of content (e.g., multiple captions tracks associated with the
visual track of a presentation).
- Note that the alert requirement of this checkpoint is per-element. A single
resource-level alert (e.g., "there is conditional content somewhere here") does
not satisfy the checkpoint, but may be part of a solution for satisfying this
checkpoint. For example, the user agent might indicate the presence of
conditional content "somewhere" with menu in the toolbar. The menu items could
provide both per-element alert and access to the content (e.g., by opening a
viewport with the conditional content rendered).
Who benefits
- Any user for whom the author has provided conditional content for
accessibility purposes. This includes: text equivalents for users with
blindness or low vision, or users who are deaf-blind, and captions, for users
who with deafness or who are hard of hearing.
Example techniques
- Allow users to choose more than one piece of conditional content at a given
time. For instance, users with low vision may want to view images (even
imperfectly) but require a text equivalent for
the image; the text may be rendered with a large font or as
synthesized speech.
- In HTML 4 [HTML4], conditional content
mechanisms include the following:
- Allow the user to
configure how the user agent renders a long description (e.g., "longdesc"
in HTML 4 [HTML4]). Some possibilities
include:
- Render the long description in a separate view.
- Render the long description in place of the associated element.
- Do not render the long description, but allow the user to query whether an
element has an associated long description (e.g., with a context-sensitive
menu) and provide access to it.
- Use an icon (with a text equivalent) to
indicate the presence of a long description.
- Use an audio cue to indicate the presence of a long description when the
user navigates to the element.
- For an object (e.g., an image) with an author-specified geometry that the
user agent does not render, allow the user to configure how the conditional
content should be rendered. For example, within the specified geometry, by
ignoring the specified geometry altogether, etc.
- For multimedia presentations with several alternative tracks, ensure access
to all tracks and allow the user to select individual tracks. (As an example,
the QuickTime player [QUICKTIME] allows users to turn
on and off any number of tracks separately.) For example, construct a list of
all available tracks from short descriptions provided by the author (e.g.,
through the "title" attribute).
- For multimedia presentations with several alternative tracks, allow users
to choose tracks based on natural language
preferences. SMIL 1.0
[SMIL] allows users to specify captions
in different natural languages. By setting language preferences in the SMIL
player (e.g., the G2 player [G2]), users may access captions (or
audio) in different languages. Allow users to specify different languages for
different content types (e.g., English audio and Spanish captions).
- If a multimedia presentation has several captions
(or subtitles) available, allow the user to choose from among them. Captions
might differ in level of detail, reading level, natural language, etc. Multilingual
audiences may wish to have captions in different natural languages on the screen at
the same time. Users may wish to use both captions and audio descriptions
concurrently as well.
- Make apparent through the user agent user
interface which audio tracks are meant to
be played separately (e.g., by allowing the user to select each one
independently from a menu).
-
Section 7.8.1 of SMIL 2.0 [SMIL20] defines the 'readIndex'
attribute, which specifies the position of the current element in the order in
which values of the
longdesc
, title
, and
alt
attributes are to be read aloud.
Related techniques
- See the section on access to content.
Doing more
- If the user agent satisfies the checkpoint by implementing 1b
(placeholders), allow the user to toggle back and forth between a placeholder
and the original author-supplied content. Some users with a cognitive
disability may find it difficult to access content after turning on rendering
of too many images (even when those images were turned on one by one). Sample
technique: allow the user to designate a placeholder and request to view the
associated content in a separate viewport (e.g., through a context menu), leaving the placeholder in context.
Allow the user to close the new viewport manually.
- Make information available with different levels of detail. For example,
for a voice browser, offer two options for
HTML
IMG
elements:
- Speak only "alt" text by default, but allow the user to hear "longdesc"
text on an image by image basis.
- Speak "alt" text and "longdesc" for all images.
- Allow the user to configure different natural language preferences for
different types of conditional
content (e.g., captions and audio descriptions). Users with disabilities
may need to choose the language they are most familiar with in order to
understand a presentation for which supplementary tracks are not all available
in all desired languages. In addition, some users may prefer to hear the
program audio in its original language while reading captions in another,
fulfilling the function of subtitles or to improve foreign language
comprehension. In classrooms, teachers may wish to configure the language of
various multimedia elements to achieve specific educational goals.
2.4 Allow time-independent interaction.
(P1)
Checkpoint 2.4
- For rendered content where user input is
only possible within a finite time interval controlled by the user agent, allow
configuration to provide a view where user
interaction is time-independent.
- The user agent may satisfy this checkpoint by pausing processing
automatically to allow for user input, and resuming processing on explicit user request. When
this technique is used, pause at the end of each time interval where user input
is possible. In the paused state:
- Alert the user that the rendered content has been paused
(e.g., highlight the pause button in a multimedia player's control panel).
- Highlight which enabled elements are
time-sensitive.
- Allow the user to interact with the enabled elements.
- Allow the user to resume on explicit user request (e.g., by
pressing the play button in a multimedia player's control panel; see also checkpoint 4.5).
- The user agent may satisfy this checkpoint by generating a
time-independent (or, "static") view, based on the original content, that offers the user the same
opportunities for interaction. The static view should reflect the structure and
flow of the original time-sensitive presentation; orientation cues will help
users understand the context for various interaction opportunities.
- When satisfying this checkpoint for a real-time presentation, the user
agent may discard packets that continue to arrive after the construction of the
time-independent view (e.g., when paused or after the construction of a static
view).
- This checkpoint does not apply when
the user agent cannot recognize
the time interval in the presentation format, or when the user agent cannot
control the timing (e.g., because it is controlled by the server).
Note: If the user agent satisfies this checkpoint by
pausing automatically, it may be necessary to pause more than once when there
are multiple opportunities for time-sensitive user interaction. When pausing,
pause synchronized content as well (whether rendered in the same or different
viewports) per checkpoint
2.6. In SMIL 1.0
[SMIL], for example, the "begin
", "end
",
and "dur
" attributes synchronize
presentation components. See also checkpoint 3.5, which involves client-driven content
retrieval.
Notes and rationale
- The user agent could satisfy this checkpoint by allowing the user to step
through an entire presentation manually (as one might advance frame by frame
through a movie). However, this is likely to be tedious and lead to information
loss, so the user agent should preserve as much of the flow and order of the
original presentation as possible.
- The requirement to pause at the end (rather than at the beginning)
of a time-interval is to allow the user to review content that may change
during the elapse of this time.
- The configuration option is important because techniques used to satisfy
this checkpoint may lead to information loss for some types of content (e.g.,
highly interactive real-time presentations).
- When different streams of time-sensitive content are not synchronized (and
rendered in the same or different viewports), the user agent is not required to
pause the pieces all at once. The assumption is that both streams of content
will be available at another time.
Who benefits
- Some users with a physical disability who may not have the time to interact
with the content, and users with
serial access to content or who navigate sequentially.
Example techniques
- Some HTML user agents recognize time intervals specified through the
META
element, although this usage is not defined in HTML 4 [HTML4].
- Render time-dependent links as a static list that occupies the same screen
real estate; authors may create such documents in SMIL 1.0 [SMIL]. Include
temporal context in the list of links. For example, provide the time at which
the link appeared along with a way to easily jump to that portion of the
presentation.
- For a presentation that is not "live", allow the user to choose from a menu
of available time-sensitive links (essentially making them
time-independent).
Doing more
- Provide a view where time intervals are lengthened, but not infinitely
(e.g., allow the user to multiple time intervals by 3, 5, and 10). Or, allow
the user to add extra time (e.g., 10 seconds) to each time interval.
- Allow the user to view a list of all media elements or links of the
presentations sorted by start or end time or alphabetically.
- Alert the user whenever pausing the user agent may lead to packet
loss.
References
- Refer to section
4.2.4 of SMIL 1.0
[SMIL] for information about the SMIL time model.
2.5 Make captions, transcripts, audio descriptions available. (P1)
Checkpoint 2.5
- Allow
configuration or control to render text transcripts, collated text transcripts,
captions, and audio descriptions in content at the same time as the associated audio tracks and
visual tracks.
Notes and rationale
- Users may wish to a read a transcript at the same time as a related visual
or audio track and pause the visual or audio track while reading; see checkpoint 4.5.
Who benefits
- Users with blindness or low vision (audio descriptions and text captions,
etc.) and users with deafness or who are hard of hearing.
Example techniques
- Allow users to turn on and off audio descriptions and captions.
- For the purpose of applying this clause, SMIL 1.0 [SMIL] user agents should recognize
as captions any media object whose reference from SMIL is guarded by the
'
system-captions
' test attribute.
- SMIL user agents should allow users to configure whether they want to view
captions, and this user interface switch should be bound to the
'
system-captions
' test attribute. Users should be able to indicate
a preference for receiving available audio descriptions. Note:
SMIL 1.0
[SMIL] does not include a mechanism analogous to 'system-captions'
for audio descriptions, though [SMIL20] does, called
'systemAudioDesc'.
- Another SMIL 1.0 test attribute, '
system-overdub-or-captions
',
allows users to choose between subtitles and overdubs in multilingual
presentations. User agents should not interpret a value of
'caption
' for this test attribute as meaning that the user prefers
accessibility captions; that is the purpose of the
'system-captions
' test attribute. When subtitles and accessibility
captions are both available, users who are deaf may prefer to view captions, as
they generally contain information not in subtitles: information on music,
sound effects, who is speaking, etc.
- User agents that play QuickTime movies should allow the user to turn on and
off the different tracks embedded in the movie. Authors may use these
alternative tracks to provide content for accessibility purposes. The Apple
QuickTime player provides this feature through the menu item "Enable
Tracks."
- User agents that play Microsoft Windows Media Object presentations should
provide support for Synchronized Accessible Media Interchange (SAMI [SAMI]), a protocol
for creating and displaying captions) and should allow users to configure how
captions are viewed. In addition, user agents that play Microsoft Windows Media
Object presentations should allow users to turn on and off other conditional content, including
audio description and alternative
visual tracks.
References
- Developers implementing SMIL 1.0 [SMIL] should consult "Accessibility
Features of SMIL" [SMIL-ACCESS].
2.6 Respect synchronization cues.
(P1)
Checkpoint 2.6
- Respect
synchronization cues (e.g., in markup) during rendering.
Notes and rationale
- The term "synchronization cues" refers to pieces of information that may
affect synchronization, such as the size and expected duration of tracks and
their segments, the type of element and how much those elements can be sped up
or slowed down (both from technological and intelligibility standpoints).
- Captions and audio descriptions may not make
sense unless rendered synchronously with related video or audio content. For
instance, if someone with a hearing disability is watching a video presentation
and reading associated captions, the captions should be
synchronized with the audio so that the individual can use any residual
hearing. For audio descriptions, it is crucial that an audio
track and an audio description track be synchronized to avoid having them
both play at once, which would reduce the clarity of the presentation.
Who benefits
- Users with deafness or who are hard of hearing (e.g., for audio
descriptions and audio tracks), and some users with a cognitive
disability.
Example techniques
- For synchronization in SMIL 2.0 [SMIL20], refer to section
10, the timing and synchronization module.
- The idea of "sensible time-coordination" of components in the definition of
synchronize centers on the idea of
simultaneity of presentation, but also encompasses strategies for handling
deviations from simultaneity resulting from a variety of causes. Consider how
deviations might be handled for captions for a multimedia
presentation such as a movie clip. Captions consist of a text equivalent of the
audio track that is synchronized with the
visual track. Typically, a segment of the captions appears visually near
the video for several seconds while the person reads the text. As the visual
track continues, a new segment of the captions is presented. However, a problem
arises if the captions are longer than can fit in the display space. This can
be particularly difficult if due to a visual disability, the font size has been
enlarged, thus reducing the amount of rendered caption text that can be
presented. The user agent needs to respond sensibly to such problems, for
example by ensuring that the user has the opportunity to navigate (e.g., scroll
down or page down) through the caption segment before proceeding with the next
segment of the visual track.
- Developers of user agents need to determine how they will handle other
synchronization challenges, such as:
- Under what circumstances will the presentation automatically pause? Some
circumstances where this might occur include:
- the segment of rendered caption text is more than can fit on the visual
display
- the user wishes more time to read captions or the collated text
transcript
- the audio description is of longer duration than the natural pause in the
audio.
- Once the presentation has paused, then under what circumstances will it
resume (e.g., only when the user signals it to resume, or based on a predefined
pause length)?
- If the user agent allows the user to jump to a location in a presentation
by activating a link, then how will related tracks behave? Will they jump as
well? Will the user be able to return to a previous location or undo the
action?
-
Allow configuration to generate repair text when the user agent recognizes that the author has failed to
provide conditional content that was
required by the format specification.
- The user agent may satisfy this checkpoint by basing the repair text on any
of the following available sources of information: URI reference, content type,
or element type. Note, however, that additional information that would enable
more helpful repair might be available but not "near" the missing conditional
content. For instance, instead of generating repair text on a simple URI
reference, the user agent might look for helpful information near a different
instance of the URI reference in the same document object, or might retrieve
useful information (e.g., a title) from the resource designated by the URI
reference.
Note: Some markup languages (such as HTML 4 [HTML4] and SMIL
1.0 [SMIL]
require the author to provide conditional content for some elements (e.g., the
"alt
" attribute on the IMG
element).
Notes and rationale
- Following are some examples of conditional content that is required by
format specification:
- In HTML 4
[HTML4], "
alt
" is required for the IMG
and
AREA
elements (for validation). (In SMIL 1.0 [SMIL], on the other
hand, "alt
" is not required on media objects.)
- Whatever the format, text equivalents for non-text content are required by
the Web Content Accessibility Guidelines 1.0 [WCAG10].
- Conditional content may come from markup, inside images (e.g., refer to
"Describing and retrieving photos using RDF and HTTP"
[PHOTO-RDF]), etc.
Who benefits
- Users with blindness or low vision.
Example techniques
- When HTTP is used, HTTP headers provide information about the URI of the Web resource ("Content-Location") and
its type ("Content-Type"). Refer to the HTTP/1.1 specification [RFC2616],
sections 14.14 and 14.17, respectively. Refer to "Uniform Resource Identifiers
(URI): Generic Syntax" ([RFC2396], section 4) for
information about URI references, as well as the HTTP/1.1 specification
[RFC2616],
section 3.2.1.
- An image or another piece of content may appear several times in content.
If one instance has associated conditional content but others do not, reuse
what the author did provide.
- Repair content may be part of another piece of content. For instance, some
image formats allow authors to store metadata there; refer to "Describing and
retrieving photos using RDF and HTTP" [PHOTO-RDF].
Related techniques
- See content repair techniques, and cell header repair strategies.
Doing more
- When configured per provision one of this checkpoint, inform the user
(e.g., in the generated text itself) that this content was not provided by the
author.
- Use heuristics based on the specification format. For instance, if the
alt
attribute is missing on the IMG
element in HTML,
but the title
attribute is present, base the repair content on the
title.
References
- The "Altifier Tool" [ALTIFIER] illustrates smart
techniques for generating text equivalents (for
images, etc.) when the author has not specified any.
- Additional repair techniques may be available from W3C's Evaluation and Repair Tools Working
Group.
- Allow at
least two configurations for when the user agent recognizes that conditional content required by
the format specification is present but
empty content:
Note: In some authoring scenarios,
empty content (e.g., alt=""
in HTML) may make an appropriate
text equivalent, such as when non-text content has no other
function than pure decoration, or when an image is part of a "mosaic" of
several images and does not make sense out of the mosaic. Refer to the Web
Content Accessibility Guidelines 1.0 [WCAG10] for more information about
text equivalents.
Notes and rationale
- User agents should render nothing in this case because the author may
specify an empty text equivalent for content that
has no function in the page other than as decoration.
Who benefits
- Users with blindness or low vision.
Example techniques
- The user agent should not render generic labels such as "[INLINE]" or
"[GRAPHIC]" for empty conditional
content (unless configured to do so).
- If no captioning information is available and captioning is turned on,
render "No captioning information available" in the captioning region of the
viewport (unless configured not to generate repair content).
Doing more
- Labels (e.g., "[INLINE]" or "[GRAPHIC]") may be useful in some situations,
so the user agent may allow configuration to render "No author text" (or
similar) instead of empty conditional content.
2.9 Render conditional
content automatically. (P3)
Checkpoint 2.9
- Allow
configuration to render all conditional content
automatically.
- As part of satisfying
provision one of this checkpoint, provide access according to specification, or
where unspecified, by applying one of the techniques 1a, 2a, or 1b defined in
checkpoint 2.3.
- The user agent is not required to render all conditional content at the
same time in a single viewport.
- Conformance detail: For all
content.
Note: For instance, an HTML user agent might allow
configuration so that the value of the "alt
" attribute is rendered in place of all
IMG
elements (while other conditional content might be made
available through another mechanism). The user agent may offer multiple
configurations (e.g., a first configuration to render one type of conditional
content automatically, a second to render another type, etc.).
Who benefits
- Users who have difficulties with navigation and manual access to content,
including some users with a physical disability and users with blindness or low
vision.
Example techniques
- Provide a "conditional content view", where all content that is not
rendered by default is rendered in place of associated content. For example,
Amaya
[AMAYA] offers a "Show alternate" view that accomplishes this. Note,
however, cases where an element has more than one piece of associated
conditional content (e.g., render them all as a list, or as a list of links,
etc.). For long conditional content, instead of rendering in place, link to the
content.
2.10 Don't render unsupported language.
(P3)
Checkpoint 2.10
- Allow
configuration not to render text in
unsupported scripts (i.e., writing systems) when that text
would otherwise be rendered.
- When configured per provision one
of this checkpoint, indicate to the user in context that author-supplied
content has not been rendered.
- This checkpoint does not require the user agent to allow different
configurations for different natural languages.
Note: This checkpoint is designed primarily to benefit
users with serial access to content or who navigate sequentially, allowing
them to skip portions of content that would be unusable if rendered as
"garbage".
Notes and rationale
- A script is a means of supporting the visual rendering of content in a
particular natural language. So, for user agents that render content visually,
a user agent might not recognize "the Cyrillic script", which would mean that
it would not support the visual rendering of Russian, Ukrainian, and other
languages that employ Cyrillic when written.
- There may be cases when a conforming user agent supports a natural language
but a speech synthesizer does not, or vice versa.
Who benefits
- Users with serial access to content or who navigate sequentially.
Example techniques
- Use a text substitute or accessible graphical icon to indicate that content
in a particular language has not been rendered. For instance, a user agent that
does not support Korean (e.g., does not have the appropriate fonts or voice
set) should allow configuration to announce the language change with the
message "Unsupported language – unable to render" (e.g., when the
language itself is not recognized) or "Korean not supported – unable to
render" (e.g., when the language is recognized by the user agent does not have
resources to render it). The user should also be able to choose no alert of
language changes. Rendering could involve speaking in the designated natural
language in the case of a voice browser or screen reader. If the natural
language is not supported, the language change alert could be spoken in the
default language by a screen reader or
voice browser.
- A user agent may not be able to render all characters in a document
meaningfully, for instance, because the user agent lacks a suitable font, a
character has a value that may not be expressed in the user agent's internal
character encoding, etc. In this case,
section 5.4 of HTML 4 [HTML4] recommends the following for
undisplayable characters:
- Adopt a clearly visible (or audible), but unobtrusive mechanism to alert
the user of missing resources.
- If missing characters are presented using their numeric representation, use
the hexadecimal (not decimal) form since this is the form used in character set
standards.
- When HTTP is used, HTTP headers provide information about content encoding
("Content-Encoding") and content language ("Content-Language"). Refer to the
HTTP/1.1 specification [RFC2616], sections 14.11 and
14.12, respectively.
- CSS2's attribute selector may be used with the HTML "lang" or XML
"xml:lang" attributes to control rendering based on
recognized natural language information. Refer also to the ':lang'
pseudo-class ([CSS2], section 5.11.4).
Related techniques
- See techniques for generated content,
which may be used to insert text to indicate a language
change.
- See content repair techniques and accessibility and internationalization
techniques.
- See techniques for synthesized
speech.
References
- For information on language codes, refer to "Codes for the representation
of names of languages" [ISO639].
- Refer to "Character Model for the World Wide Web" [CHARMOD]. It
contains basic definitions and models, specifications to be used by other
specifications or directly by implementations, and explanatory material. In
particular, this document addresses early uniform normalization, string
identity matching, string indexing, and conventions for URIs.
In addition to the techniques below, refer also to the section on user control of style.
- Allow
configuration not to render background image
content.
- The user agent may satisfy this checkpoint with a configuration to not
render any images, including background images. However, user agents
should satisfy this checkpoint by allowing users to turn off background images
alone, independent of other types of images in
content.
- This checkpoint must be satisfied for all
implemented image specifications; see the section on
conformance profiles.
- When configured not to render background images, the user agent is not
required to retrieve them until the user requests them explicitly. When
background images are not rendered, user agents should render a solid
background color instead; see checkpoint 4.3 for information about text colors.
- This checkpoint only requires control of background images for "two-layered
renderings", i.e., one rendered background image with all other content
rendered "above it".
- Conformance
profile labels:
Image.
Note: When background images are not rendered, they are
considered conditional
content. See checkpoint
2.3 for information about providing access to conditional content.
Notes and rationale
- This checkpoint does not address issues of multi-layered renderings and
does not require the user agent to change background rendering for multi-layer
renderings (refer, for example, to the 'z-index' property in Cascading Style
Sheets, level 2 ([CSS2], section 9.9.1).
Who benefits
- Some users with a cognitive disability or color deficiencies who may find
it difficult or impossible to read superimposed text or understand other
superimposed content.
Example techniques
- If background images are turned off, make available to the user associated
conditional content.
- In CSS, background images may be turned on/off with the
'background' and 'background-image' properties ([CSS2], section 14.2.1).
Doing more
- Allow control of image depth in multi-layer presentations.
3.2
Toggle audio, video, animated images. (P1)
Checkpoint 3.2
- Allow
configuration not to render audio, video, or animated image content, except on explicit user request.
- The user agent may satisfy this checkpoint by making video and animated
images invisible and audio silent, but this technique is not
recommended.
- This configuration is required for content rendered without any user
interaction (including content rendered on load or as the result of a script),
as well as content rendered as the result of user interaction that is not an explicit user request (e.g.,
when the user activates a link).
- This checkpoint must be satisfied for all
implemented audio, video, and animated image specifications; see the
section on
conformance profiles.
- When configured not to render audio, video, or animated images except on
explicit user request, the user agent is not required to retrieve them until
the user requests them explicitly.
- Conformance
profile labels:
Animation,
Video,
Audio.
Note: See
guideline 4 for additional requirements related to the control of rendered
audio, video, and animated images. When these content types are not rendered,
they are considered conditional
content. See checkpoint
2.3 for information about providing access to conditional content.
Who benefits
- Some users with a cognitive disability, for whom an excess of visual
information (and in particular animated information) might make it impossible
to understand parts of content. Also, audio rendered automatically on load may
interfere with speech synthesizers.
Example techniques:
- For user agents that hand off content to different rendering engines, the
configuration should cause the content not to be handed off, and instead a
placeholder rendered.
- The "silent" or "invisible" solution for satisfying this checkpoint (e.g.,
by implementing the
'visibility' property defined in section 11.2 of CSS 2 [CSS2]) is not
recommended. This solution means that the content is processed, though not
rendered, and processing may cause undesirable side effects such as firing
events. Or, processing may interfere with the processing of other content
(e.g., silent audio may interfere with other sources of sound such as the
output of a speech synthesizer). This technique should be deployed with
caution.
- As a placeholder for an animated image, render a motionless image built
from the first frame of the animated image.
3.3
Toggle animated or blinking text. (P1)
Checkpoint 3.3
- Allow
configuration to render animated or blinking text content as motionless, unblinking text.
Blinking text is text whose visual rendering alternates between visible and
invisible, at any rate of change.
- In this configuration, the user must still have access to the same text
content, but the user agent may render it in a separate viewport (e.g., for
large amounts of streaming text).
- The user agent may satisfy this checkpoint by always
rendering animated or blinking text as motionless, unblinking text.
Note: Animation (a rendering effect) differs from streaming
(a delivery mechanism). Streaming content might be rendered as an animation
(e.g., an animated stock ticker or vertically scrolling text) or as static text
(e.g., movie subtitles, which are rendered for a limited time, but do not give
the impression of movement).
Notes and rationale
- The definition of blinking text is based on the CSS2 definition of the
'blink' value; refer to [CSS2], section 16.3.1.
Who benefits
- Users with photosensitive epilepsy (for whom flashing content may trigger
seizures) and users with some cognitive disorders (for whom the distraction may
make the content unusable). Blinking text can also affect screen reader users,
since screen readers (in conjunction with speech synthesizers or braille
displays) may re-render the text every time it blinks.
- Configuration is preferred as some users may benefit from blinking effects
(e.g., users who are deaf or hard of hearing). However, the priority of this
checkpoint was assigned on the basis of requirements unrelated to this
benefit.
Example techniques
- The user agent may render the motionless text in a number of ways. Inline
is preferred, but for extremely long text, it may be better to render the text
in another viewport, easily reachable from the user's browsing context.
- Allow the user to turn off animated or blinking text through the user agent user interface
(e.g., by pressing the Escape key to stop animations).
- Some sources of blinking and moving text are:
- The BLINK element in HTML. The BLINK element is not defined by a W3C
specification.
- The MARQUEE element in HTML. The MARQUEE element is not defined by a W3C
specification.
- The 'blink' value of the
'text-decoration' property in CSS ([CSS2], section 16.3.1).
- In JavaScript, to control the start and speed of scrolling for a
MARQUEE
element:
document.all.myBanner.start();
document.all.myBanner.scrollDelay = 100
-
Allow configuration not to execute any executable
content (e.g., scripts and
applets).
Note: Scripts and applets may provide very useful
functionality, not all of which causes accessibility problems. Developers
should not consider that the user's ability to turn off scripts is an effective
way to improve content accessibility; turning off scripts means losing the
benefits they offer. Instead, developers should provide users with finer
control over user agent or content behavior known to raise accessibility
barriers. The user should only have to turn off scripts as a last resort.
Notes and rationale
- Executable content includes scripts, applets,
ActiveX controls, etc. This checkpoint does not apply to plug-ins; they are not part of content.
- Executable content includes those that run "on load" (e.g., when a document
loads into a viewport) and when other events occur (e.g., user interface
events).
- Where possible, authors should encode knowledge in a declarative manner
(i.e., through static definitions and expressions) rather than in scripts.
Knowledge and behaviors embedded in scripts can be difficult or impossible to
extract, which means that user agents are less likely to be able to offer
control by the user over the script's effect. For instance, with SVG animation
(see chapter
19 of SVG 1.0
[SVG]), one can create animation effects in a declarative manner,
using recognizable elements and attributes.
Who benefits
- Some users with photosensitive epilepsy; flickering or flashing,
particularly in the 4 to 59 flashes per second (hertz) range, may trigger
seizures. Peak sensitivity to flickering or flashing occurs at 20 hertz. Some
executable content can cause the screen to flicker.
Example techniques
- Some user agents allow users to turn off scripts in the "Security" part of
the user interface. Since some users seeking accessibility features may not
think to look there, include the on/off switch in an accessibility part of the
user interface as well. Also, include a "How to turn off scripts" entry in the
documentation index.
Related techniques
- See the section on script techniques.
Doing more
- When support for scripts is turned on, and when the user agent recognizes
that there are script alternatives available (e.g.,
NOSCRIPT
in
HTML), alert the user to the presence of the alternative (and make it easily
available). If a user cannot access the script content, the alert will raise
the user's awareness of the alternative, which may be more accessible.
- While this checkpoint only requires an on/off configuration switch, user
agents should allow finer control over executable content. For instance, in
addition to the switch, allow users to turn off just input device event
handlers, or to turn on and off scripts in a given scripting language
only.
3.5 Toggle automatic content retrieval.
(P1)
Checkpoint 3.5
- Allow
configuration so that the user agent only retrieves content on
explicit user request.
- When the user chooses not to retrieve (fresh) content, the user agent may
ignore that content; buffering is not required.
- The user agent is not required to satisfy this checkpoint for "client-side
redirects", i.e., author-specified instructions that a piece of content is
temporary and intermediate, and is replaced by content that results from a
second request. Authors (and Webmasters) should use the redirect mechanisms of
HTTP instead of client-side redirects.
- This checkpoint only applies when the user agent (not the server)
automatically initiates the request for fresh content.
Note: For example, if an HTML author has used a
META
element for automatic content retrieval, allow configuration to
override the automatic behavior with manual confirmation.
Notes and rationale
- Some HTML authors specify automatic content retrieval
using a META element with http-equiv="refresh", with the frequency specified by
the "content" attribute (seconds between retrievals).
Who benefits
- Some users with a cognitive disability, users with blindness or low vision,
and any user who may be disoriented (or simply annoyed) by automatically
changing content.
Example techniques
- Alert the user that suppressing the retrieval may lead to loss of
information (e.g., packet loss).
Doing more
- When configured not to retrieve content automatically, alert the user of
the frequency of retrievals specified in content, and allow the user to
retrieve fresh content manually (e.g., by following a link or confirming a
prompt).
- Allow users to specify their own retrieval frequency.
- Allow at least one configuration for low-frequency retrieval (e.g., every
10 minutes).
- Retrieve new content without displaying it automatically. Allow the user to
view the differences (e.g., by highlighting or filtering) between the currently
rendered content and the new content (including no differences).
- Allow configuration so that a client-side
redirect only changes content on explicit user request. This
configuration need not apply to client-side redirects specified to occur
instantaneously (i.e., after no delay). Client-side redirects may disorient the
user, but are less serious than automatic content retrieval since the
intermediate state (just before the redirect) is generally not important
content that the user might regret missing. Some HTML user
agents support client-side redirects authored using a
META
element
with http-equiv="refresh"
. This use of META
is not a
normative part of any W3C Recommendation and may pose interoperability
problems.
- Provide a configuration so that when the user navigates "back" through the
user agent history to a page with a client-side redirect, the user agent does
not re-execute the client-side redirect.
References
- For Web content authors: refer to the HTTP/1.1 specification [RFC2616] for
information about using server-side redirect mechanisms (instead of client-side
redirects).
-
Allow configuration not to render image content.
- The user agent may satisfy this checkpoint by making images invisible, but this technique is
not recommended.
Note: When images are not rendered, they are considered conditional content. See checkpoint 2.3 for
information about providing access to conditional content.
Notes and rationale
- This priority of
checkpoint 3.2 is higher than the priority of this checkpoint because an
excess of moving visual information is likely to be more distracting to some
users than an excess of still visual information.
Who benefits
- Some users with a cognitive disability, for whom an excess of visual
information might make it difficult to understand parts of content.
Related techniques
- See techniques for checkpoint 3.1.
Checkpoints:
4.1, 4.2, 4.3,
4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 4.14
In addition to the techniques below, refer also to the section on user control of style.
- Allow global configuration of the
scale of visually rendered text content.
Preserve distinctions in the size of rendered text as the user increases or
decreases the scale.
- As part of satisfying provision one of
this checkpoint, provide a configuration option to override
rendered text sizes specified by the author or user agent defaults.
- As part of satisfying provision one of
this checkpoint, offer a range of text sizes to the user that includes at
least:
- the range offered by the conventional utility available in the operating environment that
allows users to choose the text size (e.g., the font size), or
- if no such utility is available, the range of text sizes supported by the
conventional APIs of the
operating environment for drawing text.
- The user agent may satisfy provision one of this checkpoint through a
number of mechanisms, including zoom, magnification, and allowing the user to
configure a reference size for rendered text (e.g., render text at 36 points
unless otherwise specified). For example, for CSS2 [CSS2] user agents, the 'medium'
value of the 'font-size' property corresponds to a reference size.
- The word "scale" is used in this checkpoint to mean the general size of
text.
- The user agent is not required to satisfy this requirement through
proportional scaling. What must hold is that if rendered text A is smaller than
rendered text B at one value of this configuration setting, then text A will
still be smaller than text B at another value of this configuration
setting.
- Conformance
profile labels:
VisualText.
Notes and rationale
- For example, allow the user to configure the user agent to apply the same
font family across Web resources, so that all text is
displayed by default using that font family. Or, allow the user to control the
text scale dynamically for a given element, e.g., by navigating to the element
and zooming in on it.
- The choice of optimal techniques depends in part on which markup language
is being used. For instance, HTML user agents may allow the user to change the
font size of a particular piece of text (e.g., by using CSS user
style sheets) independent of other content (e.g., images). Since the user agent
can reflow the text after resizing the font, the rendered text will become more
legible without, for example, distorting bitmap images. On the other hand, some
languages, such as SVG, do not allow text reflow, which means that changes to
font size may cause rendered text to overlap with other content, reducing
accessibility. SVG is designed to scale, making a zoom functionality the more
natural technique for SVG user agents satisfying this checkpoint.
- The primary intention of this checkpoint is to allow users with low vision
to increase the size of text. Full configurability includes the choice of very
small text sizes that may be available, though this is not considered by the
User Agent Accessibility Guidelines Working Group to be part of the priority 1
requirement. This checkpoint does not include a "lower bound" (above which text
sizes would be required) because of how users' needs may vary across writing
systems and hardware.
