4. Glossary

4. Glossary
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User Agent Accessibility Guidelines 1.0
17 December 2002
4.
Glossary
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.
· b ·
· j · k · l · m ·
· q ·
· x · y · z
Activate
In this document, the verb "to activate" means (depending
on context) either:
To execute or carry out one or more behaviors associated with an
enabled element
To execute or carry out one or more behaviors associated with a component
of the
user agent user
interface
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 explicit 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, or video card.
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, the conventional input
APIs
of the
target user agent
are for the mouse and
keyboard. For touch screen devices or mobile devices, conventional input
APIs
may include stylus, buttons, and voice. 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
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.
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
(checkpoints
2.3
and
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, or via style sheets or scripts). The results of "configuration" might not
take effect immediately (e.g., due to time spent reinitializing the system,
initiating a new session, or 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 can 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).
global configuration
is one
that applies across elements of the same Web resource, as well as across Web
resources.
User agents may allow users to choose configurations based on various
parameters, such as hardware capabilities or natural language preferences.
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
In this document, device-independence refers to the
desirable property that operation of a user agent feature is not bound to only
one 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 (e.g., from style sheets, scripts, or transformations),
produced as a result of preferences set within the user agent, or added as the
result of a repair performed automatically by the user agent. 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
and
id
. Most of the requirements of this
document apply to the document object after its construction. However, a few
checkpoints (e.g., checkpoints
2.7
and
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.
Document character set
In this document, a document character set (a concept from
SGML) is a collection of abstract characters that a format specification allows
to appear in an instance of the format. A document character set consists of:
A "repertoire": A set of abstract characters, such as the Latin letter "A,"
the Cyrillic letter "I," and the Chinese character meaning "water."
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 the
text
portion of
the document source.
Documentation
Documentation refers to 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., some parts may be delivered on CD-ROM, others on the Web).
See
guideline 12
for information about documentation requirements.
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 enabled element is a piece of
content
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
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
"grayed 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 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
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 instead of "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, 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.
Graphical
In this document, the term "graphical" refers to
information (including text, colors, graphics, images, and animations) 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, and voice commands). The default input
configuration is the set of bindings the user finds after installation of the
software; see
checkpoint 12.3
for relevant documentation requirements.
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
[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
[HTML4]
section 8.1), the
xml:lang
attribute in
XML
1.0
[XML]
, section 2.12), the
hreflang
attribute
for links in
HTML
[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.
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 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
guideline 5
and
checkpoint
9.4
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
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," "never prompt me before doing X," "never do
X but tell me when you could have," and "never do X and never tell me that you
could have."
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
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, 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 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 (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.
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
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.
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 this
document. 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 content in that markup language;
others do not. For example,
XML
1.0
[XML]
does not specify default styles
for XML documents.
HTML
[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.
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]
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