This section is informative.
A user agent is any software that retrieves and presents Web content for
end users. Examples include Web browsers, media players, plug-ins, and other
programs including assistive technologies, that help in retrieving, rendering
and interacting with Web content. This document specifies requirements that,
if satisfied by user agent developers, will lower barriers
to accessibility.
Overview
Accessibility involves a wide range of disabilities, including visual,
auditory, physical, speech, cognitive, language, learning, neurological
disabilities, and disabilities related to ageing. This document emphasizes
the goal of ensuring that users, including users with disabilities, have
control over their environment for accessing the Web. Key methods for
achieving that goal include:
- optional self-pacing
- configurability
- device-independence
- interoperability
- direct support for both graphical and auditory output
- adherence to published conventions.
Some users may have more than one disability, and the needs of different
disabilities may contradict. Thus, many of the requirements in this document
involve configuration as one way to ensure that a functionality designed to
improve accessibility for one user does not interfere with accessibility for
another. A default user agent setting may be useful for one user but
interfere with accessibility for another, therefore this document prefers
configuration requirements rather than requirements for default settings. For
some content, a feature required by this document may be ineffective or cause
content to be less accessible, making it imperative that the user be able to
turn off the feature. To avoid overwhelming users with an abundance of
configuration options, this document includes requirements that promote ease
of configuration and documentation of accessibility features.
This document also acknowledges the importance of author preferences,
however, requirements are included to override certain author preferences
when the user would not otherwise be able to access that content.
Some of the requirements of this document may have security implications,
such as communication through APIs, and allowing programmatic read and write
access to content and user interface
control. This document assumes that features required by this document
will be built on top of an underlying security architecture. Consequently,
unless permitted explicitly in a success criterion, this document grants no
conformance exemptions based on security issues.
The UAWG expects that software which satisfies the requirements of this
document will be more flexible, manageable, extensible, and beneficial to all
users.
UAAG 2.0 Layers of Guidance
In order to meet the varying needs of the different audiences using UAAG,
several layers of guidance are provided including overall
principles, general guidelines, testable success
criteria, and a rich collection of sufficient techniques and
resource links.
Principles - At the top are five principles that
provide the foundation for accessible user agents. Three of the
principles are congruent to Web Content Accessibility Guidelines (WCAG)
2.0: perceivable, operable, understandable. Two principles have
been added which are specific to user agents: follows
specifications and programmatic access.
Guidelines - Under the principles are guidelines.
The guidelines provide the basic goals that authors should work toward in
order to make user agents more accessible to users with different
disabilities. The guidelines are not testable, but provide the framework
and overall objectives to help authors understand the success criteria
and better implement the techniques.
Success Criteria - For each guideline, testable
success criteria are provided to allow UAAG 2.0 to be used where
requirements and conformance testing are necessary such as in design
specification, purchasing, regulation, and contractual agreements. In
order to meet the needs of different groups and different situations,
three levels of conformance are defined: A (lowest), AA, and AAA
(highest). Additional information on UAAG levels can be found in the
section on Conformance.
All of these layers of guidance (principles, guidelines, and success criteria) work together to provide guidance on
how to make user agents more accessible. Developers are encouraged to view
and apply all layers that they are able to, including the advisory
techniques, in order to best address the needs of the widest possible range
of users.
Note that even user agents that conform at the highest level (AAA) will
not be accessible to individuals with all types, degrees, or combinations of
disability, particularly in the cognitive, language, and learning areas.
Developers are encouraged to consider the full range of techniques, including
the advisory techniques, as well as to seek relevant advice about current
best practice to ensure that their user agent is accessible, as far as
possible, to this community.
UAAG 2.0 Supporting Documents
A separate document, entitled "Implementing User Agent
Accessibility Guidelines 2.0" (the "Implementing document" from here on) provides suggestions and
examples of how each success criteria might be satisfied. It also includes
references to other accessibility resources (such as platform-specific
software accessibility guidelines) that provide additional information on how
a user agent may satisfy each success criteria. The techniques in the
Implementing document are informative examples only,
and other strategies may be used or required to satisfy the success criteria.
The UAWG expects to update the Implementing document more
frequently than the current guidelines. Developers, W3C Working Groups,
users, and others are encouraged to contribute examples and resources.
Components of Web
Accessibility
Web accessibility depends not only on accessible user agents, but also on
the availability of accessible content, a factor that is greatly influenced
by the accessibility of authoring tools. For an overview of how these
components of Web development and interaction work together, see:
Levels of
Conformance
User Agents may claim conformance to UAAG 2.0 at one of three conformance
levels. The level achieved depends on the level of the success criteria that
have been satisfied. The conformance levels are:
- UAAG 2.0 Conformance at Level "A"
The user agent satisfies all of the Level A success
criteria.
- UAAG 2.0 Conformance at Level "Double-A"
The user agent satisfies all of the Level A and Level AA success
criteria.
- UAAG 2.0 Conformance at Level "Triple-A"
The user agent satisfies all of the success criteria.