Who benefits
- Users with low vision, who benefit from the ability to increase the text
scale. Note that some users may also benefit from the ability to choose small
font sizes (e.g., users of screen readers who wish to have more content per
screen so they have to scroll less frequently). People who use captions may
need to change the text scale.
Example techniques
- Inherit text size information from user preferences specified for the operating environment.
- Use operating
environment magnification features.
- The ratios of the sizes should be compressed at large text sizes, as the
same number of different sizes must be packed into a smaller dynamic
range.
- Vectorial formats such as Scalable Vector Graphics specification [SVG] are designed to
scale. For bitmap fonts, the user agent may need to round off font sizes when
the user increases or decreases the scale.
- Implement the
'font-size' property in CSS ([CSS2], section 15.2.4).
- In Windows, the
ChooseFont
function in the Comdlg32 library
creates the conventional utility that allows users to choose text (font) size.
The DrawText
API is the lower-level API for drawing text.
Doing more
- Allow the user to configure the text size on an element level (i.e., more
precisely than globally). User style sheets allow such detailed
configurations.
- Allow the user to configure the text size differently for different scripts (i.e., writing systems).
- Allow global configuration of the font
family of all visually rendered text
content.
- As part of satisfying provision one of
this checkpoint, provide a configuration option to override
font families specified by the author or by user agent defaults.
- As part of satisfying provision one of
this checkpoint, offer a range of font families to the user that includes at
least:
- the range offered by the conventional utility available in the operating environment that
allows users to choose the font family, or
- if no such utility is available, the range of font families supported by
the conventional APIs of the
operating environment for drawing text.
- For text that cannot be rendered properly using the
user's preferred font family, the user agent may substitute an alternative font
family.
Note: For example, allow the user to specify that all text is to be rendered in a particular
sans-serif font family.
Who benefits
- Users with low vision or some users with a cognitive disability or reading
disorder. Some people require the ability to change the font family of text in
order to read it. People who use captions may also need to change the font
family.
Example techniques
- Inherit font family information from user preferences specified for the operating environment.
- Implement the
'font-family' property in CSS ([CSS2], section 15.2.2).
- Allow the user to override author-specified font families with differing
levels of detail. For instance, use font A in place of any sans-serif font and
font B in place of any serif font.
- In Windows, the
ChooseFont
function in the Comdlg32 library
creates the conventional utility that allows users to choose font
families.
Doing more
- Allow the user to configure font families on an element level (i.e., more
precisely than globally). User style sheets allow such detailed
configurations.
- Allow global configuration of the
foreground and background color of all visually
rendered text content.
- As part of satisfying provision one of
this checkpoint, provide a configuration option to override
foreground and background colors specified by the author or user agent
defaults.
- As part of satisfying provision one of
this checkpoint, offer a range of colors to the user that includes at least:
- the range offered by the conventional utility available in the operating environment that
allows users to choose colors, or
- if no such utility is available, the range of colors supported by the
conventional APIs of the
operating environment for specifying colors.
Note: User configuration of foreground and background
colors may inadvertently lead to the inability to distinguish ordinary text
from selected text, focused text, etc. See checkpoint 10.2 for more
information about highlight styles.
Who benefits
- Users with color deficiencies and some users with a cognitive disability.
People who use captions may need to change the text color.
Example techniques
- Inherit foreground and background color information from user preferences
specified for the operating
environment.
- Implement the
'color' and
'border-color' properties in CSS 2 ([CSS2], sections 14.1 and 8.5.2,
respectively).
- Implement the
'background-color' property (and other background properties) in CSS 2
([CSS2],
section 14.2.1).
- SMIL does not have a global property for "background color", but allows
specification of background color by region (refer, for example, to the
definition of the '
background-color
' attribute defined in section 3.3.1 of
SMIL 1.0
[SMIL]). In the case of SMIL, the user agent would satisfy this
checkpoint by applying the user's preferred background color to all regions
(and to all root-layout
elements as well). SMIL 1.0 does not have
a way to specify the foreground color of text, so that portion of the
checkpoint would not apply.
- In SVG 1.0
[SVG] the fill
(section 11.3) and
stroke (section 11.4) properties are used to paint foreground colors.
- In Windows, the
ChooseColor
function in the Comdlg32 library
creates the conventional utility that allows users to choose colors.
Doing more
- Allow the user to specify minimal contrast between foreground and
background colors, adjusting colors dynamically to meet those
requirements.
- Allow the user to slow the presentation rate
of rendered audio and animation content (including
video and animated images).
- As part of satisfying provision one of this
checkpoint, for a visual track, provide at
least one setting between 40% and 60% of the original speed.
- As part of satisfying provision one of this
checkpoint, for a prerecorded audio track including audio-only presentations,
provide at least one setting between 75% and 80% of the original speed.
- When the user agent allows the user to slow
the visual track of a synchronized multimedia presentation to between 100% and
80% of its original speed, synchronize the visual and audio tracks (per checkpoint 2.6). Below 80%,
the user agent is not required to render the audio
track.
- The user agent is not required to satisfy this checkpoint for audio and
animations whose recognized role is to create a purely
stylistic effect. Purely stylistic effects include background sounds,
decorative animated images, and effects caused by style sheets.
- Conformance
profile labels:
Animation,
Audio.
Note: The style exception of this checkpoint is based on
the assumption that authors have satisfied the requirements of the "Web Content
Accessibility Guidelines 1.0" [WCAG10] not to convey information
through style alone (e.g., through color alone or style sheets alone).
Notes and rationale
- Slowing one track (e.g., video) may make it harder for a user to understand
another synchronized track (e.g., audio), but if the user can understand
content after two passes, this is better than not being able to understand it
at all.
- Some formats (e.g., streaming formats) might not enable the user agent to
slow down playback and would thus be subject to applicability.
Who benefits
- Some users with a learning or cognitive disability, or some users with
newly acquired sensory limitations (such as a person who is newly blind and
learning to use a screen reader). Users who have beginning familiarity with a
natural language may also
benefit.
Example techniques
- When changing the rate of audio, avoid pitch distortion.
- HTML 4 [HTML4], background animations may
be specified with the deprecated
background
attribute.
- The
SMIL 2.0 Time Manipulations Module ([SMIL20], chapter 11) defines the
speed
attribute, which can be used to change the playback rate (as
well as forward or reverse direction) of any animation.
- Authors sometimes specify background sounds with the "bgsound" attribute.
Note: This attribute is not part of HTML 4 [HTML4].
Doing more
- Allowing the user to speed up audio is also useful. For example, some users
with serial access to content or who navigate sequentially benefit
from the ability to speed up audio.
- Provide the same functionality for audio and animations whose recognized role is to create a purely
stylistic effect.
References
- Refer to variable playback speed techniques used for Digital Talking Books
[TALKINGBOOKS].
4.5 Start, stop, pause, and navigate
multimedia. (P1)
Checkpoint 4.5
- Allow the user to stop, pause, and resume
rendered audio and animation content (including video and
animated images) that last three or more seconds at their default playback
rate.
- Allow the user to navigate efficiently
within audio and animations (including video and animated
images) that last three or more seconds at their default playback rate.
- The user agent may satisfy the navigation requirement of provision two of
this checkpoint through forward and backward
serial access techniques (e.g., advance five seconds), or direct access
techniques (e.g., play starting at the 10-minute mark), or some
combination.
- When serial access techniques are used to
satisfy provision two of this checkpoint, the user agent is not required to
play back content during advance or rewind (though doing so may help orient the
user).
- When the user pauses a real-time audio or animation, the user agent may
discard packets that continue to arrive during the pause.
- This checkpoint applies to content that is either rendered automatically
(e.g., on load) or on explicit request from the user.
- The user agent is not required to satisfy this checkpoint for audio and
animations whose recognized role is to create a purely
stylistic effect; see checkpoint
4.4 for more information about what constitutes a stylistic effect.
- Conformance
profile labels:
Animation,
Audio.
Note: The lower bound of three seconds is part of this
checkpoint since control is not required for brief audio and animation clips,
beeps, etc. Respect synchronization cues per checkpoint 2.6.
Notes and rationale
- Some formats (e.g., streaming formats), might not enable the user agent to
fast forward or rewind content and would thus be subject to applicability.
- For some streaming media formats, the user agent might not be able to offer
some functionalities (e.g,. fast forward) when the content is being delivered
over the Web in real time. However, the user agent is expected to offer these
functionalities for content (in the same format) that is fully available, for
example on the user's computer.
- Playback during serial advance or rewind
is not required. For example, the user agent is not required to play an
animation at double speed during a continuous fast forward. Similarly, when the
user fast forwards or rewinds an animation, the user agent is not required to
play back a synchronized audio track.
Who benefits
- Some users with a cognitive disability.
Example techniques
- Serial access and sequential navigation
techniques include, for example, rewind in large or small time increments,
forward to the next audio track, etc. Direct access techniques include access
to visual track number 7, to the 10-minute mark, etc. The best choice of
serial, sequential, or direct access techniques will depend on the nature of
the content being rendered.
- If buttons are used to control advance and rewind, make the advance/rewind
distances proportional to the time the user activates the button. After a
certain delay, accelerate the advance/rewind.
- The
SMIL 2.0 Time Manipulations Module ([SMIL20], chapter 11) defines the
speed
attribute, which can be used to change the playback
direction (forward or reverse) of any animation. See also the
accelerate
and decelerate
attributes.
- Some content lends itself to different forward and reverse functionalities.
For instance, compact disk players often let listeners fast forward and rewind,
but also skip to the next or previous song.
Doing more
- Allow fine control over advance and rewind functionalities. Some users with
a physical disability will find useful the ability to advance or rewind the
presentation in (configurable) increments.
- The user agent should display time codes or represent otherwise position in
content to orient the user.
- Apply techniques for changing audio speed without introducing
distortion.
- Alert the user whenever pausing the user agent may lead to packet
loss.
- Provide the same functionality for audio and animations whose recognized role is to create a purely
stylistic effect.
- Allow users to insert temporal bookmarks in presentation; Home Page Reader
[HPR]
provides this feature.
References
- Refer to fast forward and rewind techniques used for Digital Talking Books
[TALKINGBOOKS].
- For
graphical viewports, allow configuration so that captions
synchronized with a visual track in content
are not obscured by it.
- Render captions "on top" of the visual track and, as part of satisfying checkpoint 4.3, allow the
user to configure the foreground and background color of the rendered captions
text.
- Render captions and video in separate
viewports.
Notes and rationale
- Rendering captions in a separate viewport may make it easier for users with
screen readers to access the captions.
- Traditionally, captions text is rendered with a solid background color.
Research shows that some users prefer white lettering above a black
background.
Who benefits
- Some users with a cognitive disability or with color deficiencies, who may
need to configure rendering to make captions more legible.
Example techniques
- For the purpose of applying this clause, SMIL 1.0 [SMIL] and SMIL 2.0 [SMIL20] user
agents should recognize as captions any media object whose reference from SMIL
is affected by the '
system-captions
' test attribute.
Doing more
- Allow the user to turn off rendering of captions.
- Allow users to position captions. Some users (e.g., users with low vision
and a hearing disability (or who are not fluent in the language of an audio
track) may need captions and video to have a particular spatial relation to
each other, even if this results in partially obscured content. Positioning
techniques include the following:
- User agents should implement the positioning features of the employed
markup or style sheet language. Even when a markup language does not specify a
positioning mechanism, when a user agent can recognize distinct text transcripts, collated text transcripts,
or captions, the user agent should allow the
user to reposition them. User agents are not expected to allow repositioning
when the captions, etc., cannot be separated from other media (e.g., the
captions are part of the visual track).
- Implement the CSS 2
'position' property ([CSS2], section 9.3.1).
- Allow the user to choose whether captions appear at the bottom or top of
the video area or in other positions. Currently authors may place captions
overlying the video or in a separate box. Captions prevent users from being
able to view other information in the video or on other parts of the screen,
making it necessary to move the captions in order to view all content at once.
In addition, some users will find captions easier to read if they can place
them in a location best suited to their reading style.
- Allow users to configure a general preference for caption position and to
be able to fine-tune specific cases. For example, the user may want the
captions to be in front of and below the rest of the presentation.
- Allow the user to drag and drop the captions to a place on the screen. To
ensure device-independence, allow the user to enter the screen coordinates of
one corner of the caption.
- Do not require users to edit the source code of the presentation to achieve
the desired effect.
- Allow the user to position all parts of a presentation rather than trying
to identify captions specifically (i.e., solving the problem generally may be
easier than for captions alone).
- Allow global configuration of the
volume of all rendered audio, with an option to override
audio volumes specified by the author or user agent defaults.
- As part of satisfying provision one
of this checkpoint, allow the user to choose zero volume (i.e., silent).
Note: User agents should allow configuration of volume
through available operating
environment mechanisms.
Example techniques
- Use audio control mechanisms provided by the operating environment. Control
of volume mix is particularly important, and the user agent should provide easy
access to those mechanisms provided by the operating environment.
- Implement the CSS 2
'volume' property ([CSS2], section 19.2).
- Implement the
'display',
'play-during', and
'speak' properties in CSS 2 ([CSS2], sections 9.2.5, 19.6, and
19.5, respectively).
- Authors sometimes specify background sounds with the "bgsound" attribute.
Note: This attribute is not part of HTML 4 [HTML4].
Who benefits
- Users who are hard of hearing or who rely on audio and synthesized speech
rendering. Users in a noisy environment will also benefit.
References
- Refer to guidelines for audio characteristics used for Digital Talking
Books
[TALKINGBOOKS].
- Allow independent control of the volumes of rendered audio content synchronized to play
simultaneously.
- The user control required by this checkpoint includes the ability to override author-specified volumes for the
relevant sources of audio.
- The user agent is not required to satisfy this checkpoint for audio whose
recognized role is to create a purely
stylistic effect; see checkpoint
4.4 for more information about what constitutes a stylistic effect.
- Conformance
profile labels:
Audio.
Note: The user agent should satisfy this checkpoint by
allowing the user to control independently the volumes of all audio sources (e.g., by implementing a general
audio mixer type of functionality). See checkpoint 4.10 for information about controlling the volume
of synthesized speech.
Notes and rationale
- Sounds that play at different times are distinguishable and therefore
independent control of their volumes is not required by this checkpoint (since
volume control required by checkpoint 4.7 suffices).
- There are at least three good reasons for strongly recommending that the
volume of all audio sources be independently configurable, not just those
synchronized to play simultaneously:
- Sounds that are not synchronized may end up playing simultaneously.
- If the user cannot anticipate when a sound will play, the user cannot
adjust the global volume control at appropriate times to affect this
sound.
- It is extremely inconvenient to have to adjust the global volume
frequently.
- Sounds specified by the author to play "on document load" are likely to
overlap with each other. If they continue to play, they are also likely to
overlap with subsequent sounds played manually or automatically.
Who benefits
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech rendering.
Related techniques
- For each source of audio, allow the user to control the volume
using the same user interface used to satisfy the requirements of checkpoint 4.5.
Doing more
- Provide the same functionality for audio whose
recognized role is to create a purely stylistic effect.
See also techniques for synthesized speech
rendering.
4.9 Configure synthesized speech rate.
(P1)
Checkpoint 4.9
- Allow
configuration of the synthesized speech rate, according to the full range
offered by the speech synthesizer.
Note: The range of synthesized speech rates offered by the
speech synthesizer may depend on natural language.
Example techniques
- For example, many speech synthesizers offer a range for English speech of
120 - 500 words per minute or more. The user should be able to increase or
decrease the rendering rate in convenient increments (e.g., in large steps,
then in small steps for finer control).
- User agents may allow different synthesized speech rate configurations for
different natural languages. For example, this may be implemented with CSS2
style sheets using the :lang
pseudo-class ([CSS2], section 5.11.4).
- Use synthesized speech mechanisms provided by the operating environment.
- Implement the CSS 2
'speech-rate' property ([CSS2], section 19.8).
Who benefits
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech rendering.
Doing more
- Content may include commands that are interpreted by a speech synthesizer
to change the rate (or control other synthesized speech parameters). This
checkpoint does not require the user agent to allow the user to override
author-specified rate changes (e.g., by transforming or otherwise stripping out
these commands before passing on the content to the speech synthesizer). Speech
synthesizers themselves may allow user override of author-specified rate
changes. For these such synthesizers, the user agent should ensure access to
this feature.
4.10 Configure synthesized speech volume.
(P1)
Checkpoint 4.10
- Allow control of
the synthesized speech volume, independent of other sources of audio.
Note: See checkpoint 4.8 for information about independent volume
control of different sources of audio.
Example techniques
- The user agent should allow the user to make synthesized speech louder and
softer than other audio sources.
- Use synthesized speech mechanisms provided by the operating environment.
- Implement the CSS 2
'volume' property ([CSS2], section 19.2).
Who benefits
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech rendering.
4.11 Configure
synthesized speech characteristics. (P1)
Checkpoint 4.11
- Allow configuration of synthesized speech
characteristics according to the full range of values offered by the speech
synthesizer.
Note: Some speech synthesizers allow users to choose values
for synthesized speech characteristics at a higher abstraction layer, i.e., by
choosing from present options that group several characteristics. Some typical
options one might encounter include: "voice ("adult male voice", "female child
voice", "robot voice", etc.), "pitch", "stress", etc. Ranges for values may
vary among speech synthesizers.
Example techniques
- Use synthesized speech mechanisms provided by the operating environment.
- One example of a synthesized speech
API is Microsoft's Speech Application Programming Interface [SAPI].
-
Who benefits
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech rendering.
References
- For information about these synthesized speech characteristics, refer to
descriptions in section 19.8 of Cascading Style Sheets Level 2 [CSS2].
4.12 Specific synthesized speech characteristics. (P2)
Checkpoint 4.12
- Allow
configuration of synthesized speech pitch. Pitch refers to the average
frequency of the speaking voice.
- Allow
configuration of synthesized speech pitch range. Pitch range specifies a
variation in average frequency.
- Allow
configuration of synthesized speech stress. Stress refers to the height of
"local peaks" in the intonation contour of the voice.
- Allow
configuration of synthesized speech richness. Richness refers to the
richness or brightness of the voice.
Note: This checkpoint is more specific than checkpoint
4.11. It requires support for the voice characteristics listed in the
provisions of this checkpoint. Definitions for these characteristics are based
on descriptions in section 19 of the Cascading Style Sheets Level 2
Recommendation
[CSS2]; refer to that specification for additional informative descriptions. Some speech
synthesizers allow users to choose values for synthesized speech
characteristics at a higher abstraction layer, i.e., by choosing from present
options distinguished by "gender", "age", "accent", etc. Ranges of values may
vary among speech synthesizers.
Who benefits
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech rendering. Some users with a hearing disability as well may
require control over these parameters.
Related techniques
- See the techniques for checkpoint 4.11.
4.13 Configure synthesized speech features.
(P2)
Checkpoint 4.13
- Provide support
for user-defined extensions to the synthesized speech dictionary.
- Provide support
for spell-out: where text is spelled one character at a time, or according to
language-dependent pronunciation rules.
- Allow at least two configurations for speaking numerals: one
where numerals are spoken as individual digits, and one where full numbers are
spoken.
- Allow at least two configurations for speaking punctuation:
one where punctuation is spoken literally, and one where punctuation is
rendered as natural pauses.
Note: Definitions for the functionalities listed in the
provisions of this checkpoint are based on descriptions in section 19 of the
Cascading Style Sheets Level 2 Recommendation [CSS2]; refer to that specification
for additional informative descriptions.
Example techniques
-
Who benefits
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech rendering.
References
- For information about these functionalities, refer to descriptions in
section 19.8 of Cascading Style Sheets Level 2 [CSS2].
- Allow the user to choose from and apply
alternative author style sheets (such as linked
style sheets).
- Allow the user to choose from and apply
at least one user style sheet.
- Allow the user to turn off (i.e.,
ignore) author and user style sheets.
- This checkpoint only applies to user agents that support
style sheets.
Note: By definition, the user agent's default style
sheet is always present, but may be overridden by author or user styles.
Developers should not consider that the user's ability to turn off author and
user style sheets is an effective way to improve content accessibility; turning
off style sheet support means losing the many benefits they offer. Instead,
developers should provide users with finer control over user agent or content
behavior known to raise accessibility barriers. The user should only have to
turn off author and user style sheets as a last resort.
Example techniques
- For HTML [HTML4], make available "class" and
"id" information so that users can override styles.
- Implement user style sheets.
- Implement the
"!important" semantics of CSS 2 ([CSS2], section 6.4.2).
Who benefits
- Any user with a disability who needs to override the author's style sheets
or user agent default style sheets in order to have control over style and
presentation, or who needs to tailor the style of rendered content to meet
their own needs.
Doing more
- Allowing the user to select more than one style sheet may be a useful way
to implement other requirements of this document. Also, if the user agent
offers several default style sheets, the user agent can also use these to
satisfy some requirements. By making available alternative style sheets on the
Web, people can thus improve the accessibility of deployed user agents.
- Inform the user (e.g., through a discreet flag in the user interface) when
alternate author style sheets are available. Allow the user to easily choose
from among them.
References
-
Chapter 7 of the CSS1 Recommendation [CSS1] recommends that the user be
able to specify user style sheets, and that the user be able to turn off
individual style sheets.
- For information about how alternative style sheets are specified in HTML 4
[HTML4],
refer to
section 14.3.1.
- For information about how alternative style sheets are specified in XML 1.0
[XML], refer
to "Associating Style Sheets with XML documents Version 1.0"
[XMLSTYLE].
5.1 No automatic content focus change.
(P2)
Checkpoint 5.1
- Allow
configuration so that if a viewport opens without explicit user request, neither
its content focus nor its user interface focus
automatically becomes the current focus.
- To satisfy provision one of this checkpoint, configuration is preferred,
but is not required if the content focus can only ever be moved on explicit user request.
Who benefits
- Some users with a cognitive disability, blindness, or low vision, who may
be disoriented if the focus moves automatically (and unexpectedly) to a new
viewport. These users may also find it difficult to restore the previous point
of regard.
Example techniques
- Allow the user to configure how the
current focus changes when a new viewport opens. For instance, the user
might choose between these two options:
- Do not change the focus when a viewport opens, but alert the user (e.g.,
with a beep, flash, and text message on the status bar). Allow the user to
navigate directly to the new window upon demand.
- Change the focus when a window opens and use a subtle alert (e.g., a beep,
flash, and text message on the status bar) to indicate that
the focus has changed.
- If a new viewport or prompt appears but focus does
not move to it, alert assistive technologies (per checkpoint 6.6) so that they
may discreetly inform the user.
- When a viewport is duplicated, the focus in the new viewport should
initially be the same as the focus in the original viewport. Duplicate
viewports allow users to navigate content (e.g., in search of some information)
in one viewport while allowing the user to return with little effort to the
point of regard in the duplicate viewport. There are other techniques for
accomplishing this (e.g., "registers" in Emacs).
- In JavaScript, the focus may be changed with
myWindow.focus();
- For user agents that implement CSS 2 [CSS2], the following rule will
generate a message to the user at the beginning of link text for links that are
meant to open new windows when followed:
A[target=_blank]:before
{ content:"Open new window" }
Doing more
- The user agent may also allow configuration about whether the pointing
device moves automatically to windows that open without an explicit user
request.
- For graphical user interfaces, allow configuration so that the viewport with the
current focus remains "on top" of all
other viewports with which it overlaps.
Notes and rationale
- In most operating environments, the viewport with focus is generally the
viewport "on top". In some environments, it's possible to allow a viewport that
is not on top to have focus.
Who benefits
- Some users with a cognitive disability, who may find it disorienting if the
viewport being viewed unexpectedly changes.
Doing more
- The user agent may also allow configuration about whether the viewport
designated by the pointing device always remains on top.
- When configured to keep the viewport with current focus on top, discreetly
alert the user when another viewport opens.
- Allow
configuration so that viewports only open on explicit user request.
- When configured per provision one of this
checkpoint, instead of opening a viewport automatically, alert the user and
allow the user to open it with an explicit request (e.g., by
confirming a prompt or following a link generated by the user agent).
- Allow the user to close viewports.
- To satisfy provision one of this checkpoint, configuration is preferred,
but is not required if viewports can only ever open on explicit user request.
- If a viewport (e.g., a frame set) contains other viewports, these
requirements only apply to the outermost container viewport.
- User creation of a new viewport (e.g., empty or with a new resource loaded)
through the user agent's user interface constitutes an explicit user
request.
Note: Generally, viewports open automatically as the result
of instructions in content. See also checkpoint 5.1 (for
control over changes of focus when a viewport opens) and checkpoint 6.6 (for
programmatic notification of changes to the user interface).
Who benefits
- Some users with serial access to content
or who navigate sequentially, who may
find navigation of multiple open viewports difficult. Also, some users with a
cognitive disability may be disoriented by multiple open viewports.
Example techniques
- For HTML [HTML4], allow the user to control
the process of opening a document in a new "target" frame or a viewport created
by a script. For example, for
target="_blank"
, open the window
according to the user's preference.
- For SMIL
[SMIL], allow the user to control viewports created with the
"
new
" value of the "show
" attribute.
- In JavaScript, windows may be opened with:
myWindow.open("example.com", "My New Window");
myWindow.showHelp(URI);
Doing more
- Allow configuration to prompt the
user to confirm (or cancel) closing any viewport that starts to close without
explicit user request. For
instance, in JavaScript, windows may be closed with
myWindow.close();
. Some users with a cognitive disability may find it
disorienting if a viewport closes automatically. On the other hand, some users
with a physical disability may wish these same viewports to close automatically
(rather than being required to close them manually).
5.4 Selection and focus in viewport.
(P2)
Checkpoint 5.4
- Ensure that when a viewport's selection or
content focus changes, it is at least partially in the viewport after the change.
Note: For example, if users navigating links move to a
portion of the document outside a graphical viewport, the viewport should
scroll to include the new location of the focus. Or, for users of audio
viewports, allow configuration to render the selection or focus immediately
after the change.
Who benefits
- Users who may be disoriented by a change in focus or selection that is not
reflected in the viewport. This includes some users with blindness or low
vision, and some users with a cognitive disability.
Example techniques
- There are times when the content focus changes (e.g., link navigation) and
the viewport should track it. There are other times when the viewport changes
position (e.g., scrolling) and the content focus should follow it. In either
case, the focus (or selection) should be in the viewport after the change.
- If a search causes the selection or focus to change, ensure that the found
content is not hidden by the search prompt.
- When the content focus changes, register the newly focused element in the
navigation sequence; sequential
navigation should start from there.
- Unless viewports have been coordinated, changes to selection or focus in
one viewport should not affect the selection or focus in another viewport.
- The persistence of the selection or focus in the viewport will vary
according to the type of viewport. For any viewport with persistent rendering
(e.g., a two-dimensional graphical or tactile
viewport), the focus or selection should remain in the viewport after the
change until the user changes the viewport. For any viewport without persistent
rendering (e.g., an audio viewport), once the focus or selection has been
rendered, it will no longer be "in" the viewport. In a pure audio environment,
the whole persistent context is in the mind of the user. In a graphical
viewport, there is a large shared buffer of dialog information in the display.
In audio, there is no such sensible patch of interaction that is maintained by
the computer and accessed, at will, by the user. The audio rendering of content
requires the elapse of time, which is a scarce resource. Consequently, the flow
of content through the viewport has to be managed more carefully, notably when
the content was designed primarily for graphical rendering.
- If the rendered selection or focus does not fit entirely within the limits
of a graphical viewport, then:
- if the region actually displayed prior to the change was within the
selection or focus, do not move the viewport.
- otherwise, if the region actually displayed prior to the change was not
within the newly selected or focused content, move to display at least the
initial fragment of such content.
- Allow
configuration to prompt the user to confirm (or cancel) any
form submission.
- Configuration is preferred, but it not required if forms can only ever be
submitted on explicit user request.
Note: Examples of automatic form submission include:
script-driven submission when the user changes the state of a particular form
control associated with the form (e.g., via the pointing device), submission
when all fields of a form have been filled out, and submission when a
"mouseover" or "change" event
occurs.
Notes and rationale
- Many user agents offer this configuration as a security feature.
Example techniques
- In HTML 4
[HTML4], form submit controls are the
INPUT element (section 17.4) with
type="submit"
and
type="image"
, and the
BUTTON element (section 17.5) with type="submit"
.
- Allow the user to configure script-based submission (e.g., form submission
accomplished through an "onChange" event). For instance, allow these settings:
- Do not allow script-based submission.
- Allow script-based submission after confirmation from the user.
- Allow script-based submission without prompting the user (but not by
default).
- Authors may write scripts that submit a form when particular
events occur (e.g., "onchange" events). Be watchful for this type of code,
which may disorient users:
<SELECT NAME="condition" onchange="switchpage(this)">
As soon as the user attempts to navigate the menu, the "switchpage" function
opens a document in a new viewport. Try to avoid orientation problems that may
be caused by scripts bound to form elements.
- Be aware that users may inadvertently pressing the Return or
Enter key and accidentally submit a form.
- In JavaScript, a form may be submitted with:
document.form[0].submit();
document.all.mySubmitButton.click();
- Generate a form submit button when the author has not provided one.
Who benefits
- Any user who might be disoriented by an automatic form submission (e.g.,
users who navigate
sequentially through select box options, or some users with a cognitive
disability) or who might inadvertently submit a form (e.g., some users with a
physical disability).
Doing more
- Some users may not want to have to confirm all form submissions, so allow
multiple configurations, such as: confirm all form submissions; confirm
script-activated form submissions; confirm all form submissions except those
done through the graphical user interface (e.g., when the user moves content focus to a submit button and
activates it).
- Users with serial access to content or who navigate sequentially may think
that the submit button in a form is the "final" user interface control they
need to complete before submitting the form. Therefore, for forms in which
additional controls follow a submit button, if those controls have not been
completed, inform the user and ask for confirmation (or completion) before
submission.
- For forms, allow users to search for user interface
controls that need to be changed by the user before submitting the
form.
6.1 Programmatic access to HTML/XML
infoset. (P1)
Checkpoint 6.1
-
Provide programmatic read access to XML content by making available
all of the information items defined by the W3C XML Infoset
[INFOSET].
-
Provide programmatic read access to HTML content by making available all of the
following information items defined by the W3C XML Infoset
[INFOSET]:
- Document Information item: children, document element, base URI,
charset
- Element Information items: element-type name, children, attributes,
parent
- Attribute Information items: attribute-type name, normalized value,
specified, attribute type, references, owner element
- Character Information items: character code, parent element
- Comment Information items: content, parent
-
If the user can modify HTML and XML content ("write access") through the
user interface (e.g., through form controls), allow for the same
modifications programmatically.
Notes and rationale
- The primary reason for requiring user agents to provide access to the
Infoset is that this gives assistive technologies access to the original
structure of the document. For example, this means that assistive technologies
that render content as synthesized speech are not required to construct the
speech view by "reverse engineering" a graphical view. Direct access to the
structure allows the assistive technologies to render content in a manner best
suited to a particular output device. This does not mean that assistive
technologies should be prevented from having access to the rendering of the
conforming user agent; rather, that they not be required to depend entirely on
it. In fact, user agents the render as synthesized speech may wish to
synchronize a graphical view with a speech view; see checkpoint 6.4 for
information about access to some rendered information.
- Allowing assistive technologies write access to the Infoset allows them to:
- modify the attribute list of a document and thus add information into the
document object that will not be rendered by the user agent.
- add entire nodes to the document that are specific to the assistive
technologies and that may not be rendered by a user agent unaware of their
function.
- The ability to write to the Infoset can improve performance for the
assistive technology. For example, if an assistive technology has already
traversed a portion of the document object and knows that a section (e.g., a
style element) could not be rendered, it can mark this section "to be
skipped".
- Another benefit of write access is to add information necessary for audio
rendering but that would not be stored directly in the document object during
parsing (e.g., numbers in an ordered list). An assistive technology component
can add numeric information to the document object. The assistive technology
can also mark a subtree as having been traversed and updated, to eliminate
recalculating the information the next time the user visits the subtree.
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
6.2 DOM access to HTML/XML content. (P1)
Checkpoint 6.2
-
Provide access to the content required in checkpoint 6.1 by conforming to the following modules of the
W3C Document Object Model DOM
Level 2 Core Specification [DOM2CORE] and exporting bindings
for the interfaces they define:
- for HTML: the Core module.
- for XML: the Core and XML modules.
-
As part of satisfying provision one of this checkpoint,
- Export the normative bindings specified in the DOM Level 2 Core
Specification [DOM2CORE] (namely, for Java
[JAVA] and ECMAScript
[ECMASCRIPT] operating environments).
- For other environments, the bindings exported to satisfy provision one of
this checkpoint (e.g., C++ bindings) must be publicly documented.
- The user agent is not required to export the bindings outside of the user
agent process (though doing so may be useful to assistive technology
developers).
