- Activate
- In this document, the verb "to activate" means (depending
on context) either:
The effect of activation depends on the type of enabled element or user
interface control. For instance, when a link is activated, the user agent
generally retrieves the linked Web
resource. When a form element is activated, it may change state
(e.g., check boxes) or may take user input (e.g., a text entry field).
-
Alert
- In this document, "to alert" means to make the user aware
of some event, without requiring acknowledgement. For example, the user agent
may alert the user that new content is available on the server by displaying a
text message in the user agent's status bar.
See checkpoint 1.3
for requirements about alerts.
-
Animation
- In this document, an "animation" refers to content that, when rendered, creates a visual
movement effect automatically (i.e., without manual user interaction). This
definition of animation includes video and animated images. Animation
techniques include:
- graphically displaying a sequence of snapshots within the same region
(e.g., as is done for video and animated images). The series of snapshots may
be provided by a single resource (e.g., an animated GIF image) or from distinct
resources (e.g., a series of images downloaded continuously by the user
agent).
- scrolling text (e.g., achieved through markup or style sheets).
- displacing graphical objects around the viewport (e.g., a picture of a ball
that is moved around the viewport giving the impression that it is bouncing off
of the viewport edges). For instance, the SMIL 2.0
[SMIL20] animation modules explain how to create such animation
effects in a declarative manner (i.e., not by composition of successive
snapshots).
-
Applet
- An applet is a program (generally written in the Java
programming language) that is part of content,
and that the user agent executes.
- Application
Programming Interface (API), conventional input/output/device
API
- An application programming interface (API) defines how
communication may take place between applications.
Implementing APIs that are independent of a particular operating environment
(as are the W3C DOM Level 2 specifications) may reduce implementation costs for
multi-platform user agents and promote the development of multi-platform
assistive technologies. Implementing conventional APIs for a particular
operating environment may reduce implementation costs for assistive technology
developers who wish to interoperate with more than one piece of software
running on that operating environment.
A "device API" defines how communication may take place
with an input or output device such as a keyboard, mouse, video card, etc.
In this document, an "input/output API" defines how
applications or devices communicate with a user agent. As used in this
document, input and output APIs include, but are not limited to, device APIs.
Input and output APIs also include more abstract communication interfaces than
those specified by device APIs. A "conventional input/output API" is one that
is expected to be implemented by software running on a particular operating
environment. For example, on desktop computers today, the conventional input
APIs are for the mouse and keyboard. For touch screen
devices or mobile devices, conventional input APIs may
include stylus, buttons, voice, etc. The graphical display and sound card are
considered conventional ouput devices for a graphical desktop computer
environment, and each has an associated API.
- Assistive technology
- In the context of this document, an assistive technology
is a
user agent that:
- relies on services (such as retrieving
Web resources, parsing markup, etc.) provided by one or more other
"host" user agents. Assistive technologies communicate data and messages with
host user agents by using and monitoring APIs.
- provides services beyond those offered by the host user agents to meet the
requirements of users with disabilities. Additional services include
alternative renderings (e.g., as synthesized speech or magnified content),
alternative input methods (e.g., voice), additional navigation or orientation
mechanisms, content transformations (e.g., to make tables more accessible),
etc.
For example, screen reader software is an assistive technology because it
relies on browsers or other software to enable Web access, particularly for
people with visual and learning disabilities.
Examples of assistive technologies that are important in the context of this
document include the following:
- screen magnifiers, which are used by people with visual disabilities to
enlarge and change colors on the screen to improve the visual readability of
rendered text and images.
- screen readers, which are used by people who are blind or have reading
disabilities to read textual information through synthesized speech or braille
displays.
- voice recognition software, which may be used by people who have some
physical disabilities.
- alternative keyboards, which are used by people with certain physical
disabilities to simulate the keyboard.
- alternative pointing devices, which are used by people with certain
physical disabilities to simulate mouse pointing and button activations.
- Beyond this document, assistive technologies consist of
software or hardware that has been specifically designed to assist people with
disabilities in carrying out daily activities, e.g., wheelchairs, reading
machines, devices for grasping, text telephones, vibrating pagers, etc. For
example, the following very general definition of "assistive technology device"
comes from the (U.S.) Assistive Technology Act of 1998
[AT1998]:
Any item, piece of equipment, or product system, whether acquired
commercially, modified, or customized, that is used to increase, maintain, or
improve functional capabilities of individuals with disabilities.
-
Attribute
- This document uses the term "attribute" in the XML sense:
an element may have a set of attribute specifications (refer to the XML 1.0
specification [XML] section 3).
-
Audio
- In this document, the term "audio" refers to content that
encodes pre-recorded 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).
- Auditory description
- An auditory description (sometimes, "audio description")
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 auditory description is
synchronized with (and possibly included as part of) the audio track of the presentation, usually during
natural pauses in the audio
track. Auditory 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 (sometimes, "closed 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 above, below, or superimposed over video.
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. Please 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 auditory
description. Collated text transcripts are essential for individuals
who are deaf-blind.
- Conditional content
- Conditional content is content that, by format
specification, should be made available to users through the user interface,
generally under certain conditions (e.g., based on user preferences or
operating environment limitations). Some examples of conditional content
mechanisms include:
- The "
alt" attribute of the IMG element in HTML 4.
According to
section 13.2 of the HTML 4 specification ([HTML4]): "User agents must render
alternate text when they cannot support images, they cannot support a certain
image type or when they are configured not to display images.
OBJECT elements in HTML 4.