2.1.1 Platform Accessibility Architecture: Support an platform accessibility architecture
relevant to the operating environment. (Level A)
2.1.2 Name, Role, State, Value,
Description: 2.1.2 Name, Role, State, Value, Description: For all user interface components including the user interface, rendered content, and alternative content, make available the name, role, state, value,
and description via an platform accessibility architecture. (Level A)
2.1.3 Accessible
Alternative: If a feature is not supported by the accessibility
architecture(s), provide an equivalent feature that does support the
accessibility architecture(s). Document the equivalent feature in the
conformance claim. (Level A)
2.1.4 Programmatic Availability of
DOMs: If the user agent implements one or more DOMs, they must be
made programmatically available to assistive technologies. (Level A)
2.1.5 Write Access: If the
user can modify the state or value of a piece of content through the user interface (e.g., by checking a
box or editing a text area), the same degree of write access is available
programmatically. (Level A)
2.1.6 Properties: If any of
the following properties are supported by the accessibility platform
architecture, make the properties available to the accessibility platform
architecture: (Level A)
- (a) the bounding dimensions and coordinates of rendered graphical
objects
- (b) font family of text
- (c) font size of text
- (d) foreground color of text
- (e) background color of text.
- (f) change state/value notifications
2.1.7 Timely Communication:
For APIs (for non-web-based user agents) implemented to satisfy the requirements of this document, ensure
that programmatic exchanges proceed at a rate such that users do not perceive
a delay. (Level A).
PRINCIPLE 3: Perceivable - The user interface
and rendered content must be presented to users in ways they can perceive
Guideline 3.1 Provide access to
alternative content.
3.1.1 Identify Presence of Alternative Content The user has the ability to have indicators rendered along with rendered elements that have alternative content (e.g. visual icons rendered in proximity of content which has short text alternatives, long descriptions, or captions). In cases where the alternative content has different dimensions than the original content, the user has the option to specify how the layout/reflow of the document should be handled. (Level A).
3.1.2 Configurable Default
Rendering: The user has a global option to specify which types of alternative content by default and, in cases where the alternative content has different dimensions than the original content, how the layout/reflow of the document should be handled. (Level A)
3.1.3 Browse and Render:
The user can browse the alternatives, switch between them, and render them according to the following (Level A):
- synchronized alternatives for time-based media (e.g., captions, audio descriptions, sign language) can be rendered at the same time as their associated audio tracks and visual tracks, and
- non-synchronized alternatives (e.g., short text alternatives, long descriptions) can be rendered as replacements for the original rendered content.
3.1.4 Rendering Alternative
(Enhanced): Provide the user with the global option to configure a
cascade of types of alternatives to render by default, in case a preferred
type is unavailable. If the alternative content has a different height or
width, then the user agent will reflow the viewport. (Level AA)
Guideline 3.3 Provide access to relationship
information.
3.3.1 Access Relationships:
Provide access to explicitly-defined relationships based on the
user's position in content (e.g., show form control's label, show label's
form control, show a cell's table headers, etc.). (Level A)
3.3.2 Location in
Hierarchy: For content in a hierarchy (e.g., tree node, nested
frame), the user can view the path of nodes leading from the root to the
content. (Level AA)
Editors' Note: Success Criteria from 3.3 have been
moved to 4.9
3.3.3 Retrieval Progress:
Show the progress of content retrieval. (Level A)
3.4.2 Repair Empty
Alternatives: The user has the option
of receiving generated repair text when the user agent recognizes that the
author has provided empty alternative content for an enabled element. (Level AA)
Guideline 3.5 Provide highlighting for
selection, content focus, enabled elements, visited links.
3.5.1 Highlighted items:
The user has the option to highlight the
following classes of information (Level A):
- (a) selection,
- (b) content focus,
- (c) recognized
enabled elements, and
- (d) recently visited links.
3.5.2 Highlighting options:
The highlighting options (with the same configurable range as the operating environment's
conventional selection utilities) include at least (Level A):
- (a) foreground colors,
- (b) background colors, and
- (c) borders (with configurable color
and width).
Guideline
3.6 Provide text configuration.
3.6.1 Configure Text: The
user can globally set the following
characteristics of visually rendered text content, overriding any specified by the author or user agent defaults (Level A):
- (a) text scale (i.e., the general size
of text) ,
- (b) font family, and
- (c) text color (i.e., foreground and
background).
3.6.2 Preserve
Distinctions: When rendered text is rescaled, distinctions
in the size of rendered text are preserved (e.g., headers continue to be
larger than body text). (Level A)
3.6.3 Option Range: The
range of options for each text characteristic includes at least (Level A):
- (a) the range offered by global preference settings supported by the operating environment (i.e configured though the Control Panel or System) utility,
or
- (b) if no such utility is available,
the range supported by the conventional APIs of
the operating environment for drawing text.
Guideline 3.7 Provide volume configuration.
3.7.1 Global Volume:
The user can globally set volume of all audio tracks it renders (including a "mute" setting) through available operating environment mechanisms. (Level A)
3.7.2 Speech Volume: The user agent allows the user to adjust the volume of all audio tracks it renders, independent or relative to the volume level at the operating environment.
Guideline 3.8 Provide synthesized speech
configuration.
3.8.1 Speech Rate and Volume: The user can set both of the following synthesized speech
characteristics, overriding any values specified by the author (Level A):
- (a) speech rate and
- (b) speech volume (independently of
other sources of audio).