Note: Refer to the "Document Object Model (DOM) Level 2
Core Specification" [DOM2CORE] for information about
HTML and XML versions covered. This
checkpoint is stands apart from
checkpoint 6.1 to emphasize the distinction between what information is
required and how to provide access to that information.
Notes and rationale
- Provide programmatic read (and write) access to the document object in a
thread-safe manner, to ensure that the application and system are not
compromised. In multi-threaded environments, assistive technologies will access
the document object (in or out of process) on a separate thread. Simultaneous
access to the document object on more than one thread could result in deadlock
situations and memory access violations, corrupting the application and
possibly the assistive technology. Developers should therefore use commonly
available operating system supported interprocess communication features (such
as semaphores) to ensure synchronized, thread-safe access.
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
Example techniques
- When generating repair content, user
agents should try to ensure consistency after repair between the
document object and the rendering structure (see checkpoint 6.4).
Related techniques
- See the appendix on loading assistive technologies
for DOM access.
References
- For information about rapid access to Internet Explorer's [IE-WIN] DOM
through COM, refer to Browser Helper Objects [BHO].
- Refer to the DirectDOM Java implementation of the DOM
[DIRECTDOM].
- For information about communication with Mozilla's Gecko rendering engine
on the Windows platform, refer to [GECKO-API].
- The Open Directory Project [ODP-DOM] features a listing of
DOM implementations.
6.3 Programmatic access to
non-HTML/XML content. (P1)
Checkpoint 6.3
- For content
other than HTML and XML, provide
structured programmatic read access to content,
and write access to those parts of content that the user can modify through the
user interface.
- As part of satisfying provision one of
this checkpoint, implement at least one
API according to this API cascade:
- The API is defined by a W3C Recommendation, or the API is
publicly documented and designed to enable interoperability with assistive
technologies.
- If no such API is available, or if available APIs do not enable the user
agent to satisfy the requirements,
- "Structured programmatic access" means access through an API to recognized
information items of the content (such as the information items of the XML
Infoset
[INFOSET]). Plain text has little structure, so an API that provides
access to it will be correspondingly less complex than an API for XML content.
For content more structured than plain text, an API that only provides access
to a stream of characters does not satisfy the requirement of providing
structured programmatic access. This document does not otherwise define what is
sufficiently structured access.
- An API is considered "available" if the specification of the API is
published (e.g., as a W3C Recommendation) in time for integration into a user
agent's development cycle.
Note: This checkpoint addresses content not covered by checkpoint 6.1 and checkpoint 6.2.
Notes and rationale
- Some examples of markup languages covered by this checkpoint include
SGML
applications other than HTML and
RTF, and TeX.
- Some software (e.g., Microsoft Word and Excel for Windows) offer APIs
specific to their formats.
- Some source information (e.g., schemas or style sheets) may be processed
but not appear in the document object.
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
Example techniques
- In Windows, the
DrawText
API is the lower-level API for
drawing text.
Related techniques
- See techniques for checkpoint
6.5.
References
- Some public APIs that enable access include:
- Microsoft Active Accessibility ([MSAA]) in Windows 95/98/NT
versions.
- Sun Microsystems Java Accessibility API ([JAVAAPI]) in Java JDK. If the
user agent supports Java applets and provides a Java Virtual Machine to run
them, the user agent should support the proper loading and operation of a Java
native assistive technology. This assistive technology can provide access to
the applet as defined by Java accessibility standards.
- The ATK library
[ATK] provides a set of interfaces for accessibility in the GNOME
environment.
- Adobe implements the MSAA interface for access to PDF content [ADOBE].
6.4
Programmatic access to information about rendered content. (P1)
Checkpoint 6.4
- For graphical user agents, make
available bounding dimensions and coordinates of rendered graphical objects.
Coordinates must be relative to the point of origin in the graphical
environment (e.g., with respect to the desktop), not the viewport.
- For graphical user agents, provide
access to the following information about each piece of rendered text: font
family, font size, and foreground and background colors.
- As part of satisfying provisions one
and two of this checkpoint, implement at least one API according to the API
cascade described in provision two of checkpoint 6.3.
Note: User agents should provide programmatic access to
additional useful information about rendered content that is not available
through the APIs required by checkpoints 6.2 and
6.3, including the correspondence (in both directions) between graphical
objects and their source in the document object, and information
about the role of each graphical object.
Notes and rationale
- The first two provisions of this checkpoint refer to what is actually
rendered on the screen. In CSS for example, this means "actual values"
rather than "computed values". Note, however, that the CSS module of the
DOM) Level 2 Style Specification
[DOM2STYLE] does not provide access to actual values, only read-only
access to computed values.
- This document requires programmatic access to rendering structure (even in
the absence of standard APIs) for at least the following reasons:
- Some user agents (e.g,. screen magnifiers) are more interested in what is
rendered than the document object, so access to the document object may not be
helpful.
- A graphical user agent knows what information is available on the screen.
Assistive technologies should not be required to recalculate what's on the
screen because the work has already been done.
- The user agent's rendering is definitive. If an assistive technology is
required to build a rendering structure from the same document object, style
sheets, and user preferences, that rendering is unlikely to match exactly the
user agent's own rendering.
- HTML content on the Web may be invalid. Some user agents generate rendering
structure based on content that is different from what appears in the document
object after repair. Thus, there can be a mismatch between what's on the screen
and what's available through the DOM.
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
References
- For font information Microsoft Windows, see the
ITextFont interface.
- For font informationa when using [ATK], see the AtkText
interface.
- For font informationa when using the Java Accessibility API [JAVAAPI], see
the
AccessibleComponent interface.
6.5 Programmatic operation of user agent
user interface. (P1)
Checkpoint 6.5
-
Provide programmatic read access to user agent user interface
controls, selection,
content focus, and user interface
focus.
-
Provide programmatic write access for those user agent user interface
controls that the user can modify through the user interface.
-
As part of satisfying provisions one and two of this checkpoint, implement
at least one API according to the API cascade described in provision two of checkpoint 6.3.
Note: APIs used to satisfy the requirements of this
checkpoint may be independent of a particular operating environment (e.g., the
W3C DOM), conventional APIs for a particular operating environment,
conventional APIs for programming languages, plug-ins,
virtual machine environments, etc. User agent developers are encouraged to
implement APIs that allow assistive technologies to interoperate with multiple
types of software in a given operating environment (user agents, word
processors, spreadsheet programs, etc.), as this reuse will benefit users and
assistive technology developers. User agents should always follow operating
environment conventions for the use of input and output APIs.
Notes and rationale
- It is important to use APIs that ensure that text content is
available to assistive technologies as text and not, for example, as a series
of strokes drawn on the screen.
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
Example techniques
- Use conventional user interface
controls. Third-party assistive technology developers are more likely able to
access conventional controls than
custom controls. If you use custom controls, review them for accessibility and
compatibility with third-party assistive technology. Ensure that they provide
accessibility information through an API as is done for the conventional
controls.
- Make use of operating
environment-level features. See the appendix of
accessibility features for some common operating systems.
- Operating system and application frameworks have conventions for
communication with input devices. In the case of Windows, OS/2, the X Windows
System, and Mac OS, the window manager provides graphical user interface
(GUI) applications with this information through the
messaging queue. In the case of non-GUI applications, the compiler run-time
libraries provide conventional mechanisms for receiving keyboard input in the
case of desktop operating systems. If you use an application framework such as
the Microsoft Foundation Classes, the framework used should support the same
conventional input mechanisms.
- Do not communicate directly with an input device; this may circumvent operating environment
messaging. For instance, in Windows, do not open the keyboard device driver
directly. It is often the case that the windowing system needs to change the
form and method for processing conventional input mechanisms for proper
application coexistence within the user interface framework.
- Do not implement your own input device event queue mechanism; this may
circumvent operating environment messaging. Some assistive technologies use
conventional system facilities for simulating keyboard and mouse events. From
the application's perspective, these events are no different than those
generated by the user's actions. The "Journal Playback Hooks" (in both OS/2 and
Windows) are one example of an application that feeds the standard event
queues. For an example of a standard event queue mechanism, refer to the
"Carbon Event Manager Preliminary API Reference" [APPLE-HI].
- Operating environments have
conventions for communicating with output devices. In the case of common
desktop operating systems such as Windows, OS/2, and Mac OS, conventional APIs are
provided for writing to the display and the multimedia subsystems.
- Avoid rendering text in the form of a bitmap before transferring
to the screen, since some screen readers rely on the user agent's offscreen
model. An offscreen model is rendered content created by an
assistive technology that is based on the rendered content of another user
agent. Assistive technologies that rely on an offscreen model generally
construct it by intercepting conventional operating environment drawing
calls. For example, in the case of display drivers, some screen readers are
designed to monitor what is drawn on the screen by capturing drawing calls at
different points in the drawing process. While knowing about the user agent's
formatting may provide some useful information to assistive technologies, this
document encourages assistive technologies to access to content directly
through published APIs (such as the DOM) rather than via a particular
rendering.
- Common operating environment two-dimensional graphics engines and drawing
libraries provide functions for drawing text to the
screen. Examples of this are the Graphics Device Interface (GDI) for Windows,
Graphics Programming Interface (GPI) for OS/2, and the X library (XLIB) for the
X Windows System or Motif.
- Do not communicate directly with an output device.
- Do not draw directly to the video frame buffer.
- Do not provide your own mechanism for generating predefined operating environment
sounds.
- When writing textual information in a GUI operating environment, use
conventional operating environment
APIs for drawing text.
- Use operating
environment resources for rendering audio information. When doing so, do
not take exclusive control of system audio resources. This could prevent an
assistive technology such as a screen reader from speaking if they use software
text-to-synthesized speech conversion. Also, in operating environments like
Windows, a set of audio sound resources is provided to support conventional
sounds such as auditory alerts. These preset sounds are
used to trigger SoundSentry graphical cues when a
problem occurs; this benefits users with hearing disabilities. These cues may
be manifested by flashing the desktop, active caption bar, or current viewport.
Thus, it is important to use the conventional mechanisms to generate audio
feedback so that operating environments or special assistive technologies can
add additional functionality for users with hearing disabilities.
- API designers should promote backwards compatibility so that assistive
technologies do not suddenly break when a new version of an API is published
and implemented by user agents.
References
- Some public accessibility APIs include:
- Microsoft Active Accessibility ([MSAA]). This the conventional
accessibility API for the Windows 95/98/NT operating systems. See, for example,
information about the
Iaccessible interface.
- Sun Microsystems Java Accessibility API ([JAVAAPI]) in the Java JDK. This
is the conventional accessibility API for the Java environment. If the user
agent supports Java applets and provides a Java Virtual Machine to run them,
the user agent should support the proper loading and operation of a Java native
assistive technology. This assistive technology can provide access to the
applet as defined by Java accessibility standards.
- For information about rapid access to Internet Explorer's [IE-WIN] DOM
through COM, refer to Browser Helper Objects [BHO].
- For information about communication with Mozilla's Gecko rendering engine
on the Windows platform, refer to [GECKO-API].
6.6 Programmatic notification of
changes. (P1)
Checkpoint 6.6
- Provide programmatic notification of
changes to content,
user agent user interface controls,
selection, content focus, and user interface focus.
- As part of satisfying provision one of
this checkpoint, implement at least one API according to the API cascade of
provision two of checkpoint
6.3.
Note: For instance, provide programmatic notification when
user interaction in one frame causes automatic changes to content in
another.
Who benefits
- Users with a disability who rely on assistive technologies for output.
Example techniques
- Write output to and take input from conventional operating environment
APIs rather than directly from hardware. This will enable the
input/output to be redirected from or to assistive technology devices –
for example, screen readers and braille displays often redirect output (or copy
it) to a serial port, while many devices provide character input, or mimic
mouse functionality. The use of generic APIs makes this feasible in a way that
allows for interoperability of the assistive technology with a range of
applications.
- Provide notification when an action in one frame causes the content of
another frame to change. Allow the user to navigate with little effort to the
frame(s) that changed.
Related techniques
- See techniques for checkpoint
6.5.
References
- For information on how to register event handlers through the DOM, and
dispatch events properly, refer to
Section 1.3 Event listener registration in "Document Object Model (DOM)
Level 2 Events Specification" [DOM2EVENTS].
Section 1.5.4 Mutation event types discusses notification of any changes to
the structure of a document.
- Refer also to information about monitoring HTML events
through the document object model in
Internet Explorer
[IE-WIN].
-
Implement
APIs for the keyboard as follows:
Note: An operating environment may define more than one
conventional API for the keyboard. For instance, for Japanese and Chinese,
input may be processed in two stages, with an API for each.
Who benefits
- Users with a disability who rely on assistive technologies for input.
Example techniques
- Account for author-specified keyboard bindings, such as those specified by
"accesskey" attribute in HTML 4 ([HTML4], section
17.11.2).
- Test that all user interface
components are operable by software or devices that emulate a keyboard. Use SerialKeys and/or voice recognition software to test
keyboard event emulation.
Related techniques
- Apply the techniques for checkpoint 1.1 to the keyboard.
Doing more
- Enhance the functionality of conventional operating environment controls to
improve accessibility where none is provided by responding to conventional
keyboard input mechanisms. For example provide keyboard navigation to menus and
dialog box controls in the Apple Macintosh operating system. Another example is
the Java Foundation Classes, where internal frames do not provide a keyboard
mechanism to give them focus. In this case, you will need to add keyboard
activation through the conventional keyboard activation facility for Abstract
Window Toolkit components.
- For an API implemented to satisfy
requirements of this document, support the character encodings required for
that API.
Note: Support for character encodings is important so that
text is not "broken" when communicated to assistive technologies. For example,
the DOM Level 2 Core Specification [DOM2CORE], section 1.1.5
requires that the DOMString
type be encoded using UTF-16.
Who benefits
- Users with disabilities who rely on assistive technologies for input and
output.
Example techniques
- The list of character encodings that any conforming implementation of Java
version 1.3
[JAVA13] must support is: US-ASCII, ISO-8859-1, UTF-8, UTF-16BE,
UTF-16LE, and UTF-16.
- MSAA [MSAA] relies on the
COM interface, which in turn relies on Unicode [UNICODE],
which means that for MSAA a user agent must support UTF-16. From Chapter 3 of
the COM documentation, on interfaces, entitled "Interface Binary Standard":
Finally, and quite significantly, all strings passed through all COM
interfaces (and, at least on Microsoft platforms, all COM APIs) are Unicode
strings. There simply is no other reasonable way to get interoperable objects
in the face of (i) location transparency, and (ii) a high-efficiency object
architecture that does not in all cases intervene system-provided code between
client and server. Further, this burden is in practice not large.
6.9 DOM access to CSS style sheets. (P2)
Checkpoint 6.9
-
For user agents that implement Cascading Style
Sheets (CSS), provide programmatic access to style sheets by
conforming to the CSS module of the W3C Document Object Model (DOM) Level 2 Style Specification
[DOM2STYLE] and exporting bindings for the interfaces it
defines.
-
As part of satisfying provision one of this checkpoint:
- Export the normative bindings specified in the CSS module of the
DOM) Level 2 Style Specification
[DOM2STYLE] (namely, for Java [JAVA] and
ECMAScript [ECMASCRIPT] operating
environments).
- For other environments, the bindings exported to satisfy provision one of
this checkpoint must be publicly documented.
- For the purposes of satisfying this checkpoint, Cascading Style Sheets
(CSS) are defined by either CSS Level 1
[CSS1] or CSS Level 2 [CSS2].
- The user agent is not required to export the bindings outside of the user
agent process.
Note: Refer to the "Document Object Model (DOM) Level 2
Style Specification" [DOM2STYLE] for information
about CSS versions covered.
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
- For APIs implemented to satisfy the
requirements of this document, ensure that programmatic exchanges proceed in a
timely manner.
Note: For example, the programmatic exchange of information
required by other checkpoints in this document should be efficient enough to
prevent information loss, a risk when changes to content or user interface
occur more quickly than the communication of those changes. Timely exchange is
also important for the proper synchronization of alternative renderings. The
techniques for this checkpoint explain how developers can reduce communication
delays. This will help ensure that assistive technologies have timely access to
the document object model and other
information that is important for providing access.
Notes and rationale
- This document requires that a conforming user agent provide access to
content and user interface information through APIs because assistive
technologies must be able to respond incrementally to changes in the user's
session. Simply providing a "text dump" of content to an assistive technology,
for example, would make it extremely difficult for assistive technologies to
provide timely access (as the assistive technology would have to recalculate
much more information rather than having information about incremental
changes).
Who benefits
- Users with a disability who rely on assistive technologies for input and
output.
Related techniques
- See the appendix that explains how to load assistive
technologies for DOM access.
Doing more
- Alert the user when information may be lost due to communication
delays.
7.1 Respect focus and selection conventions. (P1)
Checkpoint 7.1
- Follow operating environment
conventions that benefit accessibility when
implementing the selection, content focus, and user interface focus.
Note: See checkpoints 9.1 and 9.2
for more information about content focus and user interface focus.
Who benefits
- Many users with many types of disabilities.
Related techniques
- See techniques for checkpoint
7.3.
References
- Refer to
Selection and Partial Selection of DOM Level 2 ([DOM2RANGE], section
2.2.2).
- For information about focus in the Motif environment (under X Windows),
refer to the OSF/Motif Style Guide [MOTIF].
7.2 Respect input configuration conventions. (P1)
Checkpoint 7.2
- Ensure that default input configurations of the user
agent do not interfere with operating environment
accessibility conventions (e.g., for keyboard accessibility).
Note: See checkpoint 11.5 for information about the user agent's
default input configuration.
Who benefits
- Many users with many types of disabilities.
Example techniques
- The default configuration should not include
"Alt-F4",
"Control-Alt-Delete", or other combinations
that have reserved meanings in a given operating environment.
- Clearly document any default configurations that depart from operating
environment conventions.
Related techniques
- Some reserved keyboard bindings are listed in the appendix on accessibility features of some operating
systems.
7.3 Respect operating environment
conventions. (P2)
Checkpoint 7.3
-
Follow operating
environment conventions that benefit accessibility. In particular, follow
conventions that benefit accessibility for
user interface design, keyboard configuration, product installation, and documentation.
- For the purposes of this checkpoint, an operating environment convention
that benefits accessibility is either
- one identified as such in operating environment design or accessibility
guidelines, or
- one that allows the author to satisfy any requirement of the "Web Content
Accessibility Guidelines 1.0" [WCAG10] or of the current
document.
- This checkpoint excludes the requirements of checkpoints 7.1 and 7.4.
- Conformance detail: For user
agent features.
Notes and rationale
- Much of the rationale behind the content requirements of User Agent
Accessibility Guidelines 1.0 also makes sense for the user agent user interface
(e.g., allow the user to turn off any blinking or moving user interface
components).
Who benefits
- Many users with many types of disabilities.
Example techniques
- Follow operating environment conventions for loading assistive
technologies. See the appendix on loading assistive
technologies for DOM access for information about how an assistive
technology developer can load its software into a Java Virtual Machine.
- Inherit operating
environment settings related to accessibility (e.g., for fonts, colors, natural language preferences, input
configurations, etc.).
- Ensure that any online services (e.g., automated update facilities,
download-and-install functionalities, and sniff-and-fill forms) observe
relevant operating environment conventions concerning device independence and
accessibility (as well as the Web Content Accessibility Guidelines 1.0 [WCAG10]).
- Evaluate the conventional user interface
controls on the target platform against any built-in operating environment
accessibility functions (see the appendix on
accessibility features of some operating systems). Ensure that the user
agent operates properly with all these functions. Here is a sample of features
to consider:
- Microsoft Windows offers an accessibility function called "High Contrast".
Standard window classes and controls automatically support this setting.
However, applications created with custom classes or controls work with the
"GetSysColor" API to ensure compatibility with High Contrast.
- Apple Macintosh offers an accessibility function called "Sticky Keys".
Sticky Keys operate with keys the operating environment recognizes as modifier
keys, and therefore a custom control should not attempt to define a new
modifier key.
- Maintain consistency in the user interface between versions of the
software. Consistency is less important than improved general accessibility and
usability when implementing new features. However, developers should make
changes conservatively to the layout of user interface controls, the
behavior of existing functionalities, and the default keyboard
configuration.
Related techniques
- See techniques for checkpoint
6.5 and checkpoint
7.2.
References
- Follow accessibility guidelines for specific operating environments:
- "GNOME Accessibility Project" [GNOME-ACCESS]
- "How to Develop Accessible Linux Applications"
[ACCESSIBILITY-DEV-HOWTO]
- "Macintosh Human Interface Guidelines" [APPLE-HI]
- "IBM Guidelines for Writing Accessible Applications Using 100% Pure Java"
[JAVA-ACCESS].
- "An Inter-client Exchange (ICE) Rendezvous Mechanism for
X Window System Clients" [ICE-RAP].
- "Information for Developers About Microsoft Active Accessibility" [MSAA].
- "The Inter-Client communication conventions manual" [ICCCM].
- "Lotus Notes accessibility guidelines" [NOTES-ACCESS].
- "Java accessibility guidelines and checklist"
[JAVA-CHECKLIST].
- "The Java Tutorial. Trail: Creating a GUI with JFC/Swing"
[JAVA-TUT].
- "The Microsoft Windows Guidelines for Accessible Software Design"
[MS-SOFTWARE].
- Follow general guidelines for producing accessible software:
- "Accessibility for applications designers" [MS-ENABLE].
- "Application Software Design Guidelines" [TRACE-REF]. Refer also to "EZ
ACCESS(tm) for electronic devices V 2.0 implementation guide" [TRACE-EZ]
from the Trace Research and Development Center.
- Articles and papers from Sun Microsystems about accessibility
[SUN-DESIGN].
- "EITAAC Desktop Software standards" [EITAAC].
- "Requirements for Accessible Software Design" [ED-DEPT].
- "Software Accessibility" [IBM-ACCESS].
- Towards Accessible Human-Computer Interaction" [SUN-HCI].
- "What is Accessible Software" [WHAT-IS].
- Accessibility guidelines for Unix and X Window applications
[XGUIDELINES].
7.4 Provide input configuration indications. (P2)
Checkpoint 7.4
- Follow operating environment
conventions to indicate the input configuration.
Note: For example, in some operating environments, when a
functionality may be triggered through a menu and through the keyboard, the
developer may design the menu entry so that the character of the activating key
is also shown. See
checkpoint 11.5 for information about the user agent's default input
configuration.
Who benefits
- Many users with many types of disabilities.
Example techniques
- Use operating
environment conventions to indicate the current configuration (e.g., in
menus, indicate what key strokes will activate the functionality, underline
single keys that will work in conjunction with a key such as Alt,
etc.) These are conventions used by the Sun Java Foundations Classes [JAVA-TUT]
and Microsoft Foundations Classes for Windows.
- Ensure that information about changes to the input configuration is
available in a device-independent manner (e.g., through visual and audio cues,
and through text).
- If the current configuration changes locally (e.g., a search prompt opens,
changing the keyboard bindings for the duration of the prompt), alert the
user.
- Named configurations are easier to remember. This is especially important
for people with certain types of cognitive disabilities. For example, if the
invocation of a search prompt changes the input configuration, the user may
remember more easily which key strokes are meaningful in search mode if alerted
that there is a "Search Mode". Context-sensitive help (if available) should
reflect the change in mode, and a list of keybindings for the current mode
should be readily available to the user.
Related techniques
- See input configuration
techniques.
8.1 Implement accessibility features.
(P1)
Checkpoint 8.1
-
Implement the accessibility features of specifications (markup languages,
style sheet languages, metadata languages, graphics formats, etc.).
- This checkpoint applies to both W3C-developed and non-W3C
specifications.
- For the purposes of this checkpoint, an accessibility feature of a
specification is either:
- one identified as such in the specification, or
- one that allows the author to satisfy any requirement of the "Web Content
Accessibility Guidelines 1.0" [WCAG10].
- The user agent is not required to satisfy this checkpoint for all
implemented specifications; see the section on
conformance profiles for more information.
- Conformance detail: For all
content.
Who benefits
- Many users with many types of disabilities.
Example techniques
- Make obvious to users features that are known to benefit accessibility.
Make them easy to find in the user interface and in documentation.
- Some specifications include optional features (not required for conformance
to the specification). If an optional feature is likely to cause accessibility
problems, developers should either ensure that the user can turn off the
feature or they not implement the feature.
- Refer to the following list of accessibility features of HTML 4 [HTML4] (in
addition to those described in techniques for checkpoint 2.1):
References
- Refer to the "Accessibility Features of CSS"
[CSS-ACCESS]. Note that CSS 2 includes properties for configuring
synthesized speech styles.
- Refer to the "Accessibility Features of SMIL"
[SMIL-ACCESS].
- Refer to the "Accessibility Features of SVG"
[SVG-ACCESS].
- For information about the Sun Microsystems Java Accessibility API in Java
JDK, refer to
[JAVAAPI].
- For information about captioning for the Synchronized Accessible Multimedia
Interchange (SAMI), refer to [SAMI].
- Use and conform to
either
- W3C Recommendations when they are available and appropriate for a task,
or
- non-W3C specifications that enable the creation of content that conforms at
level A or better to the Web Content Accessibility Guidelines 1.0 [WCAG10].
- When a requirement of another specification contradicts a requirement of
the current document, the user agent may disregard the requirement of the other
specification and still satisfy this checkpoint.
- A specification is considered available if it is published (e.g., as a W3C
Recommendation) in time for integration into a user agent's development
cycle.
- The user agent is not required to satisfy this checkpoint for all
implemented specifications; see the section on
conformance profiles for more information.
- Conformance detail: For all
content.
Note: For instance, for markup, the user agent may conform to HTML 4 [HTML4], XHTML 1.0
[XHTML10], and/or XML 1.0 [XML]. For style
sheets, the user agent may conform to CSS ([CSS1], [CSS2]). For
mathematics, the user agent may conform to MathML 2.0 [MATHML20].
For synchronized multimedia, the user agent may conform to
SMIL 1.0
[SMIL].
Notes and rationale
- The right to disregard only applies when the requirement of another
specification contradicts the requirements of the current document; no
exemption is granted if the other specification is consistent with or silent
about a requirement made by the current document.
- Conformance to W3C Recommendations is not a priority 1 requirement because
user agents can (and should!) provide access for non-W3C specifications as
well.
- The requirement of this checkpoint is to conform to at least one
W3C Recommendation that is available and appropriate for a particular task, or
at least one non-W3C specification that allows the creation of content that
conforms to WCAG 1.0 [WCAG10]. For example, user agents
would satisfy this checkpoint by conforming to the Portable Network Graphics
1.0 specification
[PNG] for raster images. In addition, user agents may implement
other image formats such as JPEG, GIF, etc. Each specification defines what
conformance means for that specification.
Who benefits
- Many users with many types of disabilities.
Example techniques
- If more than one version or level of a specification is appropriate for a
particular task, user agents are encouraged to conform to the latest version.
However, developers should consider implementing the version that best supports
accessibility, even if this is not the latest version.
- For reasons of backward compatibility, user agents should generally
continue to implement deprecated features of specifications. Information about
deprecated language features is generally part of the language's
specification.
References
- The list of current W3C Recommendations and
other technical documents is available at
http://www.w3.org/TR/
.
- W3C make available validation services to promote the proper usage and
implementation of specifications. Refer to the:
- Information about PDF and accessibility is made available by Adobe [ADOBE].
- Provide at least one content focus for each viewport (including frames) where enabled elements are part of the rendered content.
- Allow the user to make the content focus
of each viewport the current focus.
- When a viewport includes no enabled elements (either because the format
does not provide for this, or a given piece of content has no enabled
elements), the content focus requirements of the following checkpoints do not
apply: 1.2, 5.1, 5.4, 6.6, 7.1, 9.3, 9.4, 9.5, 9.6, 9.7, 10.2, and 11.5.
Note: For example, when two frames of a frameset contain
enabled elements, allow the user to make the
content focus of either frame the current focus. Note that viewports
"owned" by plug-ins that are part of a conformance claim
are also covered by this checkpoint. See checkpoint 7.1 for
information about implementing content focus according to operating environment
conventions.
Who benefits
- Users who rely on the content focus for
interaction (e.g., for interaction with enabled elements through the keyboard,
or for assistive technologies that consider the current focus a point of regard). This includes some
users with blindness, low vision, or a physical disability.
9.2 Provide user interface focus. (P1) Checkpoint
9.2
-
Provide a user interface focus.
Note: See checkpoint 7.1 for information about implementing user
interface focus according to operating environment
conventions.
Who benefits
- Users who rely on the user interface
focus for interaction (e.g., for interaction with user interface controls
through the keyboard, or for assistive technologies that consider the current
focus a point of regard). This includes some
users with blindness, low vision, or a physical disability.
Example techniques
- Some operating
environments provide a means to move the
user interface focus among all open windows. It may be possible to satisfy
this checkpoint using the functionality provided by the operating
environment.
-
Allow the user to move the content focus to any enabled element in the viewport.
-
Allow configuration so that the content focus of
a viewport only changes on explicit user
request.
- If
the author has not specified a navigation order, allow at least forward sequential navigation, in
document order, to each element in the set established by provision one of this
checkpoint.
- To satisfy provision one of this checkpoint, configuration is preferred,
but is not required if the content focus only ever changes on explicit user request.
Note: In addition to forward sequential navigation, the
user agent should also allow reverse sequential navigation. See checkpoint 9.9 for information
about structured navigation. See checkpoints 5.1 and 6.6 for more information
about focus changes.
Who benefits
- Users who rely on the focus for interaction (e.g., for interaction with
enabled elements through the keyboard, or for assistive technologies that
consider the focus a point of regard). This includes some users with blindness,
low vision, or a physical disability.
- Allow the user to move the content focus to each enabled element by
repeatedly pressing a single key. Many user agents enable sequential navigation through
repeated keystrokes – for example, using the Tab key for
forward navigation and Shift-Tab for reverse navigation. Because the
Tab key is typically on one side of the keyboard while arrow keys
are located on the other, users should be allowed to configure the user agent
so that sequential navigation is possible with keys that are physically closer
to the arrow keys. See also
checkpoint 11.3 for information about overriding bindings in the default
input configuration.
- Maintain a logical element navigation order. For instance, users may use
the keyboard to navigate among elements or element groups using the arrow keys
within a group of elements. One example of a group of elements is a set of
radio buttons. Users should be able to navigate to the group of buttons, then
be able to select each button in the group. Similarly, allow users to navigate
from table to table, but also among the cells within a given table (up, down,
left, right, etc.).
- Respect author-specified information about navigation order (e.g., the
"tabindex" attribute in HTML 4 [HTML4], section
17.11.1). Allow users to override the author-specified navigation order (e.g.,
by offering an alphabetized view of links or other orderings).
- The default sequential navigation order should respect the conventions of
the natural language of the document.
Thus, for most left-to-right languages, the usual navigation order is
top-to-bottom and left-to-right. For right-to-left languages, the order would
be top-to-bottom and right-to-left.
- Implement the
':hover', ':active', and ':focus' pseudo-classes of CSS 2 ([CSS2], section
5.11.3). This allows users to modify content focus presentation with user style
sheets. Use them in conjunction with the
CSS 2 ':before' pseudo-elements ([CSS2], section 5.12.3) to clearly
indicate that something is a link (e.g., 'A:before { content : "LINK:"
}').
- In Java, a component is part of the sequential navigation order
when added to a panel and its
isFocusTraversable
method returns
true. A component can be removed from the navigation order by extending the
component, overloading this method, and returning false.
-
Doing more
- Provide other sequential
navigation mechanisms for particular element types or semantic units, e.g.,
"Find the next table" or "Find the previous form." For more information about
sequential navigation of form controls and
form submission, see techniques for checkpoint 5.5.
- For graphical user interfaces (or for any user agent offering a
two-dimensional display), navigation based not on document order but on layout
may also benefit the user. For example, allow the user to navigate up, down,
left, and right to the nearest rendered enabled link. This type of navigation
may be particularly useful when it is clear from the layout where the next
navigation step will take the user (e.g., grid layouts where it is clear what
the next link to the left or below will be).
- Excessive use of sequential
navigation can reduce the usability of software for both disabled and
non-disabled users. Some useful types of direct navigation include: navigation
based on position (e.g., all links are numbered by the user agent), navigation
based on element content (e.g., the first letter of text content),
direct navigation to a table cell by its row/column position, and searching
(e.g., based on form element text, associated labels, or form element
names).
9.4 Restore viewport state history.
(P1)
Checkpoint 9.4
- For user agents that implement a
viewport history mechanism, for each state in a
viewport's browsing history, maintain information about the point of regard, content focus, and selection.
- When the user returns to any state in
the viewport history (e.g., via the "back button"), restore the saved values
for the point of regard, content focus, and selection.
- The viewport history associates values for these three state variables (point of regard, content focus, and selection) with a particular document
object. If the user returns to a state in the history and the user agent
retrieves new content, the user agent is not required to restore the saved
values of the three state variables.
- Conformance
profile labels:
Selection.
Notes and rationale
- This checkpoint only refers to a per-viewport history mechanism, not a
history mechanism that is common to all viewports (e.g., of visited Web
resources).