3.8.2 Speech Pitch and Range: The user can set all of the following synthesized
speech characteristics, overriding any values specified by the
author (Level AA):
- (a) pitch ("pitch" refers to the
average frequency of the speaking voice), and
- (b) pitch range ("pitch range"
specifies a variation in average frequency),
3.8.3 Advanced Speech Characteristics: The
user can set all of the speech characteristics offered by the speech
synthesizer, according to the full range of values available, overriding any values specified by the
author. (Level AAA)
3.8.4 Speech Features: The
following speech features are provided (Level AA):
- (a) user-defined extensions to the
synthesized speech dictionary,
- (b) "spell-out", where text is spelled
one character at a time, or according to language-dependent pronunciation
rules,
- (c) at least two ways of speaking numerals:
one where numerals are spoken as individual digits and punctuation (e.g. 'one two zero three point five'
for 1203.5 or 'one comma two zero three point five' for 1,203.5), and
and one where full number are spoken (e.g. 'one thousand, two hundred
and three point five')".
- (d) at least two ways of speaking
punctuation: one where punctuation is spoken literally, and one
where punctuation is rendered as natural pauses.
Guideline 3.9 Provide style sheets
configuration.
Guideline 3.10 Help user to use and orient within
viewports.
3.10.1 Highlight Viewport:
The viewport with the current focus
is highlighted (including any frame that takes
current focus) using a highlight mechanism that does not rely on rendered text foreground and background
colors alone (e.g., a thick outline). (Level A)
3.10.2 Move Viewport to Selection:
When a viewport's selection changes, the viewport moves as
necessary to ensure that the new selection is at least partially in the viewport. (Level A)
3.10.3 Move Viewport to Focus:
When a viewport's content focus changes, the viewport
moves as necessary to ensure that the new content focus is at least partially
in the viewport. (Level A)
3.10.4 Resizable: The user has the option to make graphical viewports
resizable, within the limits of the display, overriding any values
specified by the author. (Level A)
3.10.5 Scrollbars:
Graphical viewports include scrollbars if the rendered content
(including after user preferences have been applied) extends beyond the
viewport dimensions, overriding any values specified by the
author. (Level A)
3.10.6 Viewport History: If
the user agent maintains a viewport history mechanism (e.g., via the "back
button") that stores previous "viable" states (i.e., that have not been
negated by the content, user agent settings or user agent extensions), it
maintains information about the point of
regard and it restores the saved values when the user returns to a state
in the history. (Level A)
3.10.7 Open on Request: The user has the option of having "top-level"viewports (e.g., windows) only open on explicit user request. In this
mode, instead of opening a viewport automatically, notify 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). (Level AA)
3.10.8 Do Not Take Focus:
When configured to allow "top-level" viewports to open without
explicit user request, the user has the option that if a "top-level"
viewport opens, neither its content focus nor its user interface focus
automatically becomes the current focus. (Level AA)
3.10.9 Stay on Top: The user has the option of having the viewport with the
current focus remain "on top" of all other viewports with which it overlaps.
(Level AA)
3.10.10 Close Viewport: The
user can close any "top-level" viewport. (Level AA)
3.10.11 Same UI: The user has the option of having all "top-level"
viewports follow the same user interface configuration as the current or
spawning viewpor. (Level AA)
3.10.12 Indicate Viewport Position:
Indicate the viewport's position relative to rendered
content (e.g., the proportion along an audio or video timeline, the
proportion of a Web page before the current position ). (Level AAA)
Guideline 3.11 Provide an effective focus
mechanism.
3.11.1 Content Focus: At
least one content focus is provided for each viewport (including frames), where enabled elements are part of the rendered content. (Level A)
3.11.2 Current Focus: The
user can make the content focus of each viewport the current
focus. (Level A)
3.11.3 User Interface Focus:
A user interface focus is
provided. (Level A)
3.11.4 Extensions Focusable:
The user interface focus can navigate within extensions to the user
interface. (Level A)
3.11.5 Hand-Off Focus: The
user agent programmatically notifies any nested user agent(s) (e.g.,
plug-ins) when focus moves to them. (Level A)
3.11.6 Retrieve Focus: At
any time, the user agent is able to retrieve focus from a nested viewport
(including nested viewports that are user agents). (Level A)
3.11.7 Return Focus:
Embedded user agents are responsible for notifying embedding user
agent that focus should move back to it. (Level A)
3.11.8 Bi-Directional: The
user can move the content focus forward or backward to
any enabled element in the viewport. (Level A)
3.11.9 Sequential Navigation:
If the author has not specified a navigation order, the default is
sequential navigation, in
document order. (Level A)
3.11.10 Only on User
Request: The user has the option of having the content focus of
a viewport only change on explicit user request. (Level
A)
3.11.11 On Focus: The user has the option
of ensuring that moving the content focus to or from an enabled element does not cause the
user agent to take any further action. (Level A)
3.12.1 Text View: For content authored in text formats, a view of the text source is provided. (Level A)
3.12.2 Outline View: An
"outline" view of rendered content is provided,
composed of labels for important structural elements (e.g., heading text,
table titles, form titles, and other labels that are part of the content).
(Level AA)
Note: 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, and the title attribute is a label for its element.
3.12.3 Configure Set of Important
Elements: The user has the option to configure the set of important elements for the "outline" view,
including by element type (e.g., headers). (Level AAA)
3.13.1 Basic Link
Information: The following information is provided for each link
(Level A):
- (a) link element content,
- (e) new viewport: whether the author has specified that the resource will open
in a new viewport.
3.13.2 Extended Link
Information: The following information is provided for each link
(Level AAA):
- link title,
- technology type: of the linked Web resource,
- internal/external: whether the link
is internal to the resource (e.g., the link is to a target in the same
Web page),
PRINCIPLE 4. Ensure that the user interface is
operable
4.1.1 Keyboard Operation: All
functionality can be operated via the keyboard using sequential or direct
keyboard commands that do not require specific timings for individual
keystrokes, except where the underlying function requires input that depends
on the path of the user's movement and not just the endpoints (e.g., free
hand drawing). This does not forbid and should not discourage providing mouse
input or other input methods in addition to keyboard operation. (Level A)
4.1.2 Keystroke Precedence: The user has
the option to specify that keystrokes be processed in the following order:
user agent user interface, user agent extensions, content keystroke
operations administered by the user agent (e.g., access keys), and executable
content (e.g., key press events in scripts, etc.). (Level A)
4.1.3 No Keyboard Trap (Minimum): The user
agent prevents keyboard traps as follows (Level A):
- (a) in the UI: if keyboard focus can be
moved to a component using the keyboard, then focus can be moved away
from that component using standard sequential keyboard commands (e.g.,
TAB key)
- (b) in the rendered content: provides a
documented direct keyboard command that will always restore keyboard
focus to a known location (e.g., the address bar).
- (c) in the rendered content: provides a
documented direct keyboard command that will always move keyboard focus
to a subsequent focusable element
4.1.4 Separate Selection from
Activation: The user has the option to
have selection separate from activation (e.g., navigating through a set of radio buttons without changing
which is the active/selected option). (Level A)
4.1.5 Standard Text Area Navigation
Conventions: Views that render text support the standard text area
conventions for the operating environment, including, but not necessarily limited to:
character keys, backspace/delete, insert, "arrow" key navigation (e.g.,
"caret" browsing), page up/page down, navigate to start/end, navigate by
paragraph, shift-to-select mechanism, etc. (Level A)
4.1.6 Present Direct Commands in Rendered Content: The user has the option to have any recognized direct commands (e.g. accesskey) in rendered content be presented with their associated elements (e.g. "[Ctrl+t]" displayed after a link whose accesskey value is "t", or an audio browser reading the value or label of a form control followed by "accesskey control plus t"). (Level A)
4.1.7 Present Direct Commands in User Interface: The user has the option to have any direct commands (e.g. keyboard shortcuts) in the user agent user interface be presented with their associated user interface controls (e.g. "Ctrl+S" displayed on the "Save" menu item and toolbar button). (Level AA)
4.1.8 Keyboard Navigation:
The user can use the keyboard to navigate from group to group of focusable
items and to traverse forwards and backwards all of the focusable items
within each group. Groups include, but are not limited to, toolbars, panels,
and user agent extensions. (Level AA)
4.1.9 Important Command Functions: Important command functions (e.g. related to navigation, display, content, information management, etc.) are available using a single or sequence of keystrokes or key combinations. (Level AA)
4.1.10 Override of UI Keyboard Commands:
The user can override any keyboard shortcut binding for the user agent user
interface except for conventional bindings for the operating environment
(e.g., for access to help). The rebinding options must include single-key and
key-plus-modifier keys if available in the operating environment. (Level
AA)
4.1.11 User Override of Accesskeys: The
user can override any recognized author supplied content keybinding (i.e. access key). The user must have an option to save the
override of user interface keyboard shortcuts so that the rebinding persists
beyond the current session. (Level AA)
4.1.12 Specify preferred keystrokes: The
user can override any keyboard shortcut including recognized author supplied shortcuts (e.g
accesskeys) and user interface controls, except for conventional bindings for
the operating environment (e.g., for access to help). (Level
AA)
4.2.1 List event handlers: The user can, through keyboard input alone, have presented the list of input device event handlers explicitly associated with the content focus element. (Level A)
4.2.2 Activate any event handler: The
user can, through keyboard input alone, activate any
input device event handlers explicitly
associated with the
content focus element. (Level A)
4.2.3 Activate all event handlers: The user can, through keyboard input alone, simultaneously activate all input device event handlers explicitly associated with the
content focus element. (Level A)
4.3.1 Timing Adjustable:
Where time limits for user input are recognized
and controllable by the user agent, an option is provided to extend the time
limit. (Level A)
Guideline 4.4 Help users avoid flashing that could cause seizures. [Implementing 4.4]
4.4.1 Three Flashes or Below Threshold: In its default configuration, the user agent does not display any user interface components or recognized content that flashes more than three times in any one second period, unless the flash is below the general flash and red flash thresholds. (Level A)
4.4.2 Three Flashes: In its default configuration, the user agent does not display any user interface components or recognized content that flashes more than three times in any one second period (regardless of whether not the flash is below the general flash and red flash thresholds). (Level AAA) [WCAG 2.0]
Guideline
4.5 Configure and store preference settings.
4.5.1 Change Preference Settings The user has the option to change settings that impact accessibility. (Level A)
4.5.2 Persistent Accessibility Settings: User agent accessibility preference settings persist between sessions. (Level A)
4.5.3 Multiple Sets of Preference Settings: The
user can save and retrieve multiple sets of user agent preference settings.