Who benefits
- Users who may have difficulty re-orienting themselves during a browsing
session. This includes some users with a memory or cognitive disability, some
users with a physical disability, and some users with
serial access to content or who navigate sequentially, for whom
repositioning will be time-consuming.
Example techniques
- For each state in the history, keep track of the last time the content was
modified. When returning to that state in the history, restore the three state
variables of the content being rendered as long as the content has not been
retrieved more recently than that date.
- If the user agent allows the user to browse multimedia or audio-only presentations,
when the user leaves one presentation for another, pause the presentation. When
the user returns to a previous presentation, allow the user to resume the
presentation where it was paused (i.e., return the point of regard to the same place in
space and time). Note: This may be done for a presentation that is available
"completely" but not for a "live" stream or any part of a presentation that
continues to run in the background.
- Allow the user to configure whether leaving a viewport pauses a multimedia
presentation.
- If the user activates a broken link, leave the viewport where it is and
alert the user (e.g., in the status bar and with a
graphical or audio alert). Moving the viewport suggests that a link is not
broken, which may disorient the user.
- In JavaScript, the following may be used to change the Web resource in the
viewport, and navigate the history:
myWindow.home();
myWindow.forward();
myWindow.back();
myWindow.navigate("http://example.com/");
myWindow.history.back();
myWindow.history.forward();
myWindow.history.go( -2 );
location.href = "http://example.com/"
location.reload();
location.replace("http://example.com/");
Doing more
- Restore the point of regard, content focus, and selection after the user
reloads the same content.
References
- Refer to the HTTP/1.1 specification for information about history
mechanisms ([RFC2616], section 13.13).
- Allow
configuration so that moving the
content focus to or from an enabled element does not
automatically activate any explicitly associated event handlers of any event type.
Note: For instance, in this configuration for an HTML
document, do not activate any handlers for the 'onfocus
',
'onblur
', or 'onchange
' attributes. In this
configuration, user agents should still apply any stylistic changes (e.g., highlighting) that may occur when there is
a change in content focus.
Notes and rationale
- Event handlers associated with setting (or removing focus) may cause
disorienting changes to content. The purpose of this checkpoint is to reduce
unexpected changes while navigating with the focus.
Who benefits
- Users with blindness or some users with a physical disability, and anyone
without a pointing device.
Example techniques
- Allow the following configurations:
- On invocation of the input binding, move focus to the associated enabled
element, but do not activate it.
- On invocation of the input binding, move focus to the associated enabled
element and prompt the user with information that will allow the user to decide
whether to activate the element (e.g., link title or text). Allow the user to
suppress future prompts for this particular input binding.
- On invocation of the input binding, move focus to the associated enabled
element and activate it.
-
For the element with content focus, make
available the list of input device event types for which there are event handlers explicitly associated
with the element.
Note: For example, allow the user to query the element with
content focus for the list of input device event types, or add them directly to
the sequential navigation order
described in checkpoint 9.3. See
checkpoint 1.2
for information about activation of event handlers associated with the element
with focus.
Who benefits
- Users with blindness or some users with a physical disability, and anyone
without a pointing device.
Example techniques
- For HTML content, the left mouse button is generally the only mouse button
that is used to activate event handlers associated with mouse clicks.
- Authors may specify redundant event handlers (e.g., the same handler for
both
onmouseover
and onfocus
events). When the user
agent recognizes the same handler for two event types, present only one of them
to avoid confusion.
- When using the "Document Object Model (DOM) Level 3 Events Specification"
[DOM3EVENTS], find the list of event types for which there are event
handlers explicitly associated with an element as described in
section 1.3.1, using the methods
EventTarget.canTrigger/EventTarget.isRegisteredHere
and
EventTarget.canTrigger/Event.isRegisteredHere
. The first method provides
information about the target node only, the second about whether there are
handlers on any node in the path between the target node and the root
node.
References
- See checkpoint
1.2 for information about input device event handlers in HTML 4 [HTML4] and the
Document Object Model (DOM) Level 2 Events Specification
[DOM2EVENTS].
9.7 Move content focus in reverse. (P2)
Checkpoint 9.7
- Extend the functionality required in
provision three of checkpoint 9.3
by allowing the same sequential
navigation in reverse document order.
- As part of satisfying provision one of this
checkpoint, the user agent must not include disabled elements in the navigation
order.
Who benefits
- Users who rely on the focus for interaction (e.g., for interaction with
enabled elements through the keyboard, or for assistive technologies that
consider the focus a point of regard). This includes some users with blindness,
low vision, or a physical disability.
Related techniques
- Apply the techniques of
checkpoint 9.3 to enabled elements only.
Doing more
- Allow configuration so that disabled elements are included in
the navigation order. These elements cannot be activated, but their presence
may lend continuity to navigation.
-
Allow the user to search within rendered text content for a sequence
of characters from the document character
set.
-
Allow the user to start a forward search (in document order) from any selected
or focused location in content.
-
When there is a match, do both of the following:
- move the viewport so that the matched text content is within it,
and
- allow the user to search for the next instance of the text from the
location of the match.
-
Alert the user when there is no match or after the last match in content (i.e.,
prior to starting the search over from the beginning of content).
-
Provide a case-insensitive search option for text in scripts
(i.e., writing systems) where case is significant.
Note: If the user has not indicated a start position for
the search, the search should start from the beginning of content. Per checkpoint 7.3, use operating environment
conventions for indicating the result of a search (e.g., selection or
content focus).
Notes and rationale
- This checkpoint involves searching through rendered content only.
Thus, the user agent should not search through unrendered conditional content. It may be
confusing to allow users to search for text content that is not
rendered (and thus that they have not viewed). Since checkpoint 2.3 requires
that the user have access to conditional content, the user can search through
that content once rendered.
Who benefits
- Some users with serial access to content
or who navigate sequentially, some
users with a cognitive disability (who may have difficulty locating information
among other information), and some users with a physical disability (for whom
navigation may be a significant effort).
Example techniques
- Use the selection or focus to indicate found text. This will provide
assistive technologies with access to the text.
- Allow users to search all views (e.g., including views of the text
source).
- For extremely small viewports or extremely long matches, the entire matched
text content may not fit within the viewport. In this case, developers may move
the viewport to encompass the initial part of the matched content.
- The search string input method should follow operating environment
conventions (e.g., for international character input).
- When the point of regard depends on time (e.g., for audio viewports), the
user needs to be able to search through content that will be available through
that viewport. This is analogous to content rendered graphically that is
reachable by scrolling.
- For multimedia presentations, allow users to search and examine
time-dependent media elements and links in a time-independent manner. For
example, present a static list of time-dependent links.
- Allow users to search the element content of form elements (where
applicable) and any label text.
- When searching a document, the user agent should not search text whose
properties prevent it from being visible (such as text that has
visibility="hidden"
), or equivalent text for elements with such
properties (such as "alt
" text for an image that has
visibility="hidden"
).
Doing more
- Allow reverse search in addition to forward search.
- Allow the user to start a search from the beginning of the document rather
than from the current selection or focus.
- Provide distinct alerts for when there are no matches and when there are no
more matches.
- Allow the user to easily start a search from the beginning of the content
currently rendered in the viewport.
- Provide the option of searching through conditional content that is
associated with rendered content, and render the found conditional content
(e.g., by showing its relation to the rendered content).
- For frames, allow users to search for content in all frames, without having
to be in a particular frame.
- If the number of matches is known, provide this information to orient the
user.
References
- For information about when case is significant in a script,
refer to Section 4.1 of Unicode [UNICODE].
9.9 Allow structured navigation. (P2)
Checkpoint 9.9
-
Allow the user to navigate efficiently to and among important structural
elements in rendered content.
-
As part of satisfying provision one of this checkpoint, allow forward and
backward sequential
navigation.
Note: This specification intentionally does not identify
which "important elements" must be navigable as this will vary by
specification. What constitutes "efficient navigation" may depend on a number
of factors as well, including the "shape" of content (e.g., sequential
navigation of long lists is not efficient) and desired granularity (e.g., among
tables, then among the cells of a given table).
Notes and rationale
- User agents should construct the navigation view with the goal of breaking
content into sensible pieces according to the author's design. In most cases,
user agents should not break down content into individual elements for
navigation; element-by-element navigation of the document object does not meet
the goal of facilitating navigation to important pieces of content. (The
navigation view may also serve as an expanding/contracting outline view; see
the outline view requirement of checkpoint 10.4.) Instead, user agents are expected to
construct the navigation view based on markup.
Who benefits
- Users with serial access to content or who navigate sequentially.
Example techniques
- In HTML 4
[HTML4], important elements include:
A
,
ADDRESS
, APPLET
, BUTTON
,
FIELDSET
, DD
, DIV
, DL
,
DT
, FORM
, FRAME
, H1-H6
,
IFRAME
, IMG
, INPUT
, LI
,
LINK
(if rendered), MAP
, OBJECT
,
OL
, OPTGROUP
, OPTION
, P
,
TABLE
, TEXTAREA
, and UL
. HTML also allows
authors to specify keyboard configurations ("accesskey", "tabindex"), which can
serve as hints about what the author considers important.
- Allow navigation based on commonly understood document models, even if they
do not adhere strictly to a document type definition (DTD) or schema. For instance, in
HTML, although headings (H1-H6) are not containers, they may be treated as such
for the purpose of navigation. Note that they should be properly nested.
- Use the DOM ([DOM2CORE]) as the basis of
structured navigation (e.g., a postorder traversal). However, for well-known
markup languages such as HTML, structured navigation should take advantage of
the structure of the source tree and what is rendered.
- Follow operating
environment conventions for indicating navigation progress (e.g., selection or
content focus).
- Allow the user to limit navigation to the cells of a table (notably left
and right within a row and up and down within a column). Navigation techniques
include keyboard navigation from cell to cell (e.g., using the arrow keys) and
page up/down scrolling. See the section on table
navigation.
- Alert the user when navigation has led to the beginning or end of a
structure (e.g., end of a list, end of a form, table row or column end, etc.).
See checkpoint 1.3 for
information about text messages to the user.
- For those languages with known (e.g., by specification, schema, metadata,
etc.) conventions for identifying important components, user agents should
construct the navigation tree from those components, allowing users to navigate
up and down the document tree, and forward and backward among siblings. As the
same time, allow users to shrink and expand portions of the document tree. For
instance, if a subtree consists of a long series of links, this will pose
problems for users with serial access to content
or who navigate sequentially. At any
level in the document tree (for forward and backward navigation of siblings),
limit the number of siblings to between five and ten. Break longer lists down
into structured pieces so that users can access content efficiently, decide
whether they want to explore it in detail, or skip it and move on.
- Tables and forms illustrate the utility of a recursive navigation
mechanism. The user should be able to navigate to tables, then change "scope"
and navigate within the cells of that table. Nested tables (a table within the
cell of another table) fit nicely within this scheme. The same ideas apply to
forms: users should be able to navigate to a form, then among the controls within that
form.
- Navigation and orientation go together. The user agent should allow the
user to navigate to a location in content, explore the context, navigate again,
etc. In particular, user agents should allow users to:
- Navigate to a piece of content that the author has identified as important
according to the markup language specification and conventional usage. In HTML,
for example, this includes headings, forms, tables, navigation mechanisms, and
lists.
- Navigate past that piece of content (i.e., avoid the details of that
component).
- Navigate into that piece of content (i.e., chose to view the details of
that component).
- Change the navigation view as they go, expanding and contracting portions
of content that they wish to examine or ignore. This will speed up navigation
and facilitate orientation at the same time.
- Provide context-sensitive navigation. For instance, when the user navigates
to a list or table, provide locally useful navigation mechanisms (e.g., within
a table, cell-by-cell navigation) using similar input commands.
- Allow users to skip author-specified navigation mechanisms such as
navigation bars. For instance, navigation bars at the top of each page at a Web
site may force users with screen readers or some physical disabilities to wade
through many links before reaching the important information on the page. User
agents may facilitate browsing for these users by allowing them to skip recognized navigation bars (e.g., through a
configuration option). Some techniques for this include:
- Providing a functionality to jump to the first non-link content.
- If the number of elements of a particular type is known, provide this
information to orient the user.
- In HTML, the MAP element may be used to mark up a navigation bar (even when
there is no associated image). Thus, users might ask that MAP elements not be
rendered in order to hide links inside the MAP element. User agents might allow
users to hide MAP elements selectively. For example, hide any MAP element with
a "
title
" attribute specified. Note: Starting in
HTML 4, the MAP element allows block content, not just AREA
elements.
- Allow depth-first and breadth-first navigation through the document
object.
Doing more
- Allow the user to navigate characters, words, sentences, paragraphs,
screenfuls, etc. according to conventions of the natural language. This benefits
users of synthesized speech-based user agents and has been implemented by
several screen readers, including Winvision [WINVISION], Window-Eyes
[WINDOWEYES], and JAWS for Windows [JFW].
Related techniques
- See checkpoint 4.5
for information about navigating synchronized multimedia presentations.
References
- The following is a summary of ideas provided by the National Information
Standards Organization with respect to Digital Talking Books
[TALKINGBOOKS]:
- A talking book's "Navigation Control Center" (NCC) resembles a traditional
table of contents, but it is more. It contains links to all headings at all
levels in the book, links to all pages, and links to any items that the reader
has chosen not to have read. For example, the reader may have turned off the
automatic reading of footnotes. To allow the user to retrieve that information
efficiently, the reference to the footnote is placed in the NCC and the reader
can go to the reference, understand the context for the footnote, and then read
the footnote.
- Once the reader is at a desired location and wishes to begin reading, the
navigation process changes. Of course, the reader may elect to read serially,
but often some navigation is required (e.g., frequently people navigate forward
or backward one word or character at a time). Moving from one sentence or
paragraph at a time is also needed. This type of local navigation is different
from the global navigation used to get to the location of what you want to
read. It is frequently desirable to move from one block element to the next.
For example, moving from a paragraph to the next block element which may be a
list, blockquote, or sidebar is the normally expected mechanism for local
navigation.
- Allow
configuration of the set of important elements and attributes identified
for checkpoints 9.9 and 10.4.
- As part of satisfying provision one of
this checkpoint, allow the user to include and exclude element types in the
set.
Note: For example, allow the user to navigate only
paragraphs, or only headings and paragraphs, or to suppress and restore
navigation bars, to navigate within and among tables and table cells, etc.
Who benefits
- Users with serial access to content or who navigate sequentially.
Example techniques
- Allow the user to navigate HTML elements that share the
same "class" attribute.
- The CSS
'display' and
'visibility' properties ([CSS2], sections 9.2.5 and 11.2,
respectively), allow the user to override the default settings in user style sheets.
Doing more
- Allow the user to navigate according to similar styles (which may be an
approximation for similar element types).
10.1 Associate table cells and headers.
(P1)
Checkpoint 10.1
-
For graphical user agents that render tables, for each table cell, allow
the user to view associated header information.
- The user agent may satisfy this checkpoint by allowing the user to query
each table cell for associated header information.
- The user agent may satisfy this checkpoint by rendering the table cell and
associated header information so they are both visible in the same
viewport.
- This checkpoint refers only to cell/header relationships that the user
agent can
recognize.
Notes and rationale
- A cell may be associated with more than one header.
Who benefits
- Users for whom two-dimensional relationships may be difficult to process
(e.g., users with serial access to content
or who navigate sequentially, or some
users with a cognitive disability). Renderings that provide easy access to cell
header information will also help some users with low vision or a physical
disability, for whom it may be time-consuming to scroll in order to locate
relevant headers.
Example techniques
- When rendering the table cell and associated header information so they are
both visible in the same viewport, use a technique frequently employed by
spreadsheet applications: the user agent fixes the position of headers in the
viewport and allows the user to scroll through associated data cells. Through
horizontal and vertical alignment, the data cells and header cells are visually
associated.
- The headers of a nested table may provide important context for the cells
of the same row(s) or column(s) containing the nested table.
- The
THEAD, TBODY, and TFOOT elements of HTML 4 ([HTML4], section 11.2.3) allow users
to specify portions of a large table that should remain available (e.g., when
scrolling). When a table is constructed with a
TBODY
element, the
'overflow' property of CSS 2 ([CSS2], section 11.1.1) may be used
to create a scrollable area.
tbody { height: 10em; overflow: auto }
- In HTML, beyond the
TR
, TH
, and TD
elements, the table attributes "summary", "abbr", "headers", "scope", and
"axis" also provide information about relationships among cells and headers.
For more information, see the section on table
techniques.
Doing more
- Make available (e.g., through a context menu)
information summarizing table structure, including any table head and foot
rows, and possible row grouping into multiple table bodies, column groups,
header cells and how they relate to data cells, the grouping and spanning of
rows and columns that apply to qualify any cell value, cell position
information, table dimensions, etc.
- When providing serial access to a
table, allow the user to specify how cell header information should be rendered
before cell data information. Some possibilities are illustrated by the
CSS2 'speak-header' property ([CSS2], section 17.7.1).
-
10.2 Highlight selection, content focus, enabled elements, visited
links. (P1)
Checkpoint 10.2
- Allow global configuration to highlight the following four classes of
information in each viewport: the selection, content focus, enabled elements, and recently
visited links.
- For graphical user interfaces, as part
of satisfying provision one of this checkpoint, allow at least one
configuration where the highlight mechanisms for the four classes of
information:
- differ from each other, and
- do not rely on rendered text foreground
and background colors alone.
- For graphical user interfaces, as part
of satisfying provision one of this checkpoint, if a highlight mechanism
involves text size, font family,
rendered text foreground and background colors, or text decorations, offer
at least the following range of values:
- for text size, the range required by provision three of checkpoint 4.1.
- for font family, the range required by provision three of checkpoint 4.2.
- for text foreground and background colors and decorations, the range
offered by the conventional utility available in the operating environment for
users to choose rendered text colors or decorations (e.g., the standard font
and color dialog box resources supported by the operating system). If no such
utility is available, the range supported by the conventional APIs of the
operating environment for specifying text colors or drawing text.
- Highlight enabled elements according to the
granularity specified in the format. For example, an HTML user agent rendering
a PNG image as part of a client-side image map is only required to highlight
the image as a whole, not each enabled region. An SVG user agent rendering an
SVG image with embedded graphical links is required to highlight each (enabled) link that may be rendered
independently according to the SVG specification.
Note: Examples of highlight mechanisms for selection and
content focus include foreground and background color variations, underlining,
distinctive synthesized speech prosody, border styling, etc. Because the
selection and focus change frequently, user agents should not highlight them
using mechanisms (e.g., font size variations) that cause content to reflow, as
this may disorient the user. Graphical highlight mechanisms that generally do
not rely on rendered text foreground and background color alone include
underlines or border styling. Per checkpoint 7.1, follow operating environment conventions
that benefit accessibility when implementing the selection and content focus.
For instance, if specified at the level of the operating environment, inherit
the user's preferences for selection styles.
Notes and rationale
- In many graphical user interfaces, all links on a page are highlighted so
that users know at a glance where to interact.
Who benefits
- Users with color deficiencies, low vision, or blindness, for whom color may
not be useful. Also, some devices may not render colors (e.g., speech
synthesizers, black and white screens). If highlighting is done through text
styles, some users with low vision may need to configure them.
Example techniques
- Inherit selection and focus
information from user's settings for the operating environment. Explain
in the user agent documentation where to find information in the operating
environment documentation about changing these settings.
- For content highlighting:
- Use CSS2
[CSS2] to add style to these different classes of elements. In
particular, consider the
'text-decoration' property ([CSS2], section 16.3.1), aural
cascading style sheets, font properties, and color properties.
- For enabled elements, implement CSS2
attribute selectors to match elements with associated scripts ([CSS2], section
5.8).
-
- For selection:
- For focus, implement the
':hover', ':active', and ':focus' pseudo-classes of CSS 2 ([CSS2], section
5.11.3). and
dynamic outlines and focus of CSS 2 ([CSS2], sections 5.11.3 and 18.4.1,
respectively).
Example.
The following rule will cause links with focus to appear with a blue
background and yellow text.
A:focus { background: blue; color: yellow }
The following rule will cause TEXTAREA
elements with focus to
appear with a particular focus outline:
TEXTAREA:focus { outline: thick black solid }
Doing more
- During configuration, warn the user of potential highlighting conflicts
(e.g., same highlight mechanism used for two classes of information, or
insufficient contrast likely).
- Test the user agent to ensure that individuals who have low vision and use
screen magnification software are able to follow highlighted item(s).
Related techniques
- For information about highlighting links, see the section on link techniques, the visited links example in the
section on generated content techniques, and
techniques for checkpoint
9.3.
- For Windows, see information about
ChooseFont
and
ChooseColor
in techniques for checkpoint 4.1, checkpoint 4.2, and checkpoint 4.3. ChooseFont
is also used to
choose some text decorations in Windows.
- Extend the functionality required by
provision two of
checkpoint 10.2 by allowing configuration through a
single setting.
Notes and rationale
- A single configuration should help the user avoid conflicts between
multiple highlight settings (e.g., same highlight mechanism used for two
classes of information, or insufficient contrast).
Who benefits
- Users with color deficiencies, low vision, or blindness. Any user who may
find it difficult to locate and configure multiple settings.
Example techniques
- Offer a number of predefined configurations tailored to users with low
vision (e.g., "Large text size") or color deficiencies (e.g., "High contrast"),
or both.
- Allow the user to use those predefined configurations as templates for
building specialized configurations (e.g., named configurations that may be
easily invoked).
- Make available to the user an "outline"
view of rendered content, composed of labels
for important structural elements (e.g., heading text, table titles, form
titles, and other labels that are part of the content).
- What constitutes a label is defined by each markup language specification.
For example, in HTML, a heading (
H1
-H6
) is a label
for the section that follows it, a CAPTION
is a label for a table,
the "title
" attribute is a label for its element, etc.
- The user agent is not required to generate a label for an important element
when no label is present in content. The user agent may generate a label when
one is not present.
- A label is not required to be text only.
Note: This outline view will provide the user with a
simplified view of content (e.g, a table of contents). For information about
what constitutes the set of important structural elements, see the Note
following checkpoint 9.9. By
making the outline view navigable, it is possible to satisfy this checkpoint
and checkpoint 9.9 together:
allow users to navigate among the important elements of the outline view, and
to navigate from a position in the outline view to the corresponding position
in a full view of content. See checkpoint 9.10 for additional configuration options.
Who benefits
- Users with a memory or cognitive disability, as well as users with serial access to content or who navigate sequentially. The
outline view is a type of summary view and should reduce orientation time. A
navigable outline view will add further benefits for these users.
Example techniques
- For instance, in HTML, labels include the following:
- The
CAPTION
element is a label for TABLE
- The "
title
" attribute is a label for many elements.
- The
H1
-H6
elements are labels for sections that
follow
- The
LABEL
element is a label for the form element
- The
LEGEND
element is a label for a set of form elements
- The
TH
element is a label for a row/column of table
cells.
- The
TITLE
element is a label for the document.
- Allow the user to expand or shrink portions of the outline view (configure
detail level) for faster access to important parts of content.
- Hide portions of content by using the CSS
'display' and
'visibility' properties ([CSS2], sections 9.2.5 and 11.2,
respectively).
- Provide a structured view of form controls (e.g., those grouped
by
LEGEND
or OPTGROUP
in HTML) along with their
labels.
-
Related techniques
- See structured navigation techniques for checkpoint 9.9.
Doing more
- For improperly structured documents, user agents may attempt to create an
outline based on the rendering of elements and heuristics about what elements
may indicate about document structure.
- To
help the user decide whether to traverse a link in content,
make available the following information about it:
- link element content,
- link title,
- whether the link is internal to the resource (e.g., the link is to a target
in the same Web page),
- whether the user has traversed the link recently, and
- information about the type, size, and natural language of linked Web
resources.
- The user agent is not required to compute or make available information
that requires retrieval of linked Web
resources.
Who benefits
- Users for whom following a link may lead to loss of context upon return,
including some users with blindness and low vision, some users with a cognitive
disability, and some users with a physical disability.
Example techniques
- Some markup languages allow authors to provide hints about the nature of
linked content (e.g., in HTML 4 [HTML4], the "hreflang" and "type"
attributes on the A element). Specifications should indicate when this type of
information is a hint from the author and when these hints may be overridden by
another mechanism (e.g., by HTTP headers in the case of HTML). User agent
developers should make the author's hints available to the user (prior to
retrieving a resource), but should provide definitive information once
available.
- Links may be simple (e.g., HTML links) or more complex, such as those
defined by the XML Linking Language (XLink) [XLINK].
- The scope of "recently followed link" depends on the user agent. The user
agent may allow the user to configure this parameter, and should allow the user
to reset all links as "not followed recently".
- User agents should cache information determined as the result of retrieving
a Web resource and should make it available to the user. Refer to HTTP/1.1
caching mechanisms described in RFC 2616 [RFC2616], section 13.
- For a link that has content focus, allow the
user to query the link for information (e.g., by activating a menu or key
stroke).
- Do not mark all local links (to anchors in the same page) as visited when
the page has been visited.
Related techniques
- See the section on link techniques.
Doing more
- Provide information about any input bindings associated with a link; see checkpoint 11.2 for
information about author-specified input bindings.
- Allow configuration to prompt the
user to confirm (or cancel) any payment that results from activation of a fee link. For the purpose of
this document, the term fee link refers to a link that when activated, debits
the user's electronic "wallet" (generally, a "micropayment"). The link's role
as a fee link is identified through markup (in a manner that the user agent can
recognize). This definition of fee link
excludes payment mechanisms (e.g., some form-based credit card transactions)
that cannot be recognized by the user agent as causing payments. Note: Previous
versions of UAAG 1.0 included requirements related to fee links.
- Additional fee link techniques:
- While configuration to prompt before payment is preferred, it is sufficient
(to meeting the goal of informed consent) to only ever allow activation of fee
links on explicit user request.
- Allow the user to configure the user agent to prompt for payments above a
certain amount (including any payment). Warn the user that even in this
configuration, the user agent may not be able to recognize some payment
mechanisms.
References
- User agents may use HTTP HEAD rather than GET for information about size,
language, etc. Refer to RFC 2616 [RFC2616], section 9.3
- For information about content size in HTTP/1.1, refer to RFC 2616 [RFC2616],
section 14.13. User agents are not expected to compute content size recursively
(i.e., by adding the sizes of resources referenced by URIs within another
resource).
- For information about content language in HTTP/1.1, refer to RFC 2616
[RFC2616], section 14.12.
- For information about content type in HTTP/1.1, refer to RFC 2616 [RFC2616],
section 14.17.
-
Highlight the viewport with the
current focus (including any frame that takes current focus).
- For graphical viewports, as part of
satisfying provision one of this checkpoint, provide at least one highlight
mechanism that does not rely on
rendered text foreground and background colors alone (e.g., use a thick
outline).
- If the techniques used to satisfy
provision one of this checkpoint involve
rendered text size, font family,
rendered text foreground and background colors, or text decorations, allow
global configuration and offer
same ranges of values required by provision three of checkpoint 10.2.
Note: See checkpoint 7.1 for information about implementing highlight
mechanisms according to operating environment
conventions.
Who benefits
- Users with color deficiencies or blindness, for whom color will not be
useful. Also, some devices may not render colors (e.g., speech synthesizers,
black and white screens).
Example techniques
- Offer a configuration whereby a window that is the viewport with the
current focus is brought to the foreground, or maximized automatically. For
example, maximize the parent window of the browser when launched, and maximize
each child window automatically when it receives focus.
Maximizing does not necessarily mean occupying the whole screen or parent
window; it means expanding the viewport in a manner that reduces the amount of
horizontal and vertical scrolling required of the user.
- If the viewport with the current focus is a frame or the user does not want
windows to pop to the foreground, use border colors, reverse videos, or other
graphical clues to indicate the viewport with the current focus.
- If the default highlight mechanism is inherited from the operating
environment, document how to change it, or explain where to find this
information in the documentation for the operating environment.
- For synthesized speech or braille output, use the frame or window title to
identify the viewport with the current focus.
- Use operating
environment conventions, for specifying selection and content focus (e.g.,
schemes in Windows).
- Implement the
':hover', ':active', and ':focus' pseudo-classes of CSS 2 ([CSS2], section
5.11.3). This allows users to modify content focus rendering with user style sheets.
-
Related techniques
- See the section on frame techniques.
- Indicate the
viewport's position relative to rendered content (e.g., the
proportion of an audio or video clip that has been played, the proportion of a
Web page that has been viewed, etc.).
- The user agent may calculate the relative position according to content
focus position, selection position, or viewport position, depending on how the
user has been browsing.
- The user agent may indicate the proportion of content viewed in a number of
ways, including as a percentage, as a relative size in bytes, etc. See checkpoint 1.3 for more information
about text versions of messages to the user, including messages about position
information.
- For two-dimensional spatial renderings,
relative position includes both vertical and horizontal positions.
- This checkpoint does not require the user agent to present information
about retrieval progress. However, for streaming content, viewport
position may be closely tied to retrieval progress.
Notes and rationale
- This checkpoint does not specify how to calculate the proportion in all
cases, and implementations may vary. For instance, suppose a user agent is to
render fifty audio clips one after the other. It may be costly to calculate the
proportion based on the total time required by all fifty clips (as this may
require the user agent to fetch all fifty in advance). Instead, the user agent
may represent the proportion as something like "2:43 remaining in the tenth
audio clip (of fifty)."
Who benefits
- Users with serial access to content or who navigate sequentially and some
users with a cognitive disability. This type of context information generally
benefits all users.
Example techniques
- The proportion should be indicated using a relative value where applicable
(e.g., 25%), otherwise as an absolute offset (e.g., 3k) from some recognized
landmark.
- Provide a scrollbar for the viewport. Some specifications address scrolling
requirements or suggestions, such as for
the
THEAD
and TBODY
elements of HTML 4 ([HTML4], section
11.2.3) and the
'overflow' property of CSS 2 ([CSS2], section 11.1.1).
- Indicate the size of the document, so that users may decide whether to
download for offline viewing. For example, the playing time of an audio file
could be stated in terms of hours, minutes, and seconds. The size of a
primarily text-based Web page might be stated in both kilobytes and screens,
where a screen of information is calculated based on the current dimensions of
the viewport.
- Indicate the number of screens of information, based on the current
dimensions of the viewport (e.g., "screen 4 of 10").
- Use a variable pitch audio signal to indicate the viewport's different
positions.
- Provide markers for specific percentages through the document.
- Provide markers for positions relative to some position – a user
selected point, the bottom, the
H1
, etc.
- Put a marker on the scrollbar, or a highlight at the bottom of the page
while scrolling (so you can see what was the bottom before you started
scrolling).
- For images that render gradually (coarsely to finely), it is not necessary
to show percentages for each rendering pass.
Doing more
- Allow users to configure what status information they want rendered. Useful
status information includes:
- Document proportions (numbers of lines, pages, width, etc.);
- Number of elements of a particular type (e.g., tables, forms, and
headings);
- Whether the viewport is at the beginning or end of the document;
- Size of document in bytes;
- The number of controls in a form and
controls in a form element group (e.g.,
FIELDSET
in HTML).
11.1 Current user input configuration.
(P1)
Checkpoint 11.1
- Provide information to the user about
current user preferences for input configurations.
- To satisfy this checkpoint, the user agent may make available binding
information in a centralized fashion (e.g., a list of bindings) or a
distributed fashion (e.g., by listing keyboard shortcuts in user interface
menus). See related documentation checkpoints 12.2, 12.3, and 12.5.
Who benefits
- Users with blindness (for whom the pointing device is not useful), users
with physical disabilities (who might mistakenly repeat a key stroke), users
who fatigue easily (for whom the composition of key sequences is a significant
effort), users who cannot remember key combinations, and any user who wants to
operate the user agent efficiently.
Related techniques
- See the input configuration
techniques.
11.2 Current author input configuration.
(P2)
Checkpoint 11.2
- Provide a centralized view of the
current author-specified input configuration.
- The user agent may satisfy this checkpoint by providing different views for
different input modalities (keyboard, pointing device, voice, etc.).
Note: For example, for HTML documents, provide a view of
keyboard bindings specified by the author through the "accesskey
"
attribute. The intent of this checkpoint is to centralize information about
author-specified bindings so that the user does not have to read an entire
document to look for available bindings.
Who benefits
- Users with blindness, some users with a physical disability, and some users
with a memory or cognitive disability.
Example techniques
- If the user agent offers a special view that lists author-specified
bindings, allow the user to navigate easily back and forth between the viewport
with the current focus and the list of bindings.
Related techniques
- See input configuration
techniques.
Doing more
- In addition to providing a centralized view of bindings, allow users to
find out about bindings in content. For example, highlight enabled elements
that have associated event handlers (e.g., by indicating bindings near the
element).
- Allow the user to override
any binding that is part of the user agent default input configuration.
- The user agent is not required to allow the user to override conventional
bindings for the operating
environment (e.g., for access to help).
- The override requirement only applies to bindings for the
same input modality (e.g., the user must be able to override a keyboard binding
with another keyboard binding).
- This checkpoint excludes the requirements of checkpoint 11.4.