(Level AA)
4.5.4 Portable Preference Settings:The user can transfer preference settings across locations onto a compatible system. (Level AAA)
4.5.5 Preferences Wizard: A
wizard helps the user to configure (at least) the accessibility-related
user agent preferences. (Level AAA)
4.5.6 Restore all to default. The user can restore all preference settings to their default values. (Level A)
4.5.7 Restore related preferences to default. The user can restore groups of related preference settings to their default values (e.g. reset keyboard shortcuts, reset colors and sizes of rendered content, etc.). (Level AA)
4.5.8 Change preference setting outside the UI: The user can adjust preference settings from outside the user agent user interface. (Level AA)
4.6.1 Find:The user can perform a search within rendered content (e.g., not hidden with a style), including text alternatives, for any sequence of characters from the document character set set. (Level A)
4.6.2 Find Direction: The user has the option of searching forward or backward from the focused location in content. The user will be notified of changes in search direction; and when the search reaches the upper or lower extent of the content based on the search direction. (Level A)
4.6.3 Match Found: When there is a match, the user is alerted and the viewport moves so that the matched text content is at least partially within it. The user can search for the next instance of the text from the location of the match.
4.6.4 Alert on No Match: The user is
notified 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). (Level
A)
4.6.5 Advanced Find: The user agent provides an accessible advanced
search facility, with a case sensitive and case-insensitive search
option, and the ability for the user to perform a search within all
content (including hidden content and captioning) for text and text
alternatives, for any sequence of characters from the document character
set. (Level AA)
4.7.1 Structured Navigation:
Forward and backward sequential navigation over important (structural) elements in rendered content is provided. (Level
A)
4.7.2 Direct navigation: direct movement to important (structural and
operable) elements in rendered content is provided. (Level A).
4.7.3 Direct activation: direct movement to and activation of any operable
elements in rendered content is provided. (Level AA)
4.7.4 Configure Set of Important Elements: The user has the option to
configure the set of important elements for structured navigation, including
by element type (e.g., headers, list items, images). (Level AAA) @@Editor's
note: Review the definition of "important elements" @@
4.7.5 Discover navigation and activation keystrokes: Direct navigation and activation keystrokes are discoverable both
programmatically and via perceivable labels. (Level A)
4.7.2OLD @@Editor's note: Review the definition of "important elements" @@
Note: For example, allow the user to navigate only
paragraphs, or only headings and paragraphs, or to suppress and restore
navigation bars, or to navigate within and among tables and table cells
Guideline 4.8 Provide toolbar
configuration.
4.8.1 Configure Position:
For graphical user agent user interfaces
with toolbars, the user can add, remove and configure the
position of user agent user interface
controls on those toolbars from a pre-defined set of controls. (Level
AAA)
4.8.2 Restore Default Toolbars: The
user can restore the default toolbar configuration. (Level AAA)
Guideline 4.9 Provide control of
content that may reduce accessibility.
4.9.1 Background Image
Toggle: The user has the global option
to hide/show background images. (Level
A)
4.9.2 Time-Based Media
Load-Only: The user has the option to
load time-based media content @@DEFINE@@
such that the first frame is displayed (if video), but the content is not
played until explicit user request. (Level
A)
4.9.3 Execution
Placeholder: The user has the option to
render a placeholder instead of executable
content that would normally be contained within an on-screen area (e.g.,
Applet, Flash), until explicit user request to
execute. (Level A)
4.9.4 Execution Toggle: The
user has the option to turn on/off the execution
of executable content that would not normally be contained within a
particular area (e.g., Javascript). (Level A)
4.9.5 Playback Rate Adjustment for Prerecorded Content: The user can adjust the playback rate of prerecorded time-based media content, such that all of the following are true (Level A):
- The user can adjust the playback rate of the time-based media tracks to between 50% and 250% of real time.
- Speech whose playback rate has been adjusted by the user maintains pitch in order to limit degradation of the speech quality.
- Audio and video tracks remain synchronized across this required range of playback rates.
- The user agent provides a function that resets the playback rate to normal (100%).
4.9.6 Stop/Pause/Resume
Multimedia: The user can 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. (Level A)
4.9.6 Navigate Multimedia:The user can navigate along the timebase using a continuous scale, and by relative time units within rendered audio and animations (including video and animated images) that last three or more seconds at their default playback rate. (Level A)
4.9.7 Semantic Navigation of Time-Based Media. The user can navigate by semantic structure within the time-based media, such as by chapters or scenes, if present in the media (AA).
4.9.8 Track Enable/Disable of Time-Based Media. During time-based media playback, the user can determine which tracks are available and select or deselect tracks. These selections may override global default settings for captions, audio descriptions, etc.
4.9.9 Sizing Playback Viewport: User has the ability to adjust the size of the time-based media up to the full height or width of the containing viewport, with the ability to preserve aspect ratio and to adjust the size of the playback viewport to avoid cropping, within the scaling limitations imposed by the media itself. (Level AA)
4.9.10 Scale and position alternative media tracks. User has ability to scale and position alternative media tracks independent of base video. (Level AAA)
4.9.1113 Adjust Playback Contrast and Brightness. User has ability to control the contrast and brightness of the content within the playback viewport.