- Conformance detail: For user
agent features.
Note: See checkpoint 11.5 for default input configuration requirements
and checkpoint 12.3
for information about their documentation.
Who benefits
- Users with blindness, some users with a physical disability, and some users
with a memory or cognitive disability.
Example techniques
- Allow the user to override bindings at the level of the operating
environment.
Related techniques
- See input configuration
techniques.
Doing more
- Allow users to choose from among prepackaged configurations, to override
portions of the chosen configuration, and to save it as a profile. Not only will the user save time
configuring the user agent, but this will reduce questions to technical support
personnel.
- Allow users to easily restore the default input configuration.
- Allow users to create macros and bind them to key strokes or other input
methods.
- Test the default keyboard configuration for usability. Ask users with
different disabilities and combinations of disabilities to test
configurations.
-
Allow the user to override any binding in the user agent
default keyboard configuration with a binding to either a key plus modifier
keys or to a single key.
- For
each functionality in the set required by checkpoint 11.5, allow the user to
configure a single-key binding. A single-key binding is one where a single
key press performs the task, with zero modifier keys.
- The user agent may satisfy the requirements of provision two of this
checkpoint with a "single-key mode" (i.e., a mode where the current bindings
are replaced by a set of single-key bindings).
- In this checkpoint, "key" refers to a physical key of the keyboard (rather
than, say, a character of the document character
set).
- The user agent is not required to allow the user to override
conventional bindings for the operating environment (e.g.,
for access to help).
- Provision two of this checkpoint does not require single physical key
bindings for character input, only for the activation of user agent
functionalities.
- If the number of physical keys on the keyboard is less than the number of
functionalities required by checkpoint 11.5, then provision two of this checkpoint does
not require the user agent to allow single-key bindings for all of the
functionalities. The user agent should give preference to those functionalities
listed in provision one of
checkpoint 11.5.
- This checkpoint is mutually exclusive of checkpoint 11.3 since it is specific to the keyboard and to
emphasize the importance of easy keyboard access.
- Conformance detail: For user
agent features.
Note: Because single-key access is so important to some
users with physical disabilities, user agents should ensure that: (1) most keys
of the physical keyboard may be configured for single-key bindings, and (2)
most functionalities of the user agent may be configured for single-key
bindings. For information about access to user agent functionality through a
keyboard API, see checkpoint
6.7.
Notes and rationale
- When using a physical keyboard, some users require single-key access,
others require that keys activated in combination be physically close together,
while others require that they be spaced physically far apart.
- In some modes of interaction (e.g., when the user is entering text), the
number of available single keys will be significantly reduced.
- A "single-key mode" allows user agents to "save" keys for other bindings by
default and still satisfy this checkpoint. However, even when a single-key mode
is offered, user agents should include as many required single-key bindings as
possible in the default keyboard configuration. The user should be able to
enter into a single-key mode by using a single-key.
Who benefits
- Users with a physical disability (for whom single-key access is
particularly important), and some users with a memory or cognitive disability
(who may require simple interaction).
Example techniques
- Offer a single-key mode where, once the user has entered into that mode
(e.g., by pressing a single key), most of the keys of the keyboard are
configurable for single-key operation of the user agent. Allow the user to exit
that mode by pressing a single key as well. For example, Opera [OPERA] includes a
mode in which users can access important user agent functionalities with single
strokes from the numeric keypad.
- Consider distance between keys and key alignment (e.g., "9/i/k", which
align almost vertically on many keyboards) in the default configuration. For
instance, if Enter is used to activate links, put other link
navigation commands near it (e.g., page up/down, arrow keys, etc., on many
keyboards). In configurations for users with reduced mobility, pair related
functionalities on the keyboard (e.g., left and right arrows for forward and
back navigation).
- Mouse Keys (available in some operating environments) allow
users to simulate the mouse through the keyboard. They provide a usable command
structure for individuals who require keyboard-only and single-access, without
interfering with the user interface for individuals who do not; see checkpoint 1.1 for more
information about keyboard access requirements.
Doing more
- Allow users to accomplish tasks through repeated key strokes (e.g., sequential navigation) since
this can mean less physical repositioning for all users. However, repeated key
strokes may not be efficient for some tasks. For instance, do not require the
user to position the pointing device by pressing the "down arrow" key
repeatedly.
- So that users do not mistakenly activate certain functionalities, make
certain combinations "more difficult" to invoke (e.g., users are not likely to
press Control-Alt-Delete accidentally).
- Ensure that the user agent default input configuration includes
bindings for the following functionalities required by other checkpoints in
this document:
- move content focus to the next enabled element in document order,
and move content focus to the previous enabled
element in document order (checkpoints 9.3 and
9.7);
- activate the link designed by the
content focus (checkpoints 1.1 and
9.1);
- search for text, search again for same text (checkpoint 9.8);
- increase the scale of rendered text, and
decrease the scale of rendered text (checkpoint 4.1);
- increase global volume, and decrease global volume (checkpoint 4.7);
- stop, pause, resume, and navigate efficiently selected audio and animations, including video and animated
images (checkpoint
4.5).
- If the user agent supports the following functionalities, the
default input configuration must also include bindings for them:
- next history state (forward), and previous history state (back);
- enter URI for a new resource;
- add a URI to favorites (i.e., bookmarked resources);
- view favorites;
- reload a resource;
- interrupt a request to reload a resource;
- for graphical viewports: navigation forward and backward through rendered
content by approximately the height of the viewport;
- for user agents that render content in lines of (at least) text: move point
of regard to next line, and previous line.
- The user agent may satisfy the functionality of entering a URI for a new
resource in a number of ways, including by prompting the user or by moving the
user interface focus to a control for entering
URIs.
Note: This checkpoint does not make any requirements about
the ease of use of default input configurations, though clearly the default
configuration should include single-key bindings and allow easy operation. Ease
of use is addressed by the configuration requirements of checkpoint 11.3.
Who benefits
- Users with blindness, some users with a physical disability, and some users
with a memory or cognitive disability.
Example techniques
- Input configurations should allow quick and direct navigation that does not
rely on graphical output. Do not require the user
to navigate through a graphical user interface as the only way to activate a
functionality.
Related techniques
- See the techniques of checkpoint 7.4 for information about indicating input
configurations.
Doing more
- Provide different input configuration profiles
(e.g., one keyboard profile with key combinations close together and another
with key combinations far apart).
- Offer a mode that makes the input configuration compatible with other
versions of the software (or with other software).
- Provide convenient bindings for controlling the user interface, such as
showing, hiding, moving, and resizing graphical
viewports.
- Allow the user to configure how much the viewport should move when
scrolling the viewport backward or forward through content (e.g., for a
graphical viewport, "page down" causes the viewport to move half the height of
the viewport, or the full height, or twice the height, etc.).
-
For the configuration requirements of this document, allow the user to save
user preferences in at least one user profile.
-
Allow the user to choose from among available user agent default profiles, profiles created by the same user,
and no profile (i.e., the user agent default settings).
- This checkpoint does not require the user agent to provide multiple default
profiles.
- This checkpoint does not require that user profiles be portable, i.e.,
removable from the user agent to be reread by a different instance of the
agent. Portable user profiles are very useful, however.
- Conformance detail: For user
agent features.
Notes and rationale
- The user agent is only expected to allow the user to choose from profiles
created by the same user, not profiles created by other users.
Who benefits
- Users with blindness, some users with a physical disability, and some users
with a memory or cognitive disability.
Example techniques
- Follow applicable operating
environment conventions for input configuration
profiles.
- Allow users to choose a different profile, to switch rapidly between
profiles, and to return to the default input configuration.
- If the user can edit the profile by hand, the user agent documentation
should explain the profile format.
Doing more
- If the user agent offers a way to restore the user agent default
configuration (e.g,. by pushing a button), prompt the user to save the current
configuration before restoring the default configuration. This scenario
illustrates the value of named, persistent, reloadable configurations.
- For graphical user agent user interfaces
with tool bars, allow the user to configure the position of user agent user interface
controls on those tool bars.
- Offer a predefined set of controls that
may be added to or removed from tool bars.
- Allow the user to restore the default
tool bar configuration.
Who benefits
- Users with serial access to content or who navigate sequentially, and some
users with a memory or cognitive disability (who may have difficulty
remembering where and how to access user agent functionalities).
Example techniques
- Use conventional operating
environment mechanisms for allowing configuration of font sizes,
synthesized speech rates, and other style parameters.
- Allow the user to show and hide user interface controls. This benefits
users with cognitive disabilities and users with
serial access to content or who navigate sequentially to user
interface controls.
- Allow the user to choose icons and/or text.
- Allow the user to change the grouping of icons and the order of menu
entries (e.g., for faster access to frequently used user interface
controls).
- Allow multiple icon sizes (big, small, other sizes). Ensure that these
values are applied consistently across the user interface.
- Allow the user to change the position of tool bars, icons, etc. Do not rely
solely on drag-and-drop for reordering the tool bar. Allow the user to
configure the user agent user interface
in a device-independent manner (e.g., through a text-based profile).
12.1 Provide accessible documentation.
(P1)
Checkpoint 12.1
-
Ensure that at least one version of the user agent
documentation conforms to at least level Double-A of the Web Content
Accessibility Guidelines 1.0 [WCAG10].
Notes and rationale
- User agents may provide documentation in many formats, but at least one
must conform to at least level Double-A of the Web Content Accessibility
Guidelines 1.0
[WCAG10].
- Remember to keep documentation accessible as the user agent evolves (e.g.,
when bug fixes are published, etc.).
Who benefits
- Many users with many types of disabilities.
Example techniques
- Distribute accessible documentation over the Web, on CD-ROM, or by recorded
voice. Alternative hardcopy formats may also benefit some users.
- For example, for conformance to the Web Content Accessibility Guidelines
1.0
[WCAG10]:
- Provide text equivalents of all non-text content (e.g., graphics, audio-only
presentations);
- Provide extended descriptions of screen-shots, flow charts, etc.;
- Provide a text equivalent for audio user agent
tutorials. Tutorials that use synthesized speech to guide a user through the
operation of the user agent should also be available at the same time as graphical representations.
- Use clear and consistent navigation and search mechanisms;
- Use the
NOFRAMES
element when the support/documentation is
presented in a FRAMESET
;
- Describe the user interface with device-independent terms. For example, use
"select" instead of "click on".
- Provide documentation in small chunks (for rapid downloads) and also as a
single source (for easy download and/or printing). A single source might be a
single HTML file or a compressed archive of several
HTML documents and included images.
- Ensure that run-time help and any Web-based help or support information is
accessible and may be operated with a single, well-documented, input command
(e.g., key stroke). Use operating environment
conventions for input configurations related to run-time help.
- Ensure that user agent identification codes are accessible to users so they
may install their software. Codes printed on software packaging may not be
accessible to people with visual disabilities.
Doing more
- Provide accessible documentation for all audiences: end users, developers,
etc. For instance, developers with disabilities may wish to add accessibility
features to the user agent, and so require information on available APIs and
other implementation details.
- Provide documentation in alternative formats such as braille (refer to
"Braille Formats: Principles of Print to Braille Transcription 1997"
[BRAILLEFORMATS]), large print, or audio tape. Agencies such as
Recording for the Blind and Dyslexic [RFBD] and the (USA) National Braille
Press [NBP]
can create alternative formats.
12.2 Document accessibility features.
(P1)
Checkpoint 12.2
-
Document all user agent features that benefit accessibility.
- The user agent may satisfy this checkpoint either by
- providing a centralized view of the accessibility features, or
- integrating accessibility features into the rest of the documentation.
A centralized view is sufficient to satisfy this checkpoint and required to
satisfy checkpoint
12.5.
- For the purposes of this checkpoint, a user agent feature that benefits
accessibility is one implemented to satisfy the requirements of this document
(including the requirements of checkpoints 8.1 and 7.3, and the API requirements of
guideline 6).
- Conformance detail: For user
agent features.
Note: The help system should include discussion of user
agent features that benefit accessibility. The user agent should satisfy this
checkpoint by providing both centralized and integrated views of accessibility
features in the documentation.
Who benefits
- Many users with many types of disabilities.
Example techniques
- Document any features that affect accessibility and that depart from system
conventions.
- Provide a sensible index to accessibility features. For instance, users
should be able to find "How to turn off blinking text" in the documentation
(and the user interface). The user agent may support this feature by turning
off scripts, but users should not have to guess (or know) that turning off
scripts will turn off blinking text.
- Document configurable features in addition to defaults for those
features.
- Document the features implemented to conform with these guidelines.
- Include references to accessibility features in both the table of contents
and index of the documentation.
- If configuration files are used to satisfy the requirements of this
document, the documentation should explain the configuration file formats.
- In developer documentation, document the APIs that are required by this
document; see the API requirements of guideline 6.
References
- Apple publishes a list of Macintosh Accessibility Features
[MAC-ACCESS].
- Linux users may consult the "Linux Accessibility HOWTO"
[ACCESSIBILITY-HOWTO].
-
Document the default user agent input configuration (e.g., the
default keyboard bindings).
- If the user agent does not allow the user to override the default user
agent input configuration (see
checkpoint 11.3), the documentation used to satisfy this checkpoint also
satisfies checkpoint
11.1.
Note: Documentation should warn the user whenever the
default input configuration is inconsistent with conventions of the operating
environment.
Notes and rationale
- Documentation of keyboard accessibility is particularly important to users
with visual disabilities and some types of physical disabilities. Without this
documentation, a user with a disability (or multiple disabilities) may not
think that a particular task can be performed. Or the user may try to use a
much less efficient technique to perform a task, such as using a mouse, or
using an assistive technology's mouse emulation through key strokes.
Who benefits
- Many users with many types of disabilities.
Example techniques
- If the user agent inherits default values (e.g,. for the input
configuration and for highlight styles) from the operating environment,
document how to modify them in the operating environment, or explain where to
find this information in the documentation for the operating environment.
References
- As an example of online documentation of keyboard support, refer to the Mozilla
Keyboard Planning FAQ and Cross Reference for the Mozilla browser
[MOZILLA].
12.4 Document changes between versions.
(P2)
Checkpoint 12.4
-
Document changes from the previous version of the user agent to features
that benefit accessibility, including features of the user interface.
Notes and rationale
- In particular, document changes to the user interface.
Who benefits
- Many users with many types of disabilities.
Example techniques
- Either describe the changes that affect accessibility in the section of the
documentation dedicated to accessibility features (see checkpoint 12.5) or link
to the changes from the dedicated section.
- Provide a text description of changes (e.g., in a README file).
12.5 Provide dedicated accessibility section. (P2)
Checkpoint 12.5
- Provide a centralized view of all
features of the user agent that benefit accessibility, in a dedicated section
of the documentation.
- A centralized view is required to satisfy this checkpoint and sufficient to
satisfy checkpoint
12.2.
Note: Developers are encouraged to integrate descriptions
of accessibility features into the documentation alongside other features, in
addition to providing a centralized view.
Who benefits
- Many users with many types of disabilities.
Example techniques
- Integrate information about accessibility features throughout the
documentation. The dedicated section on accessibility should provide access to
the documentation as a whole rather than standing alone as an independent
section. For instance, in a hypertext-based help system, the section on
accessibility may link to pertinent topics elsewhere in the documentation.
- Ensure that the section on accessibility features is easy to find.
This section presents general techniques that may be relevant to more than
one checkpoint. This section is not written in terms of the requirements of the
checkpoints. Instead, it is organized according to other topics that should
also be familiar to user agent designers.
User agents need to ensure that users have access to content,
either rendered through the user interface
or made available to assistive technologies through an API. While
providing serial access to a stream of content
would satisfy this requirement, this would be analogous to offering recorded
music on a cassette: other technologies exist (e.g., CD-ROMs) that allow direct
access to music. It is just as important for user agents to allow users to
access Web content efficiently, whether the content is being rendered as a
two-dimensional graphical layout, an audio stream, or
series of lines of braille. Providing efficient access to content involves:
- Preserving structure when rendering;
- Allowing the user to select specific content and query its structure or
context (what am I examining?);
- Using and generating metadata to provide context (where am I?).
These topics are addressed below.
Note: Throughout this document, the term refers to a user
interaction mechanism whereby:
- The user designates a piece of content (e.g., with the selection or
focus).
- The user invokes a menu (e.g., through a keyboard shortcut) consisting of
options determined by the context selected by the user. For instance, if the
user has selected an HTML table cell, the context menu might offer information
about associated headers.
When used properly, markup languages structure content in ways that allow
user agents to communicate that structure across different renderings. A table
describes relationships among cells and headers. Graphically, user agents
generally render tables as a two-dimensional grid. However, relationships also
have to be apparent for users with
serial access to content or who navigate sequentially,
otherwise users may not understand the purpose of the table and the
relationships among its cells (see the section on
table techniques). User agents need to render content in ways that allow
users to understand the underlying document structure, which may consist of
headings, lists, tables, synchronized multimedia, link relationships, etc.
Providing alternative renderings (e.g., an outline view) will also help users
understand document structure.
Note: Even though the structure of a language like HTML may
be defined by a document type definition (DTD) or a schema,
user agents may convey structure according to a "more intelligent" document
model when that model is well-known. For instance, in the
HTML 4
[HTML4] and XHTML 1.0 [XHTML10] DTDs, heading elements
(H1 - H6) do not nest, but presenting the document as nested headings may
convey the document's structure more effectively than as a flat list of
headers.
The guidelines emphasize the importance of navigation as a way to provide
efficient access to content. Navigation allows users to access content more
efficiently and, when used in conjunction with
selection and focus mechanisms, allows users to query content
for metadata. For instance, blind users often navigate a document by skipping
from link to link, deciding whether to follow each link based on metadata about
the link. User agents can help them decide whether to follow a link by allowing
them to query each focused link for the link text, title information,
information about whether the link has been visited, etc. While much of this
information may be rendered, the information has to also be available to
assistive technologies.
For example, the Amaya browser/editor [AMAYA] makes available all attributes and their values to the user
through a context menu. The user selects an element
and opens an attribute menu that shows which attributes are available for the
element and which have been assigned values. The user may read or write values
to attributes (since Amaya is an editor as well as a browser). Information
about attributes is also available through Amaya's structured view, which
renders the document tree as structured text.
The selection may be widened (moved to the nearest node one level up the
document tree) by pressing the Escape key; this is a form of
structured navigation based on the underlying
document object model.
Users may want to select content based on structure alone (as offered by
Amaya) but also based on how the content has been rendered. For instance, most
user agents allow users to select ranges of rendered text that may cross
"element boundaries" (e.g., to select part of a paragraph that includes a
phrase that is emphasized).
Authors and user agents provide context to users through content, structure,
navigation mechanisms, and query mechanisms. Titles, dimensions, dates,
relationships, the number of elements, and other metadata all help orient the
user, particularly when available as text. For instance, user agents can help
orient users by allowing them to request that document headings and lists be
numbered. See also the section on table
techniques, which explains how user agents can offer table navigation and
the ability to query a table cell for information about the cell's row and
column position, associated header information, etc.
- User agents can use style sheet languages such as CSS 2 [CSS2] and XSLT
[XSLT] to
generate context information (see techniques for
generated content).
- For information about elements and attributes that convey metadata in HTML,
refer to the index of elements and attributes in "Techniques for Web Content
Accessibility Guidelines 1.0" [WCAG10-TECHS].
- For information about elements and attributes that convey metadata in SMIL,
refer to the index of attributes in the W3C Note "Accessibility Features of
SMIL"
[SMIL-ACCESS].
- Describe a selected element's position within larger structures (e.g.,
numerical or relative position in a document, table, list, etc.). For example:
tenth link of fifty links; document heading 3.4; list one of two, item 4.5;
third table, three rows and four columns; current cell in third row, fourth
column; etc. Allow users to get this information on demand (e.g., through a
keyboard shortcut). Provide this information on the status line on demand from
the user.
To ensure accessibility, users need to be able to configure the style of rendered content and the user
interface. Author-specified styles, while important, may make content
inaccessible to some users. User agents need to allow users to increase the
scale of rendered text, to change colors and color combinations,
to slow down multimedia presentations, etc.
Cascading Style Sheets (CSS, defined in [CSS1] and [CSS2]) give authors
design flexibility and allow users to control important aspects of content
style; see checkpoint
4.14 for information about allowing users to choose from among available
style sheets. CSS includes mechanisms for tailoring rendering for a particular
output medium, including audio, braille, screen, and print.
- User agents should implement the
cascade order of CSS 2 ([CSS2], section 6.4.1) not CSS 1. In
CSS 2, user style sheets with
"!important" declarations (section 6.4.2) take precedence over author styles. Refer also to Web
Content Accessibility Guidelines 1.0 checkpoint 3.3 [WCAG10] for
content requirements related to style sheets.
- CSS-enabled user agents should consider as part of the cascade the markup
used for style, giving it a lower weight than actual style sheets. This allows
authors to specify style through markup for older user agents and to use more
powerful style sheets for CSS-enabled user agents. Refer to the section on the
precedence of non-CSS presentational hints in CSS 2 ([CSS2], section
6.4.4).
- To hide the CSS syntax from the user, user agents may implement user style
sheets through the user agent user interface.
User agents can generate a user style sheet from user preferences or behave as
though it did. Amaya [AMAYA] provides a GUI-based interface to create and
apply internal style sheets. The same technique may be used to control a user
style sheet.
- In JavaScript, the following may be used to change style information:
document.all.myElement style.color = "red";
User agents make links accessible by providing navigation to links, helping
users decide whether to follow them, and allowing interaction in a
device-independent manner. Link techniques include the following:
- See sequential navigation techniques for
information about navigating to links.
- When the user follows a link where the URI has a fragment identifier (e.g.,
"#chap1"), render the beginning of the target fragment at the top of the
viewport (not at the bottom, even if closer). Note: This technique applies to
formats like HTML where the fragment identifier semantics are to identify a
piece of content.
- Provide a link view that lists all links in the document. Allow the user to
configure how the links are sorted (e.g., by document order, sequential navigation order,
alphabetical order, visited or unvisited or both, internal or external or both,
etc.).
- Help the user remember links by including metadata in the link view. For
example, identify a selected link as "Link X of Y", where "Y" is the total
number of links. Lynx
[LYNX] numbers each link and provides information about the relative
position in the document. Position is relative to the current page and the
number of the current page out of all pages. Each page usually has 24
lines.
- Allow the user to configure how much information about a link to present in
the content view (when a link receives focus). For
instance, allow the user to choose between "Display links using hyperlink text"
or "Display links by title (if present)", with an option to toggle between the
two views. For a link without a title, use the link text.
- Here is a sample algorithm for ensuring that an HTML link that has image
content has associated text.
- If the author has specified conditional content (that is not
empty content) for the image (e.g.,
"alt" in HTML), use that as the link text;
- Otherwise, use the link title if available;
- [Repair] Otherwise, use title information of the designated Web resource (e.g., the TITLE element of
HTML for links to HTML documents).
- [Repair] Otherwise, render part of the filename or URI of the designated Web resource.
- [Repair] Otherwise, insert a generic text
placeholder (e.g., [LINK]) in place of the image (if configured to do
so).
- For an image in link content, ensure that the user has access to the link
and any long description associated with the
image.
User agents can make lists accessible by ensuring that list structure
– and in particular, embedded list structure – is available through
navigation and rendering.
- Allow users to turn on "contextual" rendering of lists (even for unordered
"bullet" lists). Use compound numbers (or letters, numbers, etc.) to introduce
each list item (e.g., "1, 1.1, 1.2, 1.2.1, 1.3, 2, 2.1"). This provides more
context and does not rely on the information conveyed by a graphical rendering,
as in:
1.
1.
2.
1.
3.
2.
1.
which might be serialized for synthesized speech or braille as "1, 1, 2, 1,
2, 3, 2, 1".
- Specify list numbering styles in CSS. Refer to the section generated
content, automatic numbering, and lists in CSS ([CSS2], section 12).
Example.
The following CSS 2 style sheet (taken from CSS
2, section 12.5) 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.
<STYLE type="text/css">
UL, OL { counter-reset: item }
LI { display: block }
LI:before { content: counters(item, ".");
counter-increment: item }
</STYLE>
End example.
The HTML TABLE element was designed to represent
relationships among data ("data" tables). Even when authored well and used
according to format specification, tables may pose problems for users with
disabilities for a number of reasons:
- Users who have serial access to content
or who navigate sequentially to a a
table may have difficulty grasping the relationships among cells, especially
for large and complex tables.
- Users with cognitive disabilities may have trouble grasping or remembering
relationships between cells and headers, especially for large and complex
tables.
- Users of screen magnifiers or with physical disabilities may have
difficulties navigating to the desired cells of a table.
For these situations, user agents may assist these users by providing table
navigation mechanisms and supplying context that is present in a
two-dimensional rendering (e.g., the cells surrounding a given cell).
To complicate matters, many authors use tables to lay out Web content
("layout" tables). Not only are table structures used to arrange objects
horizontally and vertically on the screen, table elements such as TH (table
header) in HTML are used to change the style of text (as table headers are
often rendered in bold fonts) rather than to indicate a true table header.
These practices make it difficult for assistive technologies to rely on markup
to convey document structure. Consequently, assistive technologies often resort
to interpreting the rendered content,
even though the rendered content has "lost" information encoded in the markup.
For instance, when an assistive technology "reads" a table from its graphical
rendering, the contents of multiline cells may become intermingled. For
example, consider the following table:
This is the top left cell This is the top right cell
of the table. of the table.
This is the bottom left This is the bottom right
cell of the table. cell of the table.
Screen readers that read rendered content line by line would read the table
cells incorrectly as "This is the top left cell This is the top right cell". So
that assistive technologies are not required to gather incomplete information
from renderings, these guidelines require that user agents provide access to content through an API (see checkpoint 6.3).
The following sections discuss techniques for providing improved access to
tables.
Users with serial access to content or who navigate sequentially cannot
gather information "at a glance" about a two-dimensional table. User agents can
make tables more accessible by providing the user with table metadata such as
the following:
- The table caption (the
CAPTION
element in HTML) or summary
information (the "summary
" attribute in HTML).
- The number of column groups and columns. Note that the number of columns
may change according to the row. Also, some parts of a table may have more than
two "dimensions." Project dimensionality higher than two onto two when
rendering information.
- The number of row groups and rows, in particular information about table
headers and footers.
- Which rows contain header information (whether at the top or bottom of the
table).
- Which columns contain header information (whether at the left or right of
the table).
- Whether there are subheads.
- How many rows or columns a header spans.
When navigating, quick access to table metadata will allow users to decide
whether to navigate within the table or skip over it. Other techniques:
- Allow users to query table summary information from inside a cell.
- Allow the user to choose different levels of detail for the summary (e.g.,
brief table summary and a more detailed summary).
- Allow the user to configure navigation so that table metadata is not
(re-)rendered each time the user enters the table.
A linear rendering of tables – cells presented one at a time, row by
row or column by column – may be useful, but generally only for simple
tables. For more complex tables, user agents need to convey more information
about relationships among cells and their headers. A linear rendering of a
table may be useful as an equivalent for a multi-dimensional table.
Note: The following techniques apply to columns as well as
rows. The elements listed in this section are HTML
4.01 table elements ([HTML4], section 11).
- Provide access to one row (
TR
) at a time, beginning with any
column header (TH
). If a header is associated with more than one
row, offer that header for each row concerned.
- Render cells (
TD
) with their associated headers. Allow the
user to configure how often headers are rendered (e.g., by implementing the
'speak-header
' property in CSS 2 [CSS2], section 17.7.1). Note also
that
the "abbr
" attribute in HTML 4 specifies
abbreviated headers for synthesized speech and other rendering ([HTML4], section
11.2.6). See also information about cell headers
later in this section.
- Provide access to cell content as marked up in the document source.
- Refer to techniques for authoring accessible tables in "Techniques for Web
Content Accessibility Guidelines 1.0" [WCAG10-TECHS].
The most important aspect of rendering a table cell is that the cell's
contents be rendered faithfully and be identifiable as the contents of a single
cell. However, user agents may provide additional information to help orient
the user:
- Render the row and column position of the cell in the table.
- Indicate how many rows and columns a cell spans.
- Since the contents of a cell in a data table may only be comprehensible in
context (i.e., with associated header information, row/column position,
neighboring cell information etc.), allow users to navigate to cells and query
them for this information.
- For HTML tables, refer to the
section on associating header information with data cells of
HTML 4 ([HTML4], section 11.4.1).
- In a table with a leading row and column of
TH
cells, the
interpretation of the corner cell as an
empty TD
or TH
should not contribute to the set
of headings for cells in that row and column.
- For nested tables, render information about the level of nesting.
- Since a cell may belong to N different dimensions in a multi-dimensional
table, provide information about headers from each dimension.
Properly constructed data tables distinguish header cells from data cells.
How headers are associated with table cells depends on the markup language. The
following algorithm is based on the
HTML 4.01 algorithm to calculate header information ([HTML4], section
11.4.3). For the sake of brevity, it assumes a left-to-right ordering, but will
also work (with minor modifications) for right-to-left tables (refer to the
"dir
" attribute of HTML 4 [HTML4], section
8.2). For a given cell:
- Search left from the cell's position to find row header (
TH
)
cells. Then search upwards from the cell's position to find column header
cells. The search in a given direction stops when the edge of the table is
reached or when a data cell is found after a header cell. If no headers are
found in either direction (left or up), search in the other directions (right
or down).
- Allow the user to configure where the header text comes from. For example,
in HTML 4, either the header cell element's content or the value of the
"
abbr
" attribute value ([HTML4], section 11.2.6).
- Insert row headers into the list in the (left-to-right) order they appear
in the table. Include values implicitly resulting from header cells in prior
rows with
rowspan="R"
, sufficient to extend into the current
row.
- Insert column headers after row headers, in the (top-to-bottom) order they
appear in the table. Include values implicitly resulting from header cells in
other columns with
colspan="C"
, sufficient to extend into the
current column containing the TD
cell.
- If a header cell has a value for the "headers" attribute, then insert it
into the list and stop the search for the current direction.
- Treat cells with a value for the "axis" attribute as header cells.
- Be sure to take into account header cells that span several rows or
columns.
Not all data tables include proper header markup, which the user agent may
be able to detect. Some repair strategies for finding header information
include the following:
- Consider that the top or bottom row contains header information.
- Consider that the leftmost or rightmost column in a column group contains
header information.
- If cells in an edge row or column span more than one row or column,
consider the following row or column to contain header information as
well.
- When trying to guess table structure, present several solutions to the
user.
Other repair issues to consider:
- Consider
TH
cells on both the left and right of the
table.
- For
TH
cells with "rowspan" set: consider the content of
those TH
cells for each of the N-1 rows below the one
containing that TH
content.
- An internal
TH
surrounded by TD
elements
makes it difficult to know whether the header applies to cells to its left or
right in the same row (or in both directions) or cells above or below it in the
same column (or in both directions).
- Finding column header cells assumes they are all above the
TD
element to which they apply.
- A
TH
element with "colspan
" set needs to be
included in the list of TH
elements for the N-1 columns to its
right.
To permit efficient access to tables, user agents should allow users to
navigate to tables and within tables, to select individual cells, and to query
them for information about the cell and the table as a whole.
- Allow users to navigate to a table, down to one of its cells, and back up
to the table level. This should work recursively for nested tables.
- Allow users to navigate to a cell by its row and column position.
- Allow users to navigate to all cells under a given header.
- Allow users to navigate row by row or column by column.
- Allow users to navigate to the cells around the current cell.
- Allow users to navigate to the first or last cell of a row, column, or the
table.
- Allow users to navigate from a cell directly to its related headers (if
it's possible to navigate to the headers).
- Allow the user to search for text content within a table
(i.e., without searching outside of the table). Allow the user to search for
text within specific rows or columns, row groups or column groups, or limited
by associated headers.
- Alert the user when the navigation reaches a table edge and when a cell
contains another table.
- Allow relative and direct navigation. For example, entering "-3, 20" might
mean "left three cells, up 20 cells").
- Allow navigation of table headers or footers only.
- Consider the issues raised by navigation to or from a cell that spans more
than one row or column.
- For examples of table navigation, refer to the table navigation script from
the Trace Research Center [TABLENAV].
One way to make an image map accessible to some users (e.g., users with
blindness) is to render the links it contains as text links. This allows
assistive technologies to render the links as synthesized speech or braille,
and benefits users with slow access to the Web and users of small Web devices
that do not support images but can support hypertext. User agents may allow
users to toggle back and forth between a graphical mode for image maps and a
text mode.
To construct a text version of an
image map in HTML:
- If the content of the
MAP element includes links, use them.
- Otherwise, for each
AREA
in the map, if (not empty conditional text content is
available (e.g., the "alt
" attribute), use it as the content of a
generated link.
- When the author has specified empty conditional text content
("
alt=''
"), do not render the link.
- When the author has specified no text equivalent (no "alt"), repair the
missing content per checkpoint
2.7.
Furthermore, user agents that render a text image map instead of an image
may preface the text image map with inline metadata such as:
- a string that announces the image map (e.g., "Start map")
- any conditional text content associated with the image (e.g., "alt" for
IMG).
- the number of links in the map.
Allow users to suppress, shrink, and expand text versions of image maps so
that they may quickly navigate to an image map (which may be, for example, a
navigation tool bar) and decide whether to "expand" it and follow the links of
the map. The metadata listed above will allow users to decide whether to expand
the map. Ensure that the user can expand and shrink the map and navigate its
links using the keyboard and other input devices.
HTML frames (see, for example, the
FRAME and
IFRAME elements in HTML 4 [HTML4]) were originally designed so
that authors could divide up graphic real estate and allow the pieces to change
independently (e.g., selecting an entry in a table of contents in one frame
changes the contents of a second frame). While frames are not inherently
inaccessible, they raise some accessibility issues:
- Equivalents to frame content. Some users cannot make use of frames because
they cannot grasp the (spatial or logical) relationships conveyed by frame
layout. Others cannot use them because their user agents or assistive
technology does not support them or makes access difficult (e.g., users with
screen readers or screen magnifiers).
- Navigation. Users need to be able to navigate from frame to frame in a
device independent manner.
- Orientation. Users need to know what frame they are in (so, for example,
authors should provide a title for each frame), what other frames are
available, and how the frames of a frameset are organized.
- Dynamic changes. Users need to know how the changes they cause in one frame
affect other frames.
To name a frame in HTML, use the following algorithm:
- Use the "
title
" attribute on FRAME
; or if not
present,
- Use the "
name
" attribute on FRAME
; or if not
present,
- Use title information of the referenced frame source (e.g., the
TITLE
element of the source HTML document); or
- Use title information of the referenced long description (e.g., what
"
longdesc
" refers to in HTML), or
- Use frame context (e.g., "Frame 2.1.3" to indicate the path to this frame
in nested framesets).
To make frames accessible, user agents should do the following:
- Make available conditional
content related to frames (e.g., provided by the
HTML 4 NOFRAMES element ([HTML4], section 16.4.1).
- Here is a technique for the case of a frameset that does not contain a
NOFRAMES
element but the individual frames have associated long
descriptions ("longdesc"):
- For each frameset, render the frameset title as an
H1
heading.
- For each frame, render the frame title in an
H2
heading,
followed by the content of the associated long description.
- Create a navigable table of contents according to the (possibly nested)
frameset structure. Each entry in the table of contents should link to a
frameset or frame. The end of the content used for each frame should include a
link back to this table of contents.
- Alert the user when the viewport contains a frameset.
- Render a frameset as a list of links to named frames so the user can
identify the number of frames. The list of links may be nested if framesets are
nested.
- Provide information about the number of frames in the frameset.
- Highlight the frameset with the current focus (e.g., by using a thick
border, by displaying the name of the frameset in the status bar).
- Allow the user to query the frame with the current focus for metadata about
the frame. Make available the frame title for speech synthesizers and braille
displays. Users may also use information about the number of images and words
in the frame to guess the purpose of the frame.
- Allow navigation between frames (forward and backward through the nested
structure, return to a top-level list of links to frames).
- Alert the user when an action in one frame causes the content of another
frame to change. Allow the user to navigate with little effort to the frame(s)
that changed.
- Authors can suppress scrolling of HTML frames with
scrolling="no"
.
- In order to ensure that content is accessible, allow the user to override
some attributes of the
FRAME element of HTML 4 ([HTML4], section 16.2.2):
"
noresize
", "scrolling
", and
"frameborder
".
The following screen shot illustrates how Home Page Reader [HPR] renders a
frameset by allowing the user to navigate (on the left side) to each of five
frames in a frameset.
The next screen shot illustrates how the user agent can provide information
about the number and structure of frames in the user agent user interface.
To make a form accessible, the user agent needs to ensure that:
- the user can navigate to all of the form elements;
- information about the form and its elements is available on demand;
- the user can interact with all form elements through the keyboard alone (or
voice alone or pointing device alone).
- Allow users to navigate to forms and to all controls within a form (refer
also to table navigation techniques). Opera
[OPERA]
and Navigator [NAVIGATOR] offer a number of
"form navigation" keyboard commands. When invoked, these "form navigation"
commands move the user agent's
current focus to the first form element (if any) in the document.
- If there are no forms in a document and the user attempts to navigate to a
form, alert the user.
- Provide a navigable, structured view of form elements (e.g., those grouped
by
LEGEND
or OPTGROUP
in HTML) along with their
labels.
- Allow the user to navigate away from a menu without selecting any option
(e.g., by pressing the Escape key).
Provide the following information about forms on demand:
- The number of forms in the document.
- The percentage of a form that has already been filled out. This will help
users who navigate
sequentially to form controls know whether they have completed the form.
Otherwise, users who encounter a submit button that is not the last control of
the form might inadvertently submit the incomplete form.
In conjunction with navigation:
- As the user navigates to a form element, provide information about whether
the control has to be activated
before form submission. For instance, in section 6.1.3 of XForms 1.0 [XFORMS10],
the
required property describes whether a value is required before the form's
instance data is submitted.
- For labels associated with form elements in markup (e.g., the
"
for
" attribute on LABEL
in HTML), make available
label information when the user navigates among the form elements.
- As the user navigates to a form element, provide information (e.g., through
context-sensitive help) about how the user can activate the element. Provide
information about what is required for each form element. Lynx [LYNX] conveys this
information by providing information about the currently selected form element
via a status line message:
- Radio Button: Use right-arrow or Return to toggle
- Checkbox Field: Use right-arrow or Return to toggle
- Option List: Press return and use arrow keys and return to select
option
- Text Entry Field: Enter Text. Use Up or Down arrows
or Tab to move off
- Textarea: Enter text. Up or Down arrows or
Tab to move off (^Ve for editor) Note: The
^Ve (caret-V, e) command, included in the
TEXTAREA
status line message, enables the user to invoke an external
editor defined in the local Lynx configuration file (lynx.cfg).
Provide the following information about the elements in a form on demand
(e.g., for the element with focus):
- Indicate the number of elements in the form.
- Indicate the number of elements that have not yet been completed.
- Provide a list of elements that have to be activated before form
submission.
- Provide information about the order of form elements (e.g., as specified by
"
tabindex
" in HTML). This is important since:
- Most forms are visually oriented, employing changes in font size and
color.
- Users who navigate
sequentially to form controls need to know they have supplied all the
necessary information before submitting the form.
- Provide information about which element has focus (e.g., "element X of Y
for the form named MyForm"). The form name is very important for documents that
contain more than one form. This will help users who navigate sequentially to form
controls know whether they have completed the form.
- Allow the user to query a form element for information about title, value,
grouping, type, status, and position.
- When a group of radio buttons receives
content focus, identify the radio button with content focus as "Radio
Button X of Y", where "Y" represents the total number of radio buttons in the
group. HTML 4 specifies the
FIELDSET
element ([HTML4], section 17.10), which
allows authors to group thematically related elements and labels. The
LEGEND
element ([HTML4], section 17.10) assigns a
caption to a FIELDSET
. For example, the LEGEND
element might identify a FIELDSET
of radio buttons as "Connection
Rate". Each button could have a
LABEL
element ([HTML4], section 17.9.1) stating a
rate. When it receives content focus, identify the radio button as "Connection
Rate: Radio button X of Y: 28.8kpbs", where "Y" represents the total number of
radio buttons in the grouping and "28.8kbps" is the information contained in
the LABEL
.
- Allow the user to invoke an external editor instead of editing directly in
a
TEXTAREA
element. This allows users to use all the features of
the external editor: macros, spell-checkers, validators, known input
configurations, autosave features, etc.
- Provide an option for transforming menus into checkboxes or radio buttons.
In the transformation, retain the accessibility information specified by the
author for the original form elements. Preserve the labels provided for the
OPTGROUP
and each individual OPTION
, and re-associate
them with the generated checkboxes. The LABEL
defined for the
OPTGROUP
should be converted into a LEGEND
for the
result FIELDSET
, and each checkbox should retain the
LABEL
defined for the corresponding OPTION
. Lynx [LYNX] does this for
HTML SELECT
elements that have the "multiple
"
attribute specified.
User agents may help orient users by generating additional content that
"announces" a context change. This may be done through CSS 2 [CSS2] style sheets
using a combination of selectors (including the
':before' and ':after' pseudo-elements described in section 12.1) and the
'content' property (section 12.2).
For instance, the user might choose to hear "language:German" when the natural language changes to German
and "language:default" when it changes back. This may be implemented in CSS 2
with the
':before' and ':after' pseudo-elements ([CSS2], section 5.12.3)
Example.
With the following definition in the style sheet:
[lang|=es]:before { content: "start Spanish "; }
[lang|=es]:after { content: " end Spanish"; }
the following HTML example:
<p lang="es" class="Spanish">
<a href="foo_esp.html"
hreflang="es">Esta pagina en español</a></p>
might be spoken "start Spanish _Esta pagina en espanol_ end Spanish". Refer
also to
information on matching attributes and attribute values useful for language
matching in CSS 2 ([CSS2], section 5.8.1).
The following example uses style sheets to distinguish visited from
unvisited links with color and a text prefix.
Example.
The phrase "Visited link:" is inserted before every visited link:
A:link { color: red } /* Unvisited links */
A:visited { color: green } /* Visited links */
A:visited:before { content: "Visited link: " }
To hide content, use the CSS
'display' or
'visibility' properties ([CSS2], sections 9.2.5 and 11.2,
respectively). The 'display' property suppresses rendering of an entire
subtree. The 'visibility' property causes the user agent to generate a
rendering structure, but the content is invisible.
The following XSLT style sheet (excerpted from the XSLT Recommendation
[XSLT],
Section 7.7) shows how one might number H4 elements in HTML
with a three-part label.
Example.
<xsl:template match="H4">
<fo:block>
<xsl:number level="any" from="H1" count="H2"/>
<xsl:text>.</xsl:text>
<xsl:number level="any" from="H2" count="H3"/>
<xsl:text>.</xsl:text>
<xsl:number level="any" from="H3" count="H4"/>
<xsl:text> </xsl:text>
<xsl:apply-templates/>
</fo:block>
</xsl:template>
End example.
When generating repair content, user
agent developers should consider the following issues:
- Some assistive technologies rely on an accurate mapping between the document object and what the
user agent renders. If repair content is not included in the document object,
but is used to determine rendering, there is likely to be a mismatch between
the two that may lead to confusion. User agent developers should therefore
consider including repair content in the document object. On the other hand,
some users may wish to leave the author's content unmodified, and others may
wish to have repair content included in the document object, but to be informed
about what was repaired.
- Repair content inserted in the document object
should conform to the Web Content Accessibility Guidelines 1.0 [WCAG10]. For
example, if the user agent inserts a graphical icon in the document object, that icon
should have a text equivalent: since the icon is
known to the user agent developer, the developer can provide a sensible text
equivalent to accompany it (for the benefit of users of assistive
technologies).
See also the section on table cell header repair
strategies. Refer also to the W3C document "Techniques for Authoring Tool
Accessibility Guidelines 1.0" [ATAG10-TECHS].
User agents need to make dynamic content accessible to users who may be
disoriented by changes in content, who may have a physical disability that
prevents them from interacting with a document within a time interval specified
by the author, or whose user agent does not support scripts or applets. Not only do user agents make
available equivalents to dynamic
content (e.g., audio, animations), they have to allow users to turn off
scripts, to stop animations, adjust timing parameters, etc.
Some user agents also allow users to turn off scripts for security reasons.
Certain elements of a markup language may have associated event handlers
that are activated when certain events occur. User agents need to be able to
identify those elements with event handlers statically associated (i.e.,
associated in the content, not in a script). In
HTML 4 ([HTML4], section 18.2.3),
intrinsic events are specified by the attributes beginning with the prefix
"on": "onblur
", "onchange
", "onclick
",
"ondblclick
", "onkeydown
", "onkeypress
",
"onkeyup
", "onload
", "onmousedown
",
"onmousemove
", "onmouseout
",
"onmouseover
", "onmouseup
", "onreset
",
"onselect
", "onsubmit
", and
"onunload
".
Techniques for providing access to scripts include the following:
- Allow the user to configure the user agent so that mouseover/mouseout event
handlers are activated by (and activate) focus/blur events. Similarly, allow
the user to use a key command, such as enter and
Shift-Enter to fire "
onclick
" and "ondblclick
"
events.
- Implement "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS] events with a single activation event and provide a
method for firing that event with each supported input device or input API.
These should be the same as the click events and mappings provided above (but
note that a user agent which is also an editor may wish to use single click
events for moving a system caret, and want to provide a different behavior to
activate using the mouse). For example, Amaya [AMAYA] uses a "doAction" command
for activating links and form elements, which can be activated either by the
mouse (and it is possible to set it for single-click or double-click) or by the
keyboard (it is possible to set it for any key using Amaya's keyboard
configuration)
- For authors: Document the effects of known important scripts to give users
an idea in advance of what they do. Do so by using the relevant elements or
attributes of the (markup language) specification, or if there aren't any, make
available a description of the script behavior.
When a user agent loads an Java applet, it should support the
Java system conventions for loading an assistive technology (see the appendix on loading assistive technologies for DOM
access). If the user is accessing the applet through an assistive
technology, the assistive technology should alert the user when the applet
receives content focus as this will likely
result in the launch of an associated plug-in or browser-specific Java Virtual
Machine. The user agent then needs to turn control of the applet over to the
assistive technology. User agents need to make conditional content available to
the assistive technology. Applets generally include an application frame that
provides title information.
User agents that allow users to modify default input configurations need to
account for configuration information from several sources: user agent
defaults, user preferences, author-specified configurations, and operating environment
conventions. Some examples include:
- Author: in HTML, the author may specify keyboard bindings with the
"accesskey" attribute ([HTML4], section 17.11.2).
- User: Users generally specify their preferences through the user interface
but may also do so programmatically or through a
profile.
- Operating environment: Users may specify preferred color contrasts at the
operating environment level.
To the user, the most important information is the final configuration once
all sources have been cascaded (combined) and all conflicts resolved. Knowing
the default configuration is also important; checkpoint 12.3 requires
that the default configuration be documented. The user may also want to know
how the current configuration differs from the default configuration and what
configuration in the viewport with the current focus comes from the author.
This information may also be useful to technical support personnel who may be
assisting users.
- The user interfaces for viewing and editing the input configuration may be
combined, but need not be. When a single interface is available to edit
bindings from any source, allow the user to apply filters to the list of
bindings (e.g., author-specified only, user agent default, user preference,
final configuration, etc.).
- The user interfaces for viewing and editing the input configuration need to
be accessible: do not rely on color alone to convey information, use
conventional user interface controls, allow
device-independent input and output, etc.
- In the user interface, associate with each binding a short text description
of the function to be activated. For example, if "Control-P" maps to
a print functionality, a short description might be "Print" or "Print setup".
For author-specified configurations, use available information (e.g., "title")
or use generic descriptions of what action will be taken(e.g., "Follow the link
with this link text").
- Allow users to query user interface controls for pertinent input
configuration information (e.g., what key will activate the
functionality).
In general, user preferences should override other configurations, however
this may not always be desirable. For example, users should be prevented from
configuring the user agent in a way that would interfere with important
functionalities such as quitting the user agent or reconfiguring it.
Some options for resolving conflicts:
- Allow author configurations to override other configurations and alert the
user when this happens.
- Do not allow author configurations to override other configurations. Alert
the user when an author-specified binding has been overridden and provide
access to the author-specified control through other means (e.g., an unused
binding, a menu, in a list of all author-specified bindings, etc.)
- Author-specified keyboard bindings in combination with the user agent's
native configuration may conflict with operating environment
conventions. For example, Internet Explorer [IE-WIN] in Windows uses the
Alt key as the Compose key for author-specified bindings. If
the author has specified a configuration with the characters "h" or
"f", this will interfere with the operating environment
conventions for accessing help and the file menu, respectively. In addition to
the previous two options for handling conflicts, the user agent may allow the
user to choose another Compose key (either globally or on a per-document
basis when conflicts are detected).
Refer to the section on
restricted functionality and conformance in UAAG 1.0 for more information
about limitations in functionality due to content.
The following techniques apply to user agents that render content as
synthesized speech.
- Since user agents that render content as synthesized speech do not always
pronounce it correctly, they should provide additional context to facilitate
understanding. Techniques include:
- Spelling words
- Indicating punctuation, capitalization, etc.
- Allowing users to repeat words alone and in context.
- Using auditory nuances – including pitch, articulation model, volume,
and orientation – to convey meaning the way fonts, spacing, and borders
do in graphical media.
- Generating context. For example, a user agent might speak the word "link"
before a link, "heading" before the text content of a heading or
"item 1.4" before a list item.
- Rendering text according in the appropriate natural language.
- User agents that synthesize speech should implement the CSS 2 aural style
sheet properties ([CSS2], section 19) to allow users to
configure synthesized speech rate, volume, and pitch.
- User agents that provide accessible solutions for images should, by
default, provide no information about images where the author has
provided empty conditional content associated
with the image, otherwise information may clutter the user's view of the
content and cause confusion. See checkpoints 2.7 and 2.8 for
more information about repair content.
- User agents may recognize different natural languages and be able to
render content according to language markup defined for a certain part of the
document. For instance, a screen reader might change the pronunciation of
spoken text according to the language definition. This is usually desired and
done according to the capabilities of the tool. Some specialized tools might
give some finer user control for the pronunciation as well.
- Switching natural languages for blocks of content may be more helpful than
switching for short phrases. In some language combinations (e.g., Japanese
being the primary and English being the secondary or quoted language), short
foreign language phrases are often well-integrated in the primary language.
Dynamic switching for these short phrases may make the content sound unnatural
and possibly harder to understand. User agents might allow users to choose
elements for which they want to be alerted.
- Announce different classes of links differently (see checkpoint 10.5). For instance,
announce links internal to a resource as being different from links to another
page in the same domain, from links to another domain, etc. Announce visited
links differently as well.
- The following techniques for speaking data tables are adapted from the
"Tape Recording Manual" produced by the (USA) National Braille Association
[NBA]:
- Read the title, source, captions and any explanatory
keys.
- Describe the structure of the table. Include the number of columns, the
headers of each column and any associated sub-columns, reading from left to
right (for left-to-right tables). The subhead is not considered a column. If
column heads have footnotes, read them following each header.
- Explain whether the table will be read by rows (horizontally) or by columns
(vertically). The horizontal reading is usual but, in some cases, the vertical
reading better conveys the content. On rare occasions it is necessary to read a
table both ways.
- Repeat the column headers with the figures under them for the first two
rows. If the table is long, repeat the headers every fifth row. Always repeat
them during the reading of the last row.
- Indicate the last row by saying, "and finally . . . " or "last row
..."
- At the completion of the reading say "End table X." If the table appeared
on a page other than the one you were recording, add "Returning to text on page
Y."
References:
- For more information about voice browser technology developed at W3C, refer
to "Voice Browsers: An introduction and glossary for the requirements drafts"
[VOICEBROWSER].
- For information about voice recognition and accessibility, refer to "Speak
to Write" [SPEAK2WRITE].
Users with serial access to content or who navigate sequentially to
content may have difficulty interacting with content in two-dimensional space (e.g., to move a pointing
device). Using the keyboard to move the pointing device may help some users,
but this technique usually requires a significant amount of visual feedback as
well as physical dexterity, both of which may not be possible for users with
some disabilities.
To illustrate ways to reduce dependency on spatial interactions, consider a
Web site for travel through Europe. The author provides a map of Europe and
allows users to select regions they wish to visit using a pointing device. This
type of application is very convenient to some users, but may be inaccessible
to others. Authors can design such content to place the emphasis on objects (in
this case European countries) rather than screen coordinates. In HTML, for
example, authors should use client-side image maps instead of server-side image
maps.
When this is done, the user agent can present the list of countries in an
alternative fashion (e.g., as a list of links or menu entries) for users who
may find it difficult to select countries with the pointing device. This type
of interface generally benefits all users (e.g., some users who may not
recognize countries by shape or flag, some users may prefer the keyboard, some
users may have images turned off, the text may be searched, etc.).
The following techniques may be considered when integrating accessibility
features and internationalization.
- Implement content negotiation so that users may specify language
preferences. Or allow the user to choose manually from among related resources
available in different languages.
- Consider operating
environment level natural language preferences as the user's default
language preference. However, take caution about sending HTTP Accept-Language
request headers ([RFC2616], section 14.4) based on
the operating environment preferences. First, there may be a privacy problem as
indicated in RFC 2616, section 15.1.4 "Privacy Issues Connected to Accept
Headers". Also, the operating environment may define only one language, while
the Accept-Language request header may include many languages in different
priorities. Setting Accept-Language to be the operating environment language
may prevent a user from receiving content from a server that does not have a
match for this particular language but does for other languages acceptable to
the user.
- Render characters with the appropriate directionality. Refer to the
"dir" attribute and the
BDO element in HTML 4 ([HTML4], sections 8.2 and 8.2.4,
respectively).
For more information about content internationalization, refer to W3C's
"Character Model for the World Wide Web" [CHARMOD] and the Unicode
Consortium's Unicode specification [UNICODE].
This matrix summarizes which checkpoints are expected to benefit users with
certain types of disabilities. For more information about types of
disabilities, assistive technologies, access strategies, and more, refer to
W3C's "How People with Disabilities Use the Web"
[PWD-USE-WEB].
- learning
- 4.4
- hard of hearing
- 1.3,
2.2, 2.5, 2.6,
4.1, 4.2, 4.3, 4.7, 4.12
- memory
- 9.4, 9.10, 10.4, 10.5,
11.1, 11.2, 11.3, 11.4, 11.5,
11.6, 11.7
- color deficiency
- 3.1, 4.3, 10.2, 10.3, 10.6
- low vision
- 2.2, 2.5,
2.7, 2.8, 2.9, 3.2, 3.3, 3.5, 4.1, 4.2,
4.4, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 5.1, 5.4,
9.1, 9.2,
9.3, 9.4, 9.7, 9.8, 9.10, 10.2, 10.3, 10.4, 10.5,
10.6
- seizure disorder
- 3.3, 3.4
- physical
- 1.1, 1.2, 2.4, 2.9, 2.10, 5.3, 5.5,
9.1,
9.2, 9.3, 9.4, 9.5,
9.6, 9.7,
9.8, 9.9, 9.10, 10.3, 10.4, 10.5,
11.1, 11.2, 11.3, 11.4, 11.5,
11.6, 11.7
- all
- 2.1, 2.3,
4.14, 6.1, 6.2,
6.3, 6.4, 6.5, 6.6,
6.7, 6.8,
6.9,
6.10, 7.1, 7.2,
7.3, 7.4, 8.1, 8.2,
12.1, 12.2, 12.3,
12.4, 12.5
- deafness
- 1.3,
2.2, 2.5, 2.6,
4.1, 4.2, 4.3,
4.6
- cognitive
- 2.6, 3.1, 3.2, 3.3, 3.5, 3.6,
4.2, 4.3, 4.4,
4.5, 4.6, 5.1,
5.2, 5.3, 5.4,
5.5, 9.4, 9.8,
9.10, 10.4, 10.5, 10.7, 11.1, 11.2, 11.3, 11.4, 11.5,
11.6, 11.7
- blindness
- 1.1, 1.2,
1.3, 2.2, 2.4,
2.5, 2.7, 2.8,
2.9, 2.10, 3.2, 3.3, 3.5, 4.4,
4.7, 4.8, 4.9, 4.10, 4.11, 4.12, 4.13, 5.1,
5.3, 5.4, 5.5,
9.1, 9.2,
9.3, 9.4, 9.5,
9.6, 9.7,
9.8, 9.9, 9.10, 10.2, 10.3, 10.4, 10.5,
10.6,
10.7, 11.1, 11.2, 11.3,
11.5, 11.6, 11.7
Several operating systems include built-in accessibility features designed
to assist individuals with disabilities. Despite operating systems differences,
the built-in accessibility features use a similar naming convention and offer
similar functionalities, within the limits imposed by each operating system (or
particular hardware platform). The following is a list of built-in
accessibility features common to several operating environments:
- StickyKeys
- StickyKeys allows users who have difficulties with pressing several keys
simultaneously to press and release in sequence each key of the
configuration.
- MouseKeys
- These allow users to move the mouse cursor and activate the mouse button(s)
from the keyboard.
- RepeatKeys
- RepeatKeys allows users to set how fast a key repeats ("repeat rate") when
the key is held pressed. It also allows users to control how quickly the key
starts to repeat after the key has been pressed ("delay until repeat"). Users
can also turn off key repeating.
- SlowKeys
- SlowKeys instructs the computer not to accept a key as pressed until it has
been pressed and held down for more than a user-configurable length of
time.
- BounceKeys
- BounceKeys prevents extra characters from being typed if the user bounces
(e.g., due to a tremor) on the same key when pressing or releasing it.
- ToggleKeys
- ToggleKeys provides an audible indication for the status of keys that have
a toggled state (keys that maintain status after being released). The most
common toggling keys include Caps Lock, Num Lock, and Scroll Lock.
- SoundSentry
- SoundSentry monitors the operating system and applications for sounds in
order to provide a graphical indication when a sound is being
played. Older versions of SoundSentry may have flashed the entire display
screen for example, while newer versions of SoundSentry provide the user with a
selection of options, such as flashing the viewport that has the current focus
or flashing the active window caption bar.
The next three built-in accessibility features are not as commonly available
as the above group of features, but are included here for completeness and
future compatibility.
- ShowSounds
- ShowSounds are user settings or software switches that cause audio messages
to be presented using both audio and graphics. Applications may use these
switches as the basis of user preferences.
- HighContrast
- HighContrast sets fonts and colors designed to make the screen easier to
read.
- TimeOut
- TimeOut turns off built-in accessibility features automatically if the
computer remains idle for a user-configurable length of time. This is useful
for computers in public settings such as a library. TimeOut might also be
referred to as "reset" or "automatic reset".
The next accessibility feature listed here is not considered to be a
built-in accessibility feature (since it only provides an alternative input
channel) and is presented here only for completeness and future
compatibility.
- SerialKeys
- SerialKeys allows a user to perform all keyboard and mouse functions from
an external assistive device (such as communication aid) communicating with the
computer via a serial character stream (e.g., through a serial port or
infra-red port) rather than or in conjunction with, the keyboard, mouse, and
other conventional input devices and methods.
The following accessibility features can be adjusted from the Accessibility
Options Control Panel:
- StickyKeys: modifier keys include Shift, Control, and
Alt.
- FilterKeys: grouping term for SlowKeys, RepeatKeys, and BounceKeys.
- MouseKeys
- ToggleKeys
- SoundSentry
- ShowSounds
- Automatic reset (term used for TimeOut)
- High Contrast
- SerialKeys
Additional accessibility features available in Windows 98:
- Magnifier
- Magnifier is a windowed, screen enlargement and enhancement program used by
people with low vision to magnify an area of the
graphical display (by tracking the text cursor,
current focus, etc.). Magnifier can also invert colors within the
magnification window.
- Accessibility Wizard
- The Accessibility Wizard is a setup tool to assist users with the
configuration of operating environment accessibility features.
References:
- To find out about built-in accessibility features on Windows platforms, ask
the operating system via the "SystemParametersInfo" function. Refer to
"Software accessibility guidelines for Windows applications"
[MS-ENABLE] for more information.
- For information about Microsoft keyboard configurations (Internet Explorer,
Windows 95, Windows 98, and more), refer to documentation on keyboard
assistance for Internet Explorer and MS Windows
[MS-KEYBOARD].
The following accessibility features can be adjusted from the Easy Access
Control panel. Note: The Apple naming convention for accessibility features is to put spaces between
the terms (e.g., "Sticky Keys" instead of "StickyKeys").
- Sticky Keys: modifier keys include the Shift, Command
(Open apple), Option (Alt), and
Control keys.
- Slow Keys
- Mouse Keys
The following accessibility features can be adjusted from the Keyboard
Control Panel.
- Key Repeat Rate (part of RepeatKeys)
- Delay Unit Repeat (part of RepeatKeys)
The following accessibility feature can be adjusted from the Sound or
Monitors and Sound Control Panel (depending on operating system version).
- Adjusting the volume to off or mute causes the Macintosh to flash the title
bar whenever the operating system detects a sound (e.g., SoundSentry)
Additional accessibility features available for the Macintosh OS:
- CloseView
- CloseView is a full screen, screen enlargement and enhancement program used
by people with low vision to magnify the information on the graphical display,
and it can also change the colors used by the operating system.
- SerialKeys
- SerialKeys is available as freeware from Apple and several other Web
sites.
The following accessibility features can be adjusted from the AccessX
graphical user interface X client on some DEC, SUN, and SGI operating systems.
Other operating systems supporting XKB may require command line
interaction.
- StickyKeys: modifier keys are platform-dependent, but usually include the
Shift, Control, and Meta keys.
- RepeatKeys
- SlowKeys
- BounceKeys
- MouseKeys
- ToggleKeys
Note: AccessX became a supported part of the X Window
System X Server with the release of the X Keyboard Extension in version
X11R6.1.
The following accessibility features are available from a freeware program
called AccessDOS, which is available from several Internet Web sites including
IBM, Microsoft, and the Trace Center, for either PC-DOS or MS-DOS versions 3.3
or higher.
- StickyKeys: modifier keys include the Shift, Control,
and Alt keys.
- Keyboard Response Group: grouping term for SlowKeys, RepeatKeys, and
BounceKeys
- MouseKeys
- ToggleKeys
- SoundSentry (incorrectly named ShowSounds)
- SerialKeys
- TimeOut
Many of the checkpoints in the guidelines require a "host" user agent to
communicate information about content and the user interface to assistive
technologies. This appendix explains how developers can ensure the timely
exchange of this information (see checkpoint 6.10). The techniques described here include:
- Loading the entire assistive technology in the
address space of the host user agent;
- Loading part of the assistive technology in the
address space of the host user agent (e.g., piece of stub code, a dynamically
linked library (DLL), a browser helper
object, etc.);
- Out-of-process access to the document object model.
The first two techniques are similar, differing in the amount of, or
capability of, the assistive technology loaded in the same process or address
space as the host user agent. These techniques are likely to provide faster
access to the document object model since
they will not be subject to inter-process communication overhead.
First, the host user agent needs to know which assistive technology to load.
One technique for this is to store a reference to an assistive technology in a
system registry file or, in the case of Java, a properties file. Registry files
are common among many operating environments:
- Windows: use the system registry file
- IBM OS/2: use the system.ini
- On client/server systems: use a system registry server that an application
running on the network client computer can query.
- In Sun Java 2, use the "accessibility.properties" file, which causes the
system event queue to examine the file for assistive technologies required for
loading. If the file contains a property called "assistive_technologies", it
will load all registered assistive technologies and start them on their own
thread in the Java Virtual Machine that is a single process.
Here is an example entry for Java:
assistive_technologies=com.ibm.sns.svk.AccessEngine
In Microsoft Windows, a similar technique could be followed by storing the
name of a Dynamic Link Library (DLL) for an assistive
technology in a designated assistive technology key name/assistive technology
pair.
Here is an example entry for Windows:
HKEY_LOCAL_MACHINE\Software\Accessibility\DOM
"ScreenReader, VoiceNavigation"
Once the assistive technology has been registered, any other user agent can
determine whether it needs to be loaded and then load it. Once loaded, the
assistive technology can monitor the document object
model as needed.
On a non-Java platform, a technique to do this would be to create a separate
thread with a reference to the document object model using a
DLL. This new thread will load the DLL and call a
specified DLL entry name with a pointer to the document object model interface.
The assistive technology process will then run as long as required.
The assistive technology has the option to either:
- communicate with a main assistive technology of its own and process the
document object model as a caching mechanism for the main assistive technology,
or
- act as a bridge to the document object model for the main assistive
technology.
In the future, it will be necessary to provide a more comprehensive
reference to the application that not only provides direct navigation to its
client area document object model, but also multiple document object models
that it is processing and an event model for monitoring them.
Java can facilitate timely access to accessibility components. In this
example, an assistive technology running on a separate thread monitors user
interface events such as focus changes. When focus
changes, the assistive technology is alerted of which component object has
focus. The assistive technology can communicate directly with all components in
the application by walking the parent/child hierarchy and connecting to each
component's methods and monitor events directly. In this case, an assistive
technology has direct access to component specific methods as well as those
provided for by the Java Accessibility API. There is no
reason that a document object model interface to user agent components could
not be provided via Java.
In Java 1.1.x, Sun's Java access utilities load an assistive by monitoring
the Java awt.properties file for the presence of assistive
technologies and loads them as shown in the following code example:
Example.
import java.awt.*;
import java.util.*;
String atNames =
Toolkit.getProperty("AWT.assistive_technologies",null);
if (atNames != null) {
StringTokenizer parser = new StringTokenizer(atNames," ,");
String atName;
while (parser.hasMoreTokens()) {
atName = parser.nextToken();
try {
Class.forName(atName).newInstance();
}
catch (ClassNotFoundException e) {
throw new AWTError("Assistive Technology not found: "
+ atName);
}
catch (InstantiationException e) {
throw new AWTError("Could not instantiate Assistive"
+ " Technology: " + atName);
}
catch (IllegalAccessException e) {
throw new AWTError("Could not access Assistive"
+ " Technology: " + atName);
} catch (Exception e) {
throw new AWTError("Error trying to install Assistive"
+ " Technology: " + atName + " " + e);
}
}
}
In the above code example, the function
Class.forName(atName).newInstance()
creates a new instance of the
assistive technology. The constructor for the assistive technology will then be
responsible for monitoring application component objects by monitoring system
events.