Applicability Notes:
The guideline only applies to images, animations, video, audio, etc. that
the user agent can recognize.
If the browser is playing the video natively, then there is only 1 user agent. Then it falls on the browser to meet the UAAG spec.
If author uses windows media player inside the video element, the browser needs to map its native controls to the embedded wmp controls, and provide access to all the controls.
User needs to be able to define rendering parameters of playback at rendertime.
Principle 5: Ensure that user interface is
understandable
Guideline 5.1 Help users avoid
unnecessary messages. [Implementing 5.1]
5.1.1 Option to Ignore: The
user has the option to turn off rendering of
non-essential or low priority text messages or updating/changing information in the content based on priority properties
defined by the author (e.g., ignoring updating content
marked "polite" ). (Level AA)
Guideline 5.2 Help users avoid and correct
mistakes.
5.2.1 Form Submission:The user has the ability to set a global option disable any
form submission made by a control that is not the submit control (e.g.
forms that submit when Enter is pressed). Should login be an exception? (Level AA)
Guideline 5.3 Document the user agent user
interface including all accessibility features.
5.3.1 Accessible Format: At
least one version of the documentation is either (Level A):
- (a) "A" accessible: Web content and
conforms to WCAG 2.0 Level "A" (although it is not necessary for the
documentation to be delivered on-line), or,
- (b) accessible platform format: not Web
content and conforms to a published accessibility benchmark that is
identified in the conformance claim (e.g.,
when platform-specific documentation systems are used).
5.3.2 Document Accessibility
Features: All user agent features
that benefit accessibility @@DEFINE - as specified
in the conformance claim@@ are documented. (Level A)
5.3.3 Changes Between
Versions: Changes to features that
affect accessibility since the previous version of the user agent are
documented. (Level AA)
5.3.4 Centralized
View: There is a centralized view
of all features of the user agent that benefit accessibility, in a dedicated
section of the documentation. (Level AA)
5.3.5 Context Sensitive
Help: There is context-sensitive
help on all user agent features that benefit accessibility. (Level AAA)
5.3.6 Appropriate Language If characteristics of your user agent involve producing an end user experience such as speech, you need to react appropriately to language changes.
5.4 The user agent must behave in a predictable fashion.
5.4.1 Control default focus: A user agent provides a mechanism for setting global configuration of whether web pages can set default focus.
5.4.2 Unpredictable focus: Don't move the focus without telling the user. Provide a global option to block uninitiated focus changes.
Missing: Greater ease in interpreting security messaging. Should be cross-referenced with the security working group.
This section is normative.
Conformance means that the user agent satisfies the success criteria
defined in the guidelines section. This conformance section describes
conformance and lists the conformance requirements.
In order for a Web page to conform to UAAG 2.0, one of the following levels of conformance is met
in full.
Note 1: Although conformance can only be achieved at the stated levels,
developers are encouraged to report (in their claim) any progress toward
meeting success criteria from all levels beyond the achieved level of
conformance.
If a conformance claim is made, then the conformance claim must meet the
following conditions and include the following information (user agents
can conform to UAAG 2.0 without making a claim):
A description of how the UAAG 2.0 success criteria were met where this
may not be obvious.
Developers of user agents that do not yet conform fully to a particular
UAAG 2.0 conformance level are encouraged to publish a statement on
progress towards conformance. This statement would be the same as a
conformance claim except that this statement would specify an UAAG 2.0
conformance level that is being progressed towards, rather than one
already satisfied, and report the progress on success criteria not yet
met. The author of a "Progress Towards Conformance" Statement is solely
responsible for the accuracy of their statement. Developers are
encouraged to provide expected timelines for meeting outstanding success
criteria within the Statement.
Neither W3C, WAI, nor UAWG take any responsibility for any aspect or
result of any UAAG 2.0 conformance claim that has not been published
under the authority of the W3C, WAI, or UAWG.
- activate
- To execute or carry out the behaviors associated
with an enabled element in the rendered
content or component of the user agent user
interface.
- alternative content
- Content that is used in place of other content that a person may not be able to access. Alternative content fulfills essentially the same function or purpose as the original content. Examples include text alternatives for non-text content, captions for audio, audio descriptions for video, sign language for audio, media alternatives for time-based media. See WCAG for more information.
- alternative content
stack:
- The set of alternative content items for a
given position in content. The items may be mutually exclusive (e.g.,
regular contrast graphic vs. high contrast graphic) or non-exclusive
(e.g., caption track that can play at the same time as a sound
track).
- animation
- Graphical content that is rendered such that it can automatically change over time, potentially giving the user a visual perception of movement. Examples include video, animated images, scrolling text, programmatic animation (e.g., moving or replacing rendered objects).
-
- application
programming interface (API), conventional input/output/device
API
- An application programming interface (API) defines how
communication may take place between applications.
- assistive technology
- An assistive
technology:
- relies on services (such as retrieving Web
resources and parsing markup) 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, and
content transformations (e.g., to make tables more accessible).