In the following code example, the constructor for the assistive technology,
AccessEngine
, adds a focus change listener using Java
accessibility utilities. When the assistive technology is alerted that an
object has received focus, it has direct access to that object. If the Object,
o
, has implemented a document object model interface, the
assistive technology will have direct access to the document object model in
the same process space as the application.
Example.
import java.awt.*;
import javax.accessibility.*;
import com.sun.java.accessibility.util.*;
import java.awt.event.FocusListener;
class AccessEngine implements FocusListener {
public AccessEngine() {
//Add the AccessEngine as a focus change listener
SwingEventMonitor.addFocusListener((FocusListener)this);
}
public void focusGained(FocusEvent theEvent) {
// get the component object source
Object o = theEvent.getSource();
// check to see if this is a dom component
if (o instanceof DOM) {
...
}
}
public void focusLost(FocusEvent theEvent) {
// Do Nothing
}
}
In this example, the assistive technology has the option of running
stand-alone or acting as a cache for a bridge that communicates with a main
assistive technology running outside the Java virtual machine.
In order to attach to a running instance of Internet Explorer 4.0, you can
use a Browser Helper Object ([BHO]), which is a DLL
that will attach itself to every new instance of Internet Explorer 4.0 [IE-WIN] (only
if you run iexplore.exe). You can use this feature to gain access to the object
model of Internet Explorer and to monitor events. This can be tremendously
helpful when many method calls need to be made to Internet Explorer, as each
call will be executed much more quickly than the out of process case.
There are some requirements when creating a Browser Helper Object:
- The application that you create must be an in-process server (that is,
DLL).
- This DLL must implement
IObjectWithSite
.
- The
IObjectWithSite::SetSite()
method must be implemented. It
is through this method that your application receives a pointer to Internet
Explorer's IUnknown
. Internet Explorer actually passes a pointer
to IWebBrowser2
but the implementation of SetSite()
receives a pointer to IUnknown
. You can use this
IUnknown
pointer to automate Internet Explorer or to sink events from
Internet Explorer.
- It must be registered as a Browser Helper Object as described above.
To provide native Microsoft Windows assistive technologies access to Java
applications without creating a Java native solution, Sun Microsystems provides
the "Java Access Bridge." This bridge is loaded as an assistive technology as
described in the section on loading assistive
technologies for direct navigation of the document object model. The bridge
uses a Java Native Invocation (JNI) to Dynamic Link Library
(DLL) communication and caching mechanism that allows a
native assistive technology to gather and monitor accessibility information in
the Java environment. In this environment, the assistive technology determines
that a Java application or applet is running and communicates with the Java
Access Bridge DLL to process accessibility information about
the application/applet running in the Java Virtual Machine.
Access to application specific data across process boundaries or address
spaces might be costly in terms of performance. However, there are other
reasons to consider when accessing the document object
model that might lead a developer to wish to access it from their own
process or memory address space. One obvious protection this method provides is
that, if the user agent fails, it does not disable the user's assistive
technology as well. Another consideration would be legacy systems, where the
user relies on their assistive technology for access to software other than the
user agent, and thus would have their application loaded all the time.
There are several ways to gain access to the user agent's document object model. Most
user agents support some kind of external interface, or act as a mini-server to
other applications running on the desktop. Internet Explorer [IE-WIN] is a
good example of this, as IE can behave as a component object model
(COM) server to other applications. Mozilla [MOZILLA], the
open source release of Navigator also supports cross-platform COM
(XPCOM).
The following example illustrates the use of COM to access the IE object
model. This is an example of how to use COM to get a pointer to the
WebBrowser2
module, which in turn enables access to an interface/pointer
to the document object, or IE document object model for the content.
Example.
/* first, get a pointer to the WebBrowser2 control */
if (m_pIE == NULL) {
hr = CoCreateInstance(CLSID_InternetExplorer,
NULL, CLSCTX_LOCAL_SERVER, IID_IWebBrowser2,
(void**)&m_pIE);
/* next, get a interface/pointer to the document in view,
this is an interface to the document object model (DOM)*/
void CHelpdbDlg::Digest_Document() {
HRESULT hr;
if (m_pIE != NULL) {
IDispatch* pDisp;
hr = m_pIE->QueryInterface(IID_IDispatch,
(void**) &pDisp);
if (SUCCEEDED(hr)) {
IDispatch* lDisp;
hr = m_pIE->get_Document(&lDisp);
if (SUCCEEDED(hr)) {
IHTMLDocument2* pHTMLDocument2;
hr = lDisp->QueryInterface(IID_IHTMLDocument2,
(void**) &pHTMLDocument2);
if (SUCCEEDED(hr)) {
/* with this interface/pointer, IHTMLDocument2*,
you can then work on the document */
IHTMLElementCollection* pColl;
hr = pHTMLDocument2->get_all(&pColl);
if (SUCCEEDED(hr)) {
LONG c_elem;
hr = pColl->get_length(&c_elem);
if (SUCCEEDED(hr)) {
FindElements(c_elem, pColl);
}
pColl->Release();
}
pHTMLDocument2->Release();
}
lDisp->Release();
}
pDisp->Release();
}
}
}
}
For a working example of this method, refer to HelpDB [HELPDB].
This glossary is normative. However, some
terms (or parts of explanations of terms) may not have an impact on
conformance.
Note: In this document, glossary terms generally link to
the corresponding entries in this section. These terms are also highlighted
through style sheets and identified as glossary terms through markup.
- Activate
- In this document, the verb "to activate" means (depending
on context) either:
The effect of activation depends on the type of the user interface control. For
instance, when a link is activated, the user agent generally retrieves the
linked Web resource. When a form element is
activated, it may change state (e.g., check boxes) or may take user input
(e.g., a text entry field).
-
Alert
- In this document, "to alert" means to make the user aware
of some event, without requiring acknowledgement. For example, the user agent
may alert the user that new content is available on the server by displaying a
text message in the user agent's status bar. See
checkpoint 1.3 for requirements
about alerts.
-
Animation
- In this document, an "animation" refers to content that, when rendered, creates a visual
movement effect automatically (i.e., without manual user interaction). This
definition of animation includes video and animated images. Animation
techniques include:
- graphically displaying a sequence of snapshots within the same region
(e.g., as is done for video and animated images). The series of snapshots may
be provided by a single resource (e.g., an animated GIF image) or from distinct
resources (e.g., a series of images downloaded continuously by the user
agent).
- scrolling text (e.g., achieved through markup or style sheets).
- displacing graphical objects around the viewport (e.g., a picture of a ball
that is moved around the viewport giving the impression that it is bouncing off
of the viewport edges). For instance, the SMIL 2.0 [SMIL20] animation modules explain
how to create such animation effects in a declarative manner (i.e., not by
composition of successive snapshots).
-
Applet
- An applet is a program (generally written in the Java
programming language) that is part of content,
and that the user agent executes.
- Application
Programming Interface (API), conventional input/output/device
API
- An application programming interface (API) defines how
communication may take place between applications.
Implementing APIs that are independent of a particular operating environment
(as are the W3C DOM Level 2 specifications) may reduce implementation costs for
multi-platform user agents and promote the development of multi-platform
assistive technologies. Implementing conventional APIs for a particular
operating environment may reduce implementation costs for assistive technology
developers who wish to interoperate with more than one piece of software
running on that operating environment.
A "device API" defines how communication may take place
with an input or output device such as a keyboard, mouse, video card, etc.
In this document, an "input/output API" defines how
applications or devices communicate with a user agent. As used in this
document, input and output APIs include, but are not limited to, device APIs.
Input and output APIs also include more abstract communication interfaces than
those specified by device APIs. A "conventional input/output API" is one that
is expected to be implemented by software running on a particular operating
environment. For example, on desktop computers today, the conventional input
APIs are for the mouse and keyboard. For touch screen
devices or mobile devices, conventional input APIs may
include stylus, buttons, voice, etc. The graphical display and sound card are
considered conventional output devices for a graphical desktop computer
environment, and each has an associated API.
- Assistive technology
- In the context of this document, an assistive technology
is a user agent that:
- relies on services (such as retrieving Web
resources, parsing markup, etc.) provided by one or more other "host" user
agents. Assistive technologies communicate data and messages with host user
agents by using and monitoring
APIs.
- provides services beyond those offered by the host user agents to meet the
requirements of users with disabilities. Additional services include
alternative renderings (e.g., as synthesized speech or magnified content),
alternative input methods (e.g., voice), additional navigation or orientation
mechanisms, content transformations (e.g., to make tables more accessible),
etc.
For example, screen reader software is an assistive technology because it
relies on browsers or other software to enable Web access, particularly for
people with visual and learning disabilities.
Examples of assistive technologies that are important in the context of this
document include the following:
- screen magnifiers, which are used by people with visual disabilities to
enlarge and change colors on the screen to improve the visual readability of
rendered text and images.
- screen readers, which are used by people who are blind or have reading
disabilities to read textual information through synthesized speech or braille
displays.
- voice recognition software, which may be used by people who have some
physical disabilities.
- alternative keyboards, which are used by people with certain physical
disabilities to simulate the keyboard.
- alternative pointing devices, which are used by people with certain
physical disabilities to simulate mouse pointing and button activations.
- Beyond this document, assistive technologies consist of
software or hardware that has been specifically designed to assist people with
disabilities in carrying out daily activities, e.g., wheelchairs, reading
machines, devices for grasping, text telephones, vibrating pagers, etc. For
example, the following very general definition of "assistive technology device"
comes from the (U.S.) Assistive Technology Act of 1998 [AT1998]:
Any item, piece of equipment, or product system, whether acquired
commercially, modified, or customized, that is used to increase, maintain, or
improve functional capabilities of individuals with disabilities.
-
Attribute
- This document uses the term "attribute" in the XML sense:
an element may have a set of attribute specifications (refer to the XML 1.0
specification
[XML] section 3).
-
Audio
- In this document, the term "audio" refers to content that
encodes prerecorded sound.
- Audio-only
presentation
- An audio-only presentation is content consisting
exclusively of one or more audio tracks presented
concurrently or in series. Examples of an audio-only presentation include a
musical performance, a radio-style news broadcast, and a narration.
-
Audio track
- An audio object is content rendered as sound through an
audio viewport. An audio track is an audio object
that is intended as a whole or partial presentation. An audio track may, but is
not required to, correspond to a single audio channel (left or right audio
channel).
- Audio description
- An audio description (called an "auditory description" in
the Web Content Accessibility Guidelines 1.0 [WCAG10]) is either a prerecorded
human voice or a synthesized voice (recorded or generated dynamically)
describing the key visual elements of a movie or other animation. The audio
description is synchronized with (and possibly included
as part of) the audio track of the presentation, usually
during natural pauses in the audio track. Audio
descriptions include information about actions, body language, graphics, and
scene changes.
-
Author styles
- Authors styles are style property
values that come from content (e.g., style sheets
within a document, that are associated with a document, or that are generated
by a server).
- Captions
- Captions are text transcripts that are synchronized with other audio tracks or
visual tracks. Captions convey information about spoken words and
non-spoken sounds such as sound effects. They benefit people who are deaf or
hard-of-hearing, and anyone who cannot hear the audio (e.g., someone in a noisy
environment). Captions are generally rendered
graphically superimposed ("on top of") the synchronized visual track.
The term "open captions" generally refers to captions that are always
rendered with a visual track; they cannot be turned off. The term "closed
captions" generally refers to captions that may be turned on and off. The
captions requirements of this document assume that the user agent can recognize the captions as such; see the
section on
applicability for more information.
Note: Other terms that include the word "caption" may have
different meanings in this document. For instance, a "table caption" is a title
for the table, often positioned graphically above or below the table. In this
document, the intended meaning of "caption" will be clear from context.
- Character encoding
- A "character encoding" is a mapping from a character set
definition to the actual code units used to represent the data. Refer to the
Unicode specification [UNICODE] for more information
about character encodings. Refer to "Character Model for the World Wide Web"
[CHARMOD] for additional information about characters and character
encodings.
- Collated text
transcript
- A collated text transcript is a text
equivalent of a movie or other animation. More specifically, it is the
combination of the text transcript of the
audio track and the text equivalent of
the visual track. For example, a collated
text transcript typically includes segments of spoken dialogue interspersed
with text descriptions of the key visual elements of a presentation (actions,
body language, graphics, and scene changes). See also the definitions of text transcript and audio description. Collated text
transcripts are essential for individuals who are deaf-blind.
- Conditional content
- Conditional content is content that, by format
specification, should be made available to users through the user interface,
generally under certain conditions (e.g., based on user preferences or
operating environment limitations). Some examples of conditional content
mechanisms include:
- The "
alt
" attribute of the IMG
element in HTML 4.
According to
section 13.2 of the HTML 4 specification ([HTML4]): "User agents must render
alternate text when they cannot support images, they cannot support a certain
image type or when they are configured not to display images.
OBJECT
elements in HTML 4.
Section 13.3.1 of the HTML 4 specification ([HTML4]) explains the conditional
rendering rules of (nested) OBJECT
elements. The rules select
among ordered alternatives according to user preferences or error
conditions.
- The
switch
element and test attributes in SMIL 1.0. Sections
4.3 and 4.4, respectively,
of SMIL 1.0
[SMIL] explain the conditional rendering rules of these
features.
- SVG 1.0
[SVG] also includes a
switch
element and several
attributes for conditional processing.
- The
NOSCRIPT
and NOFRAMES
elements in HTML 4
[HTML4]
allow the author to provide content under conditions when the user agent does
not support scripts or frames, or the user has turned off support for scripts
or frames.
Specifications vary in how completely they define how and when to render
conditional content. For instance, the HTML 4 specification includes the
rendering conditions for the "alt
" attribute, but not for the
"title
" attribute. The HTML 4 specification does indicate that the
"title
" attribute should be available to users through the user
interface ("Values of the title attribute may be rendered by user agents in a
variety of ways...").
Note: The Web Content Accessibility Guidelines 1.0 requires
that authors provide text equivalents for non-text content. This is generally
done by using the conditional content mechanisms of a markup language. Since
conditional content may not be rendered by default, the current document
requires the user agent to provide access to unrendered conditional content (checkpoint 2.3 and checkpoint 2.9)
as it may have been provided to promote accessibility.
-
Configure,
control
- In the context of this document, the verbs "to control"
and "to configure" share in common the idea of governance such as a user may
exercise over interface layout, user agent behavior, rendering style, and other
parameters required by this document. Generally, the difference in the terms
centers on the idea of persistence. When a user makes a change by
"controlling" a setting, that change usually does not persist beyond that user
session. On the other hand, when a user "configures" a setting, that setting
typically persists into later user sessions. Furthermore, the term "control"
typically means that the change can be made easily (such as through a keyboard
shortcut) and that the results of the change occur immediately. The term
"configure" typically means that making the change requires more time and
effort (such as making the change via a series of menus leading to a dialog
box, via style sheets or scripts, etc.). The results of "configuration" might
not take effect immediately (e.g., due to time spent reinitializing the system,
initiating a new session, rebooting the system).
In order to be able to configure and control the user agent, the user needs
to be able to "write" as well as "read" values for these parameters.
Configuration settings may be stored in a profile.
The range and granularity of the changes that can be controlled or configured
by the user may depend on limitations of the operating environment or
hardware.
Both configuration and control may apply at different "levels": across Web resources (i.e., at the user agent
level, or inherited from the operating environment), to the
entirety of a Web resource, or to components of a Web resource (e.g., on a
per-element basis).
A
global configuration is one that applies across elements of the
same Web resource, as well as across Web resources. A global configuration may
be implemented by more than one setting (e.g., per component of the user
agent). For instance, when a user agent consists of a browser that renders HTML
and a plug-in that renders SVG, to satisfy the global configuration
requirements of this document, the browser may provide one setting and the
plug-in another.
User agents may allow users to choose configurations based on various
parameters, such as hardware capabilities, natural language, etc.
Note: In this document, the noun "control" refers to a user interface control.
-
Content
- In this specification, the noun "content" is used in three
ways:
- It is used to mean the document object as a
whole or in parts.
- It is used to mean the content of an HTML or XML element, in the sense
employed by the XML 1.0 specification ([XML], section 3.1): "The text between
the start-tag and end-tag is called the element's content." Context should
indicate that the term content is being used in this sense.
- It is used in the terms non-text content and text content.
Empty
content (which may be conditional content) is either a
null value or an empty string (i.e., one that is zero characters long). For
instance, in HTML, alt=""
sets the value of the "alt
"
attribute to the empty string. In some markup languages, an element may have
empty content (e.g., the HR
element in HTML).
- Device-independence
- Device-independence refers to the ability to make use of
software with any appropriate supported input or output device.
-
Document object,
Document Object Model (DOM)
- In general usage, the term "document object" refers to the user agent's
representation of data (e.g., a document). This data generally comes from the
document source, but may also be
generated (from style sheets, scripts, transformations, etc.), produced as a
result of preferences set within the user agent, added as the result of a
repair performed automatically by the user agent, etc. Some data that is part
of the document object is routinely rendered (e.g., in HTML, what
appears between the start and end tags of elements and the values of attributes
such as "alt", "title", and "summary"). Other parts of the document object are
generally processed by the user agent without user awareness, such as DTD- or schema-defined names of
element types and attributes, and other attribute values such as "href", "id",
etc. These guidelines require that users have access to both kinds of data
through the user interface. Most of the requirements of this document apply to
the document object after its construction. However, a few checkpoints (e.g.,
checkpoint 2.7 and checkpoint 2.10) may
affect the construction of the document object.
A "document object model" is the abstraction that governs the construction
of the user agent's document object. The document object model employed by
different user agents may vary in implementation and sometimes in scope. This
specification requires that user agents implement the APIs defined
in Document Object Model (DOM) Level 2 specifications ([DOM2CORE]
and
[DOM2STYLE]) for access to HTML,
XML, and CSS content. These DOM APIs allow authors
to access and modify the content via a scripting language (e.g., JavaScript) in
a consistent manner across different scripting languages. As a standard
interface, the DOM APIs make it easier not just for authors, but for assistive
technology developers to extract information and render it in ways most suited
to the needs of particular users.
-
Document character set
- A document character set (a concept taken from SGML) is a
sequence of abstract characters that may appear in Web content represented in a
particular format (such as HTML, XML, etc.). A document character set consists
of:
- A "repertoire": A set of abstract characters, such as the Latin letter "A",
the Cyrillic letter "I", the Chinese character meaning "water", etc.
- Code positions: A set of integer references to characters in the
repertoire.
For instance, the character set required by the HTML 4 specification [HTML4] is defined
in the Unicode specification [UNICODE]. Refer to "Character
Model for the World Wide Web" [CHARMOD] for more information
about document character sets.
-
Document source, text source
- In this document, the term "document source" refers to the
data that the user agent receives as the direct result of a request for a Web resource (e.g., as the result of an
HTTP/1.1
[RFC2616] "GET", or as the result of viewing a resource on the local
file system). The document source generally refers to the "payload" of the user
agent's request, and does not generally include information exchanged as part
of the transfer protocol. The document source is data that is prior to any
repair by the user agent (e.g., prior to repairing invalid markup). "Text
source" refers to document source that is composed of text.
-
Documentation
- Documentation refers to information that supports the use
of a user agent. This information may be found in manuals, installation
instructions, the help system, tutorials, etc. Documentation may be distributed
(e.g., some parts may be delivered on CD-ROM, others on the Web). Refer to guideline 12 for information about
documentation requirements.
- Element, element type
- This document uses the terms "element" and "element type"
in the sense employed by the XML 1.0 specification ([XML], section 3): an element type is
a syntactic construct of a document type definition (DTD) for its application.
This sense is also relevant to structures defined by XML schemas. The document
also uses the term "element" more generally to mean a type of content (such as
video or sound) or a logical construct (such as a header or list).
-
Enabled element, disabled element
- An enabled element is a piece of content
with associated behaviors that may be activated through the user interface or
through an API. The set
of elements that a user agent enables is generally derived from, but is not
limited to, the set of interactive
elements defined by implemented markup languages.
Some elements may only be enabled elements for part of a user session. For
instance, an element may be disabled by a script as the result of user
interaction. Or, an element may only be enabled during a given time period
(e.g., during part of a SMIL 1.0 [SMIL] presentation). Or, the user
may be viewing content in "read-only" mode, which may disable some
elements.
A disabled element is a piece of content that is potentially an
enabled element, but is not in the current session. One example of a disabled
element is a menu item that is unavailable in the current session; it might be
"greyed out" to show that it is disabled. Generally, disabled elements will be
interactive elements that are not
enabled in the current session. This document distinguishes disabled elements
(not currently enabled) from non-interactive elements (never enabled).
For the requirements of this document, user
selection does not constitute user interaction with enabled elements. See
the definition of content focus.
Note: Enabled and disabled elements come from content; they
are not part of the user agent user
interface.
Note: The term "active element" is not used in this
document since it may suggest several different concepts, including:
interactive element, enabled element, an element "in the process of being
activated" (which is the meaning of ':active' in CSS2 [CSS2], for example).
-
Equivalent (for content)
- The term "equivalent" is used in this document as it is
used in the Web Content Accessibility Guidelines 1.0 [WCAG10]:
Content is "equivalent" to other content when both fulfill essentially the
same function or purpose upon presentation to the user. In the context of this
document, the equivalent must fulfill essentially the same function for the
person with a disability (at least insofar as is feasible, given the nature of
the disability and the state of technology), as the primary content does for
the person without any disability.
Equivalents include text equivalents
(e.g., text equivalents for images, text transcripts for audio tracks, or
collated text transcripts for a movie) and non-text equivalents (e.g., a
prerecorded audio description of a
visual track of a movie, or a sign language video rendition of a written
text).
Each markup language defines its own mechanisms for specifying conditional content, and these
mechanisms may be used by authors to provide text equivalents. For instance, in
HTML 4
[HTML4] or SMIL 1.0 [SMIL], authors may use the
"alt
" attribute to specify a text equivalent for some elements. In
HTML 4, authors may provide equivalents and other conditional content in
attribute values (e.g., the "summary" attribute for the TABLE
element), in element content (e.g., OBJECT
for external content it
specifies, NOFRAMES
for frame equivalents, and
NOSCRIPT
for script equivalents), and in prose. Please consult the Web
Content Accessibility Guidelines 1.0 [WCAG10] and its associated
Techniques document [WCAG10-TECHS] for more
information about equivalents.
- Events and
scripting, event handler, event type
- User agents often perform a task when an event having a
particular "event type" occurs, including user interface, changes to content,
loading of content, a request from the operating environment, etc.
Some markup languages allow authors to specify that a script, called an event
handler, be executed when an event of a given type occurs. An
event handler is
explicitly associated with an element when the event handler
is associated with that element through markup or the DOM.
The term "event bubbling"
describes a programming style where a single event handler dispatches events to
more than one element. In this case, the event handlers are not explicitly
associated with the elements receiving the events (except for the single
element that dispatches the events).
Note: The combination of HTML, style sheets, the Document
Object Model (DOM), and scripting is commonly referred to as
"Dynamic HTML" or DHTML. However, as there is no W3C specification that
formally defines DHTML, this document only refers to event handlers and
scripts.
-
Explicit user request
- In this document, the term "explicit user request" refers to any user
interaction through the user agent user
interface (not through rendered content),
the focus, or the
selection. User requests are made, for example, through user agent user interface
controls and keyboard bindings.
Some examples of explicit user requests include when the user selects "New
viewport", responds "Yes" to a prompt in the user agent's user interface,
configures the user agent to behave in a certain way, or changes the selection
or focus with the keyboard or pointing device.
Note: Users make mistakes. For example, a user may
inadvertently respond "yes" to a prompt when they meant "no." In this document,
this type of mistake is still considered an explicit user request.
- Focus, content focus, user interface
focus,
current focus
- In this document, the term "content focus" (required by checkpoint 9.1) refers to a
user agent mechanism that has all of the following properties:
- It designates zero or one element in content
that is either enabled or disabled. In general, the focus
should only designate enabled elements, but it may also designate disabled
elements.
- It has state: the user may "set it" (programmatically or through the user
interface) on an enabled element.
Events may be triggered when the focus is set (or unset). Which events are
triggered depends on the content (e.g., HTML events and CSS pseudo-classes) or
user interface settings.
- Once it has been set, it may be used to trigger other behaviors associated
with the enabled element (e.g., the user may activate a link or change the
state of a form control). These behaviors may be triggered programmatically or
through the user interface (e.g., through keyboard events).
User interface mechanisms may resemble content focus, but do not satisfy all
of the properties. For example, text editors often implement a "caret" that
indicates the current location of text input or editing. The caret may have
state and may respond to input device events, but it does not enable users to
activate the behaviors associated with enabled elements.
The user interface focus shares the properties of the content focus except
that, rather than designating pieces of content, it designates zero or one control of the user agent user interface
that has associated behaviors (e.g., radio button, text box, menu, etc.).
On the screen, the content focus may be
highlighted using colors, fonts, graphics, magnification, etc. The content
focus may also be highlighted when rendered as synthesized speech, for example
through changes in speech prosody. The
dimensions of the rendered content focus may exceed those of the
viewport.
In this document, each viewport is expected to have at most one content
focus and at most one user interface focus. This document includes requirements
for content focus only, for user interface focus only, and for both. When a
requirement refers to both, the term "focus" is used.
When several viewports coexist, at most one viewport's
content focus or user interface focus responds to input
events; this is called the current focus.
-
Graphical
- In this document, the term "graphical" refers to
information (text, colors, graphics, images, animations, etc.) rendered for
visual consumption.
- Highlight
- In this document, "to highlight" means to emphasize
through the user interface. For example, user agents highlight which content is
selected or focused. Graphical highlight mechanisms include dotted boxes,
underlining, and reverse video. Synthesized speech highlight mechanisms include
alterations of voice pitch and volume ("speech prosody").
- Image
- This document uses the term "image" to refer (as is
commonly the case) to pictorial content. However, in this
document, term image is limited to static (i.e., unmoving) visual information.
See also the definition of animation.
- Input configuration
- An input configuration is the set of "bindings" between
user agent functionalities and
user interface input mechanisms (e.g., menus, buttons, keyboard keys, voice
commands, etc.). The default input configuration is the set of bindings the
user finds after installation of the software; it must be documented (per checkpoint 12.3]). Input
configurations may be affected by author-specified bindings (e.g., through the
"accesskey" attribute of HTML 4 [HTML4]).
- Interactive element,
non-interactive element,
- An interactive element is piece of content that, by
specification, may have associated behaviors to be executed or carried out as a
result of user or programmatic interaction. For instance, the interactive
elements of HTML 4 [HTML4] include: links, image maps,
form elements, elements with a value for the "longdesc" attribute, and elements
with event handlers explicitly associated
with them (e.g., through the various "on" attributes). The role of an element
as an interactive element is subject to
applicability. A non-interactive element is an element that, by format
specification, does not have associated behaviors. The expectation of this
document is that interactive elements become enabled elements in some sessions,
and non-interactive elements never become enabled elements.
- Natural language
- Natural language is spoken, written, or signed human
language such as French, Japanese, and American Sign Language. On the Web, the
natural language of content may be specified by markup or HTTP
headers. Some examples include the
"lang" attribute in HTML 4 ([HTML4] section 8.1), the "xml:lang"
attribute in XML 1.0 ([XML], section 2.12), the
HTML 4 "hreflang" attribute for links in HTML 4
([HTML4],
section 12.1.5), the HTTP Content-Language header ([RFC2616], section 14.12) and the
Accept-Language request header ([RFC2616], section 14.4). See also
the definition of script.
-
Normative,
informative
- What is identified as "normative" is required for conformance
(noting that one may conform in a variety of well-defined ways to this
document). What is identified as "informative" (sometimes, "non-normative") is
never required for conformance.
- Operating
environment
- The term "operating environment" refers to the environment
that governs the user agent's operation, whether it is an operating system or a
programming language environment such as Java.
-
Override
- In this document, the term "override" means that one
configuration or behavior preference prevails over another. Generally, the
requirements of this document involve user preferences prevailing over author
preferences and user agent default settings and behaviors. Preferences may be
multi-valued in general (e.g., the user prefers blue over red or yellow), and
include the special case of two values (e.g., turn on or off blinking text
content).
- Placeholder
- A placeholder is content generated by the user agent to
replace author-supplied content. A placeholder may be generated as the result
of a user preference (e.g., to not render images) or as
repair content (e.g., when an image cannot be found). Placeholders can be
any type of content, including text, images, and audio cues.
This document includes requirements that the user be able to view the
original author-supplied content associated with a placeholder. To satisfy
these requirements, the user agent might render the content in place of the
placeholder or in a separate viewport (leaving the placeholder as is). A
request to view the original content associated with a
placeholder is considered an explicit user request to render
that content.
This document does not require user agents to include placeholders in the document object. A placeholder that
is inserted in the document object should conform to the Web Content
Accessibility Guidelines 1.0 [WCAG10]. If a placeholder is not
part of the document object, it is part of the user interface only (and
subject, for example, to checkpoint
1.3).
-
Plug-in
- A plug-in is a program that runs as part of the user agent
and that is not part of content. Users generally
choose to include or exclude plug-ins from their user agent.
-
Point of regard
- The point of regard is a position in rendered content that the user is
presumed to be viewing. The dimensions of the point of regard may vary. For
example, it may be a point (e.g., a moment in an audio rendering or a cursor in
a graphical rendering), or a range of text (e.g., focused text), or a
two-dimensional area (e.g., content rendered through a two-dimensional
graphical viewport). The point of regard is almost always within the viewport,
but it may exceed the spatial or temporal
dimensions of the viewport (see the definition of rendered content for more
information about viewport dimensions). The point of regard may also refer to a
particular moment in time for content that changes over time (e.g., an audio-only presentation).
User agents may determine the point of regard in a number of ways, including
based on viewport position in content,
content focus, selection, etc. A user agent should not
change the point of regard unexpectedly as this may disorient the user. The
point of regard should be available programmatically (e.g., for assistive
technologies).
-
Profile
- A profile is a named and persistent representation of user preferences that
may be used to configure a user agent. Preferences include input
configurations, style preferences, natural language preferences, etc. In operating environments with
distinct user accounts, profiles enable users to reconfigure software quickly
when they log on, and profiles may be shared by several users.
Platform-independent profiles are useful for those who use the same user agent
on different platforms.
-
Prompt
- In this document, "to prompt" means to require input from
the user. The user agent should allow users to
configure how they wish to be prompted. For instance, for a user agent
functionality X, configurations might include: always prompt me before doing X,
always do X without prompting me, never do X but tell me when you could have,
never do X and never tell me that you could have, etc.
- Properties, values, and
defaults
- A user agent renders a document by applying formatting
algorithms and style information to the document's elements. Formatting depends
on a number of factors, including where the document is rendered: on screen, on
paper, through loudspeakers, on a braille display, on a mobile device, etc.
Style information (e.g., fonts, colors, synthesized speech prosody, etc.) may
come from the elements themselves (e.g., certain font and phrase elements in
HTML), from style sheets, or from user agent settings. For the purposes of
these guidelines, each formatting or style option is governed by a property and
each property may take one value from a set of legal values. Generally in this
document, the term "property"
has the meaning defined in CSS 2 ([CSS2], section 3). A reference to
"styles" in this document means a set of style-related properties.
- The value given to a property by a user agent when it is
installed is called the property's
default value.
- Recognize
- Authors encode information in markup languages, style
sheet languages, scripting languages, protocols, etc. When the information is
encoded in a manner that allows the user agent to process it with certainty,
the user agent can "recognize" the information. For instance, HTML allows
authors to specify a heading with the H1 element, so a user agent that
implements HTML can recognize that content as a heading. If the author creates
headings using a visual effect alone (e.g., by increasing the font size), then
the author has encoded the heading in a manner that does not allow the user
agent to recognize it as a heading.
Some requirements of this document depend on content roles, content
relationships, timing relationships, and other information supplied by the
author. These requirements only apply when
the author has encoded that information in a manner that the user agent can
recognize. See the section on conformance
in User Agent Accessibility Guidelines 1.0 [UAAG10] for more information about
applicability.
In practice, user agents will rely heavily on information that the author
has encoded in a markup language or style sheet language. On the other hand,
behaviors, style, meaning encoded in a script, and
markup in an unfamiliar XML namespace may not be recognized by the user agent
as easily or at all.
-
Rendered content, rendered text
- Rendered content is the part of content
that the user agent makes available to the user's senses of sight and hearing
(and only those senses for the purposes of this document). Any content that
causes an effect that may be perceived through these senses constitutes
rendered content. This includes text characters, images, style sheets, scripts,
and anything else in content that, once processed, may be perceived through
sight and hearing.
The term "rendered text" refers to text content that is rendered in
a way that communicates information about the characters themselves, whether
visually or as synthesized speech.
- In the context of this document, invisible content is content
that influences graphical rendering of other content but is not rendered
itself. Similarly,
silent content is content that influences audio rendering of
other content but is not rendered itself. Neither invisible nor silent content
is considered rendered content.
-
Repair content, repair text
- In this document, the term "repair content" refers to
content generated by the user agent in order to correct an error condition.
"Repair text" means repair content consisting only of text. Some error
conditions that may lead to the generation of repair content include:
- Erroneous or incomplete content (e.g., ill-formed markup, invalid markup,
missing conditional content that is
required by format specification);
- Missing resources for handling or rendering content (e.g., the user agent
lacks a font family to display some characters, the user agent does not
implement a particular scripting language).
This document does not require user agents to include repair content in the
document object. Repair content
inserted in the document object should conform to the Web Content Accessibility
Guidelines 1.0
[WCAG10]. For more information about repair techniques for Web
content and software, refer to "Techniques for Authoring Tool Accessibility
Guidelines 1.0" [ATAG10-TECHS].
- Script
- In this document, the term "script" almost always refers to a scripting
(programming) language used to create dynamic Web content. However, in
checkpoints referring to the written (natural) language of content, the term
"script" is used as in Unicode [UNICODE] to mean "A collection of
symbols used to represent textual information in one or more writing systems."
Information encoded in scripts may be difficult for a user agent to recognize. For instance, a user agent is
not expected to recognize that, when executed, a script will calculate a
factorial. The user agent will be able to recognize some information in a
script by virtue of implementing the scripting language or a known program
library (e.g., the user agent is expected to recognize when a script will open
a viewport or retrieve a resource from the Web).
-
Selection, current selection
- In this document, the term "selection" refers to a user
agent mechanism for identifying a range of content
(e.g., text, images, etc.). Generally, user agents limit selection to text
content (e.g., one or more fragments of text). The
selection may be structured (based on the document tree) or unstructured
(e.g., text-based). The range may be empty.
On the screen, the selection may be
highlighted using colors, fonts, graphics, magnification, etc. The
selection may also be highlighted when rendered as synthesized speech, for
example through changes in speech prosody. The dimensions of the rendered
selection may exceed those of the viewport.
The selection may be used for a variety of purposes: for cut and paste
operations, to designate a specific element in a document for the purposes of a
query, as an indication of point of regard,
etc.
The selection has state, and the user may "set it" (programmatically or
through the user interface).
In this document, each viewport is expected to have at most one selection.
When several viewports coexist, at most one viewport's
selection responds to input events; this is called the current selection.
See the section on the
Selection label for information about implementing a selection and
conformance.
Note: Some user agents may also implement a selection for
designating a range of information in the user agent user interface.
The current document only includes requirements for a content
selection mechanism.
-
Serial access, sequential
navigation
- In this document, the expression "serial access" refers to
one-dimensional access to rendered content.
Some examples of serial access include listening to an audio stream or watching
a video (both of which involve one temporal dimension), or reading a series of
lines of braille one line at a time (one spatial dimension). Many users with
blindness have serial access to content rendered as audio, synthesized speech,
or lines of braille.
The expression "sequential navigation" refers to navigation through an
ordered set of items (e.g., the enabled elements in a document, a
sequence of lines or pages, or a sequence of menu options). Sequential
navigation implies that the user cannot skip directly from one member of the
set to another, in contrast to direct or structured navigation (see guideline 9 for information about
these types of navigation). Users with blindness or some users with a physical
disability may navigate content sequentially (e.g., by navigating through
links, one by one, in a graphical viewport with or without the aid of an
assistive technology). Sequential navigation is important to users who cannot
scan rendered content visually for context and also benefits users unfamiliar
with content. The increments of sequential navigation may be determined by a
number of factors, including element type (e.g., links only), content structure
(e.g., navigation from heading to heading), and the current navigation context
(e.g., having navigated to a table, allow navigation among the table
cells).
Users with serial access to content or who navigate sequentially may require
more time to access content than users who use direct or structured
navigation.
-
Support,
implement,
conform
- In this document, the terms "support", "implement", and
"conform" all refer to what a developer has designed a user agent to do, but
they represent different degrees of specificity. A user agent "supports"
general classes of objects, such as "images" or "Japanese". A user agent
"implements" a specification (e.g., the PNG and SVG image format
specifications, a particular scripting language, etc.), or an API (e.g.,
the DOM API) when it has been programmed to follow all or part of a
specification. A user agent "conforms to" a specification when it implements
the specification and satisfies its conformance criteria. This
document includes some conformance requirements to other specifications (e.g.,
to a particular level of the "Web Content Accessibility Guidelines 1.0"
[WCAG10]).
-
Synchronize
- In this document, "to synchronize" refers to the act of
time-coordinating two or more presentation components (e.g., in a multimedia
presentation, a visual track with captions). For Web
content developers, the requirement to synchronize means to provide the data
that will permit sensible time-coordinated rendering by a user agent. For
example, Web content developers can ensure that the segments of caption text
are neither too long nor too short, and that they map to segments of the visual
track that are appropriate in length. For user agent developers, the
requirement to synchronize means to present the content in a sensible
time-coordinated fashion under a wide range of circumstances including
technology constraints (e.g., small text-only displays), user limitations (slow
reading speeds, large font sizes, high need for review or repeat functions),
and content that is sub-optimal in terms of accessibility.
- Text
- In this document, the term "text" used by itself refers to
a sequence of characters from a markup language's document character set. Refer
to the "Character Model for the World Wide Web " [CHARMOD] for more information
about text and characters. Note: This document makes use of
other terms that include the word "text" that have highly specialized meanings:
collated text transcript, non-text content, text content, non-text element, text element, text
equivalent, and text transcript.
-
Text content, non-text content, text
element, non-text element, text equivalent, non-text
equivalent
- As used in this document a "text element" adds text characters to either content or the
user interface. Both in the Web Content Accessibility Guidelines 1.0
[WCAG10] and
in this document, text elements are presumed to produce text that can be
understood when rendered visually, as synthesized speech, or as Braille. Such
text elements benefit at least these three groups of users:
- visually-displayed text benefits users who are deaf and adept in reading
visually-displayed text;
- synthesized speech benefits users who are blind and adept in use of
synthesized speech;
- braille benefits users who are blind, and possibly deaf-blind, and adept at
reading braille.
A text element may consist of both text and non-text data. For instance, a
text element may contain markup for style (e.g., font size or color), structure
(e.g., heading levels), and other semantics. The essential function of the text
element should be retained even if style information happens to be lost in
rendering.
A user agent may have to process a text element in order to have access to
the text characters. For instance, a text element may consist of markup, it may
be encrypted or compressed, or it may include embedded text in a binary format
(e.g., JPEG).
"Text content" is content that is composed of one or more text elements. A
"text equivalent" (whether in content or the user interface) is an equivalent composed of one
or more text elements. Authors generally provide text equivalents for content
by using the conditional
content mechanisms of a specification.
A "non-text element" is an element (in content or the user interface) that
does not have the qualities of a text element. "Non-text content" is composed
of one or more non-text elements. A "non-text equivalent" (whether in content
or the user interface) is an equivalent
composed of one or more non-text elements.
-
Text decoration
- In this document, a "text decoration" is any stylistic effect that the user
agent may apply to visually rendered text that does
not affect the layout of the document (i.e., does not require reformatting when
applied or removed). Text decoration mechanisms include underline, overline,
and strike-through.
-
Text transcript
- A text transcript is a text equivalent of audio
information (e.g., an audio-only presentation or
the audio track of a movie or other
animation). It provides text for both spoken words and non-spoken sounds such
as sound effects. Text transcripts make audio information accessible to people
who have hearing disabilities and to people who cannot play the audio. Text
transcripts are usually created by hand but may be generated on the fly (e.g.,
by voice-to-text converters). See also the definitions of captions and collated text
transcripts.
- User agent
- In this document, the term "user agent" is used in two
ways:
- The software and documentation components that together, conform to the
requirements of User Agent Accessibility Guidelines 1.0 [UAAG10]. This
is the most common use of the term in this document and is the usage in the
checkpoints.
- Any software that retrieves and renders Web content for users. This may
include Web browsers, media players, plug-ins,
and other programs – including assistive technologies -- that
help in retrieving and rendering Web content.
-
User agent default styles
- User agent default styles are style property
values applied in the absence of any author or user styles. Some markup
languages specify a default rendering for documents in that markup language.
Other specifications may not specify default styles. For example,
XML 1.0
[XML] does not specify default styles for XML documents.
HTML 4
[HTML4] does not specify default styles for HTML documents, but the
CSS 2
[CSS2] specification suggests a sample default
style sheet for HTML 4 based on current practice.
-
User interface,
user interface control
- For the purposes of this document, user interface includes
both:
- the user agent user
interface, i.e., the controls (e.g., menus, buttons, prompts, and
other components for input and output) and mechanisms (e.g., selection and
focus) provided by the user agent ("out of the box") that are not created by content.
- the "content user interface", i.e., the enabled elements that are part of
content, such as form controls, links, applets,
etc.
The document distinguishes them only where required for clarity. For more
information, see the section on requirements
for content, for user agent features, or both in User Agent Accessibility
Guidelines 1.0
[UAAG10].
The term "user interface control" refers to a component of the user agent
user interface or the content user interface, distinguished where
necessary.
-
User styles
- User styles are style property
values that come from user interface settings, user style sheets, or other
user interactions.
- Views, viewports
- The user agent renders content through one or more
viewports. Viewports include windows, frames, pieces of paper, loudspeakers,
virtual magnifying glasses, etc. A viewport may contain another viewport (e.g.,
nested frames). User agent user interface
controls such as prompts, menus, alerts, etc., are not viewports.
Graphical and tactile viewports have two spatial dimensions. A
viewport may also have temporal dimensions, for instance when audio, speech,
animations, and movies are rendered. When the dimensions (spatial or temporal)
of rendered content exceed the dimensions of the viewport, the user agent
provides mechanisms such as scroll bars and advance and rewind controls so that
the user can access the rendered content "outside" the viewport. Examples
include: when the user can only view a portion of a large document through a
small graphical viewport, or when audio content has already been played.
When several viewports coexist, only one has the
current focus at a given moment. This viewport is
highlighted to make it stand out.
User agents may render the same content in a variety of ways; each rendering
is called a view. For
instance, a user agent may allow users to view an entire document or just a
list of the document's headers. These are two different views of the
document.
- Visual-only
presentation
- A visual-only presentation is content consisting
exclusively of one or more visual tracks presented
concurrently or in series. A silent movie is an example of a visual-only
presentation.
-
Visual track
- A visual object is content rendered through a graphical viewport. Visual objects include graphics,
text, and visual portions of movies and other animations. A visual track is a
visual object that is intended as a whole or partial presentation. A visual
track does not necessarily correspond to a single physical object or software
object.
-
Voice browser
- From "Introduction and Overview of W3C Speech Interface Framework"
[VOICEBROWSER]: "A voice browser is a device (hardware and software)
that interprets voice markup languages to generate voice output, interpret
voice input, and possibly accept and produce other modalities of input and
output."
- Web resource
- The term "Web resource" is used in this document in
accordance with Web Characterization Terminology and Definitions Sheet [WEBCHAR] to
mean anything that can be identified by a Uniform Resource Identifier
(URI); refer to RFC 2396 [RFC2396].
For the latest version of any W3C specification please
consult the list of W3C Technical Reports at
http://www.w3.org/TR/. Some documents listed below may have been superseded
since the publication of this document.
Note: In this document, bracketed labels such as "[HTML4]"
link to the corresponding entries in this section. These labels are also
identified as references through markup.
There are two recommended ways to refer to the "Techniques for User Agent
Accessibility Guidelines 1.0" (and to W3C documents in general):
- References to a specific version of "Techniques for User Agent
Accessibility Guidelines 1.0". For example, use the "this version"
URI to refer to the current document:
http://www.w3.org/TR/2002/WD-UAAG10-TECHS-20020821/.
- References to the latest version of "Techniques for User Agent
Accessibility Guidelines 1.0". Use the "latest version" URI to refer to the
most recently published document in the series:
http://www.w3.org/TR/UAAG10-TECHS/.
In almost all cases, references (either by name or by link) should be to a
specific version of the document. W3C will make every effort to make this
document indefinitely available at its original address in its original form.
The top of this document includes the relevant catalog metadata for specific
references (including title, publication date, "this version"
URI, editors' names, and copyright information).
An XHTML 1.0
[XHTML10] paragraph including a reference to this specific document
might be written:
<p>
<cite><a href="http://www.w3.org/TR/2002/WD-UAAG10-TECHS-20020821/">
"Techniques for User Agent Accessibility Guidelines 1.0"</a></cite>,
I. Jacobs, J. Gunderson, E. Hansen, eds.,
W3C Working Draft, 21 August 2002.
The <a href="http://www.w3.org/TR/UAAG10-TECHS/">latest
version</a> of this document is available at
http://www.w3.org/TR/UAAG10-TECHS/.</p>
For very general references to this document (where stability of content,
anchors, etc., is not required), it may be appropriate to refer to the latest
version of this document. In this case, please use the "latest version" URI at
the top of this document.
- [CSS1]
- "Cascading
Style Sheets (CSS1) Level 1 Specification", B. Bos, H. Wium Lie,
eds., 17 December 1996, revised 11 January 1999. This W3C Recommendation is
http://www.w3.org/TR/1999/REC-CSS1-19990111.
- [CSS2]
- "Cascading
Style Sheets, level 2 (CSS2) Specification", B. Bos, H. Wium Lie, C.
Lilley, and I. Jacobs, eds., 12 May 1998. This W3C Recommendation is
http://www.w3.org/TR/1998/REC-CSS2-19980512/.
- [DOM2CORE]
-
"Document Object Model (DOM) Level 2 Core Specification", A. Le
Hors, P. Le Hégaret, L. Wood, G. Nicol, J. Robie, M. Champion, S. Byrne,
eds., 13 November 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Core-20001113/.
- [DOM2STYLE]
-
"Document Object Model (DOM) Level 2 Style Specification", V.
Apparao, P. Le Hégaret, C. Wilson, eds., 13 November 2000. This W3C
Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/.
- [ECMASCRIPT]
- "ECMAScript
Language Specification", European Computer Manufacturers
Association, December 1999. This specification is available at
http://www.ecma.ch/ecma1/STAND/ECMA-262.HTM.
- [INFOSET]
- "XML
Information Set", J. Cowan and R. Tobin, eds., 24 October 2001. This
W3C Recommendation is http://www.w3.org/TR/2001/REC-xml-infoset-20011024/.
- [JAVA]
- "The Java Language
Specification", Sun Microsystems Inc., J. Gosling, B. Joy, and G.
Steele, September 1996. The specification is available at
http://java.sun.com/docs/books/jls.
- [RFC2046]
- "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types", N. Freed, N.
Borenstein, November 1996.
- [UAAG10]
- "User Agent Accessibility
Guidelines 1.0", I. Jacobs, J. Gunderson, E. Hansen, eds. The latest
draft of the guidelines is available at http://www.w3.org/TR/UAAG10/.
- [WCAG10]
- "Web
Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden,
and I. Jacobs, eds., 5 May 1999. This W3C Recommendation is
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/.
Some of the references in this section become normative if they are used to
satisfy the requirements of
guideline 6 and
guideline 8.
- [AT1998]
- The Assistive
Technology Act of 1998, 13 November 1998, United States P.L.
105-394.
- [ATAG10]
- "Authoring
Tool Accessibility Guidelines 1.0", J. Treviranus, C.
McCathieNevile, I. Jacobs, and J. Richards, eds., 3 February 2000. This W3C
Recommendation is http://www.w3.org/TR/2000/REC-ATAG10-20000203/.
-
[ATAG10-TECHS]
-
"Techniques for Authoring Tool Accessibility Guidelines 1.0", J.
Treviranus, C. McCathieNevile, I. Jacobs, and J. Richards, eds., 4 May 2000.
This W3C Note is http://www.w3.org/TR/2000/NOTE-ATAG10-TECHS-20000504/.
- [CHARMOD]
- "Character
Model for the World Wide Web", M. Dürst and F. Yergeau, eds.,
30 April 2002. This W3C Working Draft is
http://www.w3.org/TR/2002/WD-charmod-20020430/. The latest version is available at
http://www.w3.org/TR/charmod/.
- [CSS-ACCESS]
-
"Accessibility Features of CSS", I. Jacobs, J. Brewer, 4 August
1999. This W3C Note is http://www.w3.org/1999/08/NOTE-CSS-access-19990804.
- [DOM2EVENTS]
-
Document Object Model (DOM) Level 2 Events Specification, T. Pixley,
ed., 13 November 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/.
- [DOM2RANGE]
-
Document Object Model (DOM) Level 2 Traversal and Range
Specification, J. Kesselman, J. Robie, M. Champion, P. Sharpe, V.
Apparao, and L. Wood, eds., 13 November 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Traversal-Range-20001113/.
- [DOM3EVENTS]
-
Document Object Model (DOM) Level 3 Events Specification, T. Pixley,
ed., 8 February 2002. This W3C Working Draft is
http://www.w3.org/TR/2002/WD-DOM-Level-3-Events-20020208/. The latest version is available
at http://www.w3.org/TR/DOM-Level-3-Events/.
- [HTML4]
- "HTML 4.01
Recommendation", D. Raggett, A. Le Hors, and I. Jacobs, eds., 24
December 1999. This W3C Recommendation is
http://www.w3.org/TR/1999/REC-html401-19991224/.
- [MATHML20]
-
"Mathematical Markup Language (MathML) Version 2.0", D. Carlisle, P.
Ion, R. Miner, N. Poppelier, et al., 21 February 2001. This W3C Recommendation
is http://www.w3.org/TR/2001/REC-MathML2-20010221/.
- [PNG]
- "PNG
(Portable Network Graphics) Specification 1.0", T. Boutell, ed., 1
October 1996. This W3C Recommendation is http://www.w3.org/TR/REC-png.
-
[PWD-USE-WEB]
- The "How
People with Disabilities Use the Web", J. Brewer. This document
provides an introduction to use of the Web by people with disabilities. It is
not yet a formal W3C Working Draft.
- [RFC2396]
- "Uniform Resource
Identifiers (URI): Generic Syntax", T. Berners-Lee, R. Fielding, L.
Masinter, August 1998.
- [RFC2616]
- "Hypertext Transfer
Protocol – HTTP/1.1", J. Gettys, J. Mogul, H. Frystyk, L.
Masinter, P. Leach, T. Berners-Lee, June 1999.
- [SMIL]
- "Synchronized
Multimedia Integration Language (SMIL) 1.0 Specification", P.
Hoschka, ed., 15 June 1998. This W3C Recommendation is
http://www.w3.org/TR/1998/REC-smil-19980615/.
-
[SMIL-ACCESS]
-
"Accessibility Features of SMIL", M-R. Koivunen, I. Jacobs, 21
September 1999. This W3C Note is
http://www.w3.org/TR/1999/NOTE-SMIL-access-19990921/.
- [SMIL20]
- Synchronized
Multimedia Integration Language (SMIL 2.0) Specification, J. Ayars,
et al., eds., 7 August 2001. This W3C Recommendation is
http://www.w3.org/TR/2001/REC-smil20-20010807/.
- [SVG]
- "Scalable Vector
Graphics (SVG) 1.0 Specification", J. Ferraiolo, ed., 2 August 2000.
This W3C Candidate Recommendation is
http://www.w3.org/TR/2000/CR-SVG-20000802/.
- [SVG-ACCESS]
-
"Accessibility Features of SVG", C. McCathieNevile and M.-R.
Koivunen, 7 August 2000. This W3C Note is
http://www.w3.org/TR/2000/NOTE-SVG-access-20000807/.
- [UNICODE]
- "The Unicode
Standard, Version 3.2". This technical report of the Unicode Consortium is available at
http://www.unicode.org/unicode/reports/tr28/. This is a revision of "The
Unicode Standard, Version 3.0", The Unicode Consortium, Addison-Wesley
Developers Press, 2000. ISBN 0-201-61633-5. Refer also to
http://www.unicode.org/unicode/standard/versions/. For information about character encodings, refer to Unicode Technical Report
#17 "Character Encoding Model".
-
[VOICEBROWSER]
-
"Introduction and Overview of W3C Speech Interface Framework", J.
Larson, 4 December 2000. This W3C Working Draft is
http://www.w3.org/TR/2000/WD-voice-intro-20001204/. The latest version is available at
http://www.w3.org/TR/voice-intro/. This document includes references to
additional W3C specifications about voice browser technology.
-
[WCAG10-TECHS]
- "Techniques for Web
Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden,
and I. Jacobs, eds., 6 November 2000. This W3C Note is
http://www.w3.org/TR/1999/WAI-WEBCONTENT-TECHS-19990505/. The latest version is available at
http://www.w3.org/TR/WCAG10-TECHS/. Additional format-specific techniques
documents are available from this Note.
- [WEBCHAR]
- "Web
Characterization Terminology and Definitions Sheet", B. Lavoie, H.
F. Nielsen, eds., 24 May 1999. This is a W3C Working Draft that defines some
terms to establish a common understanding about key Web concepts. This W3C
Working Draft is http://www.w3.org/1999/05/WCA-terms/01.
- [XFORMS10]
- "XForms
1.0", M. Dubinko, J. Dietl, R. Merrick, T.V. Raman, 18 January 2002.
This W3C Working Draft is http://www.w3.org/TR/2002/WD-xforms-20020118/. The latest version of XForms 1.0 is
available at http://www.w3.org/TR/xforms/.
- [XHTML10]
- "XHTML[tm]
1.0: The Extensible HyperText Markup Language", S. Pemberton, et
al., 26 January 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-xhtml1-20000126/.
- [XLINK]
- "XML Linking
Language (XLink) Version 1.0", S. DeRose, E. Maler, D. Orchard, B.
Trafford, eds., 3 July 2000. This XML 1.0 Candidate Recommendation is
http://www.w3.org/TR/2000/CR-xlink-20000703/.
- [XML]
- "Extensible
Markup Language (XML) 1.0", T. Bray, J. Paoli, C.M.
Sperberg-McQueen, eds., 10 February 1998. This W3C Recommendation is
http://www.w3.org/TR/1998/REC-xml-19980210.
- [XMLSTYLE]
-
"Associating Style Sheets with XML documents Version 1.0", J. Clark,
ed., 29 June 1999. This W3C Recommendation is
http://www.w3.org/1999/06/REC-xml-stylesheet-19990629/
- [XSLT]
- "XSL
Transformations (XSLT) Version 1.0", J. Clark, 16 November 1999.
This W3C Recommendation is http://www.w3.org/TR/1999/REC-xslt-19991116.
Note: W3C does not guarantee the stability of any of
the following references outside of its control. These references are included
for convenience. References to products are not endorsements of those products
by W3C.
-
[ACCESSIBILITY-DEV-HOWTO]
- "How to
Develop Accessible Linux Applications", S. Snider, ed.
-
[ACCESSIBILITY-HOWTO]
-
"Linux Accessibility HOWTO", M. de la Rue, S. Snider, eds.
- [APPLE-HI]
- Refer to the following guidelines from Apple:
- [ATK]
- The ATK
library provides a set of interfaces for accessibility in the GNOME
environment.
- [BHO]
- Browser
Helper Objects: The Browser the Way You Want It, D. Esposito,
January 1999. Refer also to
http://support.microsoft.com/support/kb/articles/Q179/2/30.asp.
- [ED-DEPT]
-
"Requirements for Accessible Software Design", US Department of
Education, version 1.1 March 6, 1997.
- [EITAAC]
-
"EITAAC Desktop Software standards", Electronic Information
Technology Access Advisory (EITAAC) Committee.
- [GECKO-API]
- The Mozilla developers offer a FAQ that explains how to
communicate with Gecko, the rendering engine in the Windows platform.
-
[GNOME-ACCESS]
- The GNOME
Accessibility Project. See in particular [Draft] How
to make GNOME 2.0 Applications Accessible.
- [IBM-ACCESS]
- "Software
Accessibility", IBM Special Needs Systems.. Refer to the IBM guidelines for
software accessibility, IBM guidelines for Java
accessibility.
- [ICCCM]
- "The Inter-Client
communication conventions manual". A protocol for communication
between clients in the X Window system.
- [ICE-RAP]
- "An
ICE Rendezvous Mechanism for X Window System Clients", W. Walker. A
description of how to use the ICE and RAP protocols for X Window clients.
-
[JAVA-ACCESS]
- "IBM Guidelines for
Writing Accessible Applications Using 100% Pure Java", R.
Schwerdtfeger, IBM Special Needs Systems.
-
[JAVA-CHECKLIST]
- "Java
Accessibility Guidelines and Checklist". IBM Special Needs
Systems.
- [JAVA-TUT]
- "The Java
Tutorial. Trail: Creating a GUI with JFC/Swing". An online tutorial
that describes how to use the Swing Java Foundation Class to build an
accessible user interface. Refer also to information on the Java Foundation Classes.
- [JAVA13]
- Refer to information about
character encodings required by Java version 1.3.
- [JAVAAPI]
- Information on Java Accessibility API can be found at Java
Accessibility Utilities.
- [MAC-ACCESS]
- Accessibility
features of the MacIntosh
- [MOTIF]
- The OSF/Motif
Style Guide.
- [MS-ENABLE]
-
Software accessibility guidelines for Windows applications. Refer also to
Built-in
accessibility features.
-
[MS-KEYBOARD]
- Information on keyboard
assistance for Internet Explorer and MS Windows.
-
[MS-SOFTWARE]
- "The
Microsoft Windows Guidelines for Accessible Software Design".
Note: This page summarizes the guidelines and includes links
to the full guidelines in various formats (including plain text).
- [MSAA]
- Information on active accessibility can be found at the Microsoft Active
Accessibility home page. See also
About Active Accessibility Support for information about Active
Accessibility SDK support provided by the MSHTML component of Internet Explorer
(for HTML documents).
-
[NOTES-ACCESS]
- "Lotus Notes
Accessibility" IBM Special Needs Systems.
- [PHOTO-RDF]
-
"Describing and retrieving photos using RDF and HTTP", Y. Lafon and
B. Bos. The 3 May 2000 version of the W3C Note is
http://www.w3.org/TR/2000/NOTE-photo-rdf-20000503/.
- [SAMI]
- Information on
Synchronized Accessible Multimedia Interchange (SAMI)
accessibility.
- [SUN-DESIGN]
- Articles, Talks, and
Papers from Sun Microsystems about accessibility.
- [SUN-HCI]
-
"Towards Accessible Human-Computer Interaction", Eric Bergman, Earl
Johnson, Sun Microsytems 1995. A substantial paper, with a valuable print
bibliography.
-
[TALKINGBOOKS]
- (USA) National Information Standards
Organization. One activity pursued by this organization concerns Digital Talking Books. Refer to the
"Digital Talking Book
Features List" and "Digital Talking Book
Standards Committee Document Navigation Features List" drafts for
more information.
- [TRACE-EZ]
- "EZ ACCESS(tm) for
electronic devices V 2.0 implementation guide", C. M. Law, G. C.
Vanderheiden, 23 February 2000. This guide, developed by the Trace Research and Development Center,
describes a simple set of interface enhancements that can be applied to
electronic devices so that they can be used by people with disabilities, or
anyone who experiences difficulty using a device in the standard method of
operation.
- [TRACE-REF]
- "Application
Software Design Guidelines" compiled by G. Vanderheiden. A thorough
reference work.
- [WHAT-IS]
- "What is Accessible Software", James W. Thatcher, Ph.D., IBM,
1997. This paper, available at the IBM
Accessibility Center, gives a short example-based introduction to the
difference between software that is accessible, and software that can be used
by some assistive technologies.
-
[XGUIDELINES]
- Information on accessibility
guidelines for Unix and X Window applications. The Open Group has various guides that
explain the Motif and Common Desktop Environment (CDE) with
topics like how users interact with Motif/CDE applications and how to customize
these environments. Note: In X, the terms client and server
are used differently from their use when discussing the Web.
A list of alternative
Web browsers (assistive technologies and other user agents designed for
accessibility) is maintained at the WAI Web site.
- [ADOBE]
- access.adobe.com. Tools
and information about Adobe PDF and accessibility. In particular, see the how to
access PDF documents through MSAA; this is a PDF document.
- [ALTIFIER]
- The Altifier Tool
generates "alt" text intelligently.
- [AMAYA]
- Amaya is W3C's test-bed browser and
editor.
- [AWB]
- The Accessible Web Browser, senior project at the University of Illinois Champaign-Urbana
-
[CSSVALIDATOR]
- W3C's CSS Validator
service.
- [DIRECTDOM]
- DirectDom technology, available from alphaWorks, allows a Java developer
to manipulate the live Document Object Model of a browser or Scalable Vector
Graphics plug-in to build rich graphical user interfaces.
- [G2]
- The G2 player version 7 for Windows.
- [HELPDB]
- HelpDB is a test tool
for Web table navigation.
- [HPR]
- Home Page Reader.
- [IE-WIN]
- Internet Explorer 5.0 for
Windows 95, Windows 98, and Windows NT. Refer also to information on using COM with
IE. Refer also to
information about monitoring HTML events in the IE document
object model.
- [JFW]
- JAWS for Windows.
- [LYNX]
- The Lynx Browser.
- [MOZILLA]
- The Mozilla browser.
- [NAVIGATOR]
- Netscape
Navigator.
- [ODP-DOM]
- Open
Directory Project information on the W3C DOM.
- [OPERA]
- The Opera Browser.
- [QUICKTIME]
- The QuickTime player.
- [TABLENAV]
- A
table navigation script from the Trace Research Center.
- [VALIDATOR]
- W3C's HTML/XML Validator
service.
- [VIAVOICE]
- ViaVoice voice
recognition software.
- [WINDOWEYES]
- Window-Eyes.
- [WINVISION]
- Winvision.
-
[BRAILLEFORMATS]
- "Braille Formats: Principles of
Print to Braille Transcription 1997" .
- [NBA]
- The (USA) National Braille
Association.
- [NBP]
- The (USA) National Braille Press.
- [RFBD]
- Recording for the Blind and
Dyslexic.
- [SAPI]
- Microsoft's Speech Application
Programming Interface.
-
[SPEAK2WRITE]
- Speak to Write is a site about
using voice recognition to promote accessibility.
- [ISO639]
- "Codes for the representation of names of languages", ISO 639:1988. For
more information, consult
http://www.iso.ch/cate/d4766.html. Refer also to
http://www.oasis-open.org/cover/iso639a.html.
The active participants of the User Agent Accessibility Guidelines Working
Group who authored this document were: James Allan (Texas School for the Blind
and Visually Impaired), Denis Anson (College Misericordia), Harvey Bingham, Jon
Gunderson (Chair of the Working Group, University of Illinois,
Urbana-Champaign), Eric Hansen (Educational Testing Service), Ian Jacobs (Team
Contact, W3C), Tim Lacy (Microsoft), David Poehlman, and Rich Schwerdtfeger
(IBM).
Many thanks to the following people who have contributed through review and
past participation in the Working Group: Paul Adelson, Jonny Axelsson, Kitch
Barnicle, Olivier Borius, Judy Brewer, Dick Brown, Bryan Campbell, Kevin Carey,
Tantek Çelik, Wendy Chisholm, David Clark, Chetz Colwell, Wilson Craig,
Nir Dagan, Daniel Dardailler, B. K. Delong, Neal Ewers, Geoff Freed, John
Gardner, Al Gilman, Larry Goldberg, Glen Gordon, John Grotting, Markku
Hakkinen, Earle Harrison, Chris Hasser, Kathy Hewitt, Philipp Hoschka, Masayasu
Ishikawa, Phill Jenkins, Earl Johnson, Jan Kärrman (for help with html2ps), Leonard Kasday,
George Kerscher, Marja-Riitta Koivunen, Peter Korn, Josh Krieger, Catherine
Laws, Aaron Leventhal, Greg Lowney, Susan Lesch, Scott Luebking, William
Loughborough, Napoleon Maou, Matt May, Charles McCathieNevile (W3C), Peter
Meijer, Karen Moses, Dirk Mueller, Masafumi Nakane, Mark Novak, Charles
Oppermann, Mike Paciello, David Pawson, Michael Pederson, Helen Petrie, Michael
Pieper, Richard Premack, Mickey Quenzer, Jan Richards, Hans Riesebos, Joe
Roeder, Lakespur L. Roca, Gregory Rosmaita, Madeleine Rothberg, Lloyd Rutledge,
Liam Quinn, T.V. Raman, Robert Savellis, Constantine Stephanidis, Jim Thatcher,
Jutta Treviranus, Claus Thogersen, Steve Tyler, Gregg Vanderheiden, Jaap van
Lelieveld, Jon S. von Tetzchner, Willie Walker, Ben Weiss, Evan Wies, Chris
Wilson, Henk Wittingen, and Tom Wlodkowski.