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. These
technologies include wheelchairs, reading machines, devices for
grasping, text telephones, and vibrating pagers. 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.
- audio
- The technology of sound reproduction. Audio can be created synthetically (including speech synthesis), streamed from a live source (such as a radio broadcast), or recorded from real world sounds.
-
- audio description - also called
described video, video description and descriptive narration
- An equivalent alternative that takes the form of narration added to
the audio to describe important visual details
that cannot be understood from the main soundtrack alone. Audio
description of video provides information about actions, characters,
scene changes, on-screen text, and other visual content. In standard
audio description, narration is added during existing pauses in
dialogue. In extended audio
description, the video is paused so that there is time to add
additional description.
- authors
- The people who have worked either alone or collaboratively to create
the content (includes content authors, designers, programmers,
publishers, testers, etc.).
- author styles
- Style property
values that are set by the author as part of the content.
- background images
- Images that are rendered on the base background.
- base
background
- The background of the content as a whole, such that
no content may be layered behind it. In graphics applications, the base
background is often referred to as the canvas.).
- blinking
text
- Text whose visual rendering alternates between visible and invisible
at any rate of change.
- captions
- An equivalent alternative that takes the form of text presented and synchronized with time-based media to provide not only the speech, but also non-speech information conveyed through sound, including meaningful sound effects and identification of speakers. In some
countries, the term "subtitle" is used to refer to dialogue only and
"captions" is used as the term for dialogue plus sounds and speaker
identification. In other countries, "subtitle" (or its translation) is
used to refer to both. Open captions are captions that are
always rendered with a visual track; they cannot be turned off.
Closed captions are 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.
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.
- 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.
-
-
- content (Web content)
- Information and sensory experience to be communicated to the user by means of a user agent, including code or markup that defines the content's structure, presentation, and interactions [adapted from WCAG 2.0]
empty
content (which may be alternative 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).
-
document object, Document Object Model
(DOM)
- The Document Object Model is a platform- and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure and style of documents. The document can be further processed and the results of that processing can be incorporated back into the presented page. This is an overview of DOM-related materials here at W3C and around the web:
http://www.w3.org/DOM/#what.
- document source, text source
- Text the user agent renders upon user request to view the source of specific viewport content (i.e. selected content, frame, page).
- documentation
- Any information that supports the use of a user agent. This information may be found, for example, in manuals, installation instructions, the help system, and tutorials. Documentation may be distributed (e.g., as files installed as part of the installation, some parts may be delivered on CD-ROM, others on the Web). See guideline 5.3 for information about
documentation.
- element, element type
- This document uses the terms "element" and "element
type" primarily 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 element with associated behaviors that can 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 elements defined by implemented markup languages. A disabled element is a potentially enabled element, that is not currently available for activation (e.g., a "grayed out" menu item).
- equivalent alternative
- Content that is an acceptable substitute for other content that a person may not be able to access. An equivalent alternative fulfills essentially the same function or purpose as the original content upon presentation:
- text alternative [WCAG 2.0]: text that is available via the operating environment that is used in place of non-text content (e.g., text equivalents for images, text transcripts for audio tracks, or collated text transcripts for a movie).
- full text alternative for synchronized media including any interaction [WCAG 2.0]: document including correctly sequenced text descriptions of all visual settings, actions, speakers, and non-speech sounds, and transcript of all dialogue combined with a means of achieving any outcomes that are achieved using interaction (if any) during the synchronized media.
- synchronized alternatives: present essential audio information visually (i.e., captions) and essential video information in an auditory manner (i.e., audio descriptions).
[from ATAG 2.0]
- 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
events, changes to content, loading of content, and requests from the
operating environment.
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 through scripting, markup or the DOM.
- explicit user request
- Any user interaction by the user through the user
agent user interface, 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 can make errors when interacting with the user agent. For example, a user may inadvertently respond "yes" to a prompt instead of "no." In this document, this type of error is still considered an explicit user request.
- focus, content focus, user interface focus, current
focus
- In this document, the term "content focus" 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, i.e., it may be "set" on an enabled element,
programmatically or through the user interface. Some content
specifications (e.g., HTML, CSS) allow authors to associate
behavior with focus set and unset events.
- 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, designers of word
processing software 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., a radio button, text
box, or menu).
On the screen, the user agent may highlight the
content focus in a variety of ways, including through colors, fonts,
graphics, and magnification. The user agent may also highlight the
content focus 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.
- globally, global configuration
- @@Editors' Note: Needs to be written@@
- graphical
- Information (including text, colors, graphics, images, and animations)
rendered for visual consumption.
- highlight
- 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
- Pictorial content that is static (i.e.not moving or changing). See also the definition of animation.
- important elements
- 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). Refer to the Implementing document [Implementing UAAG 2.0] for information
about identifying and navigating important elements. @@ Ed Note: Update links
- input configuration
- The set of "bindings"
between user agent functionalities and user
interface input mechanisms (e.g., menus, buttons, keyboard keys,
and voice commands). The default input configuration is the set of
bindings the user finds after installation of the software. Input
configurations may be affected by author-specified bindings (e.g.,
through the
accesskey attribute of HTML 4 [HTML4]).
-
- keyboard command
- Direct Commands* (also called keyboard shortcuts or accelerator keys) are those tied to particular UI controls or application functions, allowing the user to navigate-to or activate them without traversing any intervening controls (e.g., "ctrl"+"S" to save a document). It is sometimes useful to distinguish direct commands that are associated with controls that are rendered in the current context (e.g., "alt"+"D" to move focus to the address bar) from those that may be able to activate program functionality that is not associated with any currently rendered controls (e.g., "F1" to open the Help system). Direct commands help users accelerate their selections.
- 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 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 [WCAG 2.0, ATAG
2.0]
- 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.
- notify
- To make the user aware of events or status changes. Notifications can occur within the user agent user interface (e.g., status bar) or within the content display. Notifications may be passive and not require user acknowledgment, or they may be presented in the form of a prompt requesting a user response (e.g., a confirmation dialog).
- 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. Placeholders should identify
the technology of the object of which it is holding the place.
Placeholders will appear in the alternative content stack.
- platform accessibility
architecture
- A programmatic interface that is specifically engineered to enhance
communication between mainstream software applications and assistive
technologies (e.g., MSAA, UI Automation, and IAccessible2 for Windows applications, AXAPI for MacOSX applications, Gnome Accessibility Toolkit API for Gnome applications, Java Access for Java applications, etc.). On some platforms it may be conventional to enhance
communication further via implementing a DOM.
- plug-in [ATAG 2.0]
- 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 during an audio
rendering or a cursor position 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, and selection. The stability of the point
of regard is addressed by @@.
- 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, and
natural language preferences. In operating environments
with distinct user accounts, profiles enable users to reconfigure
software quickly when they log on. Users may share their profiles with
one another. Platform-independent profiles are useful for those who use
the same user agent on different platforms.
- prompt [ATAG
2.0]
- Any user agent initiated request for a decision or piece of
information from users.
- 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, or on a mobile device. Style information (e.g., fonts, colors,
and synthesized speech prosody) 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 at
installation is called the property's default value.
- recognize
- Authors encode information in many ways, including
in markup languages, style sheet languages, scripting languages, and
protocols. 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 a
heading using a visual effect alone (e.g., just 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 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.
The Techniques document [UAAG10-TECHS] lists
some markup known to affect accessibility that user agents can
recognize.
- 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 is not rendered but that may
influence the graphical rendering (e.g., layout) of other content.
Similarly, silent content is content that
is not rendered but that may influence the audio rendering of other
content. 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" refers to the text portion of repair
content. Some error conditions that may lead to the generation of
repair content include:
- Erroneous or incomplete content (e.g., ill-formed markup, invalid
markup, or missing alternative 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, or 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 guidelines 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 (programming) 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 (possibly empty) range of content. Generally, user agents limit
the type of content that may be selected to text content (e.g., one or
more fragments of text). In some user agents, the value of the selection is constrained by the
structure of the document tree.
On the screen, the selection may be highlighted in
a variety of ways, including through colors, fonts, graphics, and
magnification. 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, including for
cut and paste operations, to designate a specific element in a document
for the purposes of a query, and as an indication of point of regard.
The selection has state, i.e., it may be "set," 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.
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. 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 or a particular scripting
language), 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.
- synchronize
- In this document, "to synchronize" refers to the act
of time-coordinating two or more presentation components (e.g., a visual track with captions, or
several tracks in a multimedia presentation). 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.
- technology (Web content) - or
shortened to technology [WCAG 2.0, ATAG
2.0]
- A mechanism for encoding instructions to be rendered, played or
executed by user agents. Web Content
technologies may include markup languages, data formats, or programming
languages that authors may use alone or in
combination to create end-user experiences that range from static Web
pages to multimedia presentations to dynamic Web applications. Some
common examples of Web content technologies include HTML, CSS, SVG,
PNG, PDF, Flash, and JavaScript.
- 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 alternative 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 format
- 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, or
any media object identified by Internet media type to be an XML
document (as defined in [XML], section 2) or SGML
application. Refer, for example, to Internet media types defined in
"XML Media Types" [RFC3023].
- 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.
- track (audio track or
visual track)
- Content rendered as sound through an
audio viewport. The audio track may be all
or part of the audio portion presentation (e.g., each instrument may
have a track, or each stereo channel may have a track). Also see definition of visual track
- user agent
- A user agent is any software that retrieves, renders
and facilitates end user interaction with 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 content in that markup
language; others do not. 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, and applets.
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 @@.
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.
- view, viewport
- The user agent renders content through one or
more viewports. Viewports include windows, frames, pieces of paper,
loudspeakers, and virtual magnifying glasses. A viewport may contain
another viewport (e.g., nested frames). User
agent user interface controls such as prompts, menus, and alerts
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.
"top-level" viewports are
viewports that are not contained within other user agent viewports.
- 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
- Anything that can be identified by a Uniform Resource Identifier
(URI).
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This publication has been funded in part with Federal funds from the U.S.
Department of Education, National Institute on Disability and Rehabilitation
Research (NIDRR) under contract number ED05CO0039. The content of this
publication does not necessarily reflect the views or policies of the U.S.
Department of Education, nor does mention of trade names, commercial
products, or organizations imply endorsement by the U.S. Government.
@@Ed. This section is still under development@@
@@Ed. This section is still under development@@