Section 13.3.1 of the HTML 4 specification ([HTML4]) explains the conditional
rendering rules of (nested) OBJECT elements. The rules select
among ordered alternatives according to user preferences or error
conditions.- The
switch element and test attributes in SMIL 1.0. Sections
4.3 and 4.4, respectively,
of SMIL 1.0 [SMIL] explain the conditional
rendering rules of these features.
- SVG 1.0 [SVG] also includes a
switch element and several attributes for conditional processing.
- The
NOSCRIPT and NOFRAMES elements in HTML 4
[HTML4] allow the author to provide content under conditions when
the user agent does not support scripts or frames, or the user has turned off
support for scripts or frames.
Specifications vary in how completely they define how and when to render
conditional content. For instance, the HTML 4 specification includes the
rendering conditions for the "alt" attribute, but not for the
"title" attribute. The HTML 4 specification does indicate that the
"title" attribute should be available to users through the user
interface ("Values of the title attribute may be rendered by user agents in a
variety of ways...").
Note: The Web Content Accessibility Guidelines 1.0 requires
that authors provide text equivalents for non-text content. This is generally
done by using the conditional content mechanisms of a markup language. Since
conditional content may not be rendered by default, the current document
requires the user agent to provide access to unrendered conditional content (checkpoint
2.3 and checkpoint 2.9) as it may have been provided to promote
accessibility.
-
Configure,
control
- In the context of this document, the verbs "to control"
and "to configure" share in common the idea of governance such as a user may
exercise over interface layout, user agent behavior, rendering style, and other
parameters required by this document. Generally, the difference in the terms
centers on the idea of persistence. When a user makes a change by
"controlling" a setting, that change usually does not persist beyond that user
session. On the other hand, when a user "configures" a setting, that setting
typically persists into later user sessions. Furthermore, the term "control"
typically means that the change can be made easily (such as through a keyboard
shortcut) and that the results of the change occur immediately, whereas the
term "configure" typically means that making the change requires more time and
effort (such as making the change via a series of menus leading to a dialog
box, via style sheets or scripts, etc.) and that the results of the change may
not take effect immediately (e.g., due to time spent reinitializing the system,
initiating a new session, rebooting the system). In order to be able to
configure and control the user agent, the user needs to be able to "read" as
well as "write" values for these parameters. Configuration settings may be
stored in a profile.
The range and granularity of the changes that can be controlled or configured
by the user may depend on limitations of the
operating environment or hardware.
Both configuration and control may apply at different "levels": across
Web resources (i.e., at the user agent
level, or inherited from the operating environment), to the entirety of a
Web resource, or to components of a Web resource (e.g., on a per-element
basis).
A
global configuration is one that applies across elements of the
same Web resource, as well as across Web resources. A global configuration may
be implemented by more than one setting (e.g., per component of the user
agent). For instance, when a user agent consists of a browser that renders HTML
and a plug-in that renders SVG, to satisfy the global configuration
requirements of this document, the browser may provide one setting and the
plug-in another.
User agents may allow users to choose configurations based on various
parameters, such as hardware capabilities, natural language, etc.
Note: In this document, the noun "control" refers to a
component of the user
agent user interface.
-
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 context of the phrases non-text content and
text content.
Empty
content is either a null value or a string consisting of zero
characters. For instance, in HTML, "alt=''" sets the value of the
"alt" attribute to the empty string. In some markup languages, an
element may have empty content (e.g., the HR element in HTML).
- Device-independence
- Device-independence refers to the ability to make use of
software with any appropriate supported input or output device.
-
Document object,
Document Object Model (DOM)
- In general usage, the term "document object" refers to the user agent's
representation of data (e.g., a document). This data generally comes from the
document
source, but may also be generated (from style sheets, scripts,
transformations, etc.), produced as a result of preferences set within the user
agent, added as the result of a repair performed automatically by the user
agent, etc. Some data that is part of the document object is routinely
rendered (e.g., in HTML, what appears between the start and end tags
of elements and the values of attributes such as "alt", "title", and
"summary"). Other parts of the document object are generally processed by the
user agent without user awareness, such as DTD- or schema-defined names of
element types and attributes, and other attribute values such as "href", "id",
etc. These guidelines require that users have access to both kinds of data
through the user interface. Most of the requirements of this document apply to
the document object after its construction. However, a few checkpoints (e.g.,
checkpoint 2.7
and
checkpoint 2.11) may affect the construction of the document object.
A "document object model" is the abstraction that governs the construction
of the user agent's document object. The document object model employed by
different user agents may vary in implementation and sometimes in scope. This
specification requires that user agents implement the
APIs defined in Document Object Model
(DOM) Level 2 Specifications ([DOM2CORE] and
[DOM2STYLE]) for access to HTML,
XML, and CSS content. These DOM APIs allow authors
to access and modify the content via a scripting language (e.g., JavaScript) in
a consistent manner across different scripting languages. As a standard
interface, the DOM APIs make it easier not just for authors, but for assistive
technology developers to extract information and render it in ways most suited
to the needs of particular users.
-
Document character set
- A document character set (a concept taken from SGML) is a
sequence of abstract characters that may appear in Web content represented in a
particular format (such as HTML, XML, etc.). A document character set consists
of:
- a "repertoire", A set of abstract characters, such as the Latin letter "A",
the Cyrillic letter "I", the Chinese character meaning "water", etc.
- Code positions: A set of integer references to characters in the
repertoire.
For instance, the character set required by the HTML 4 specification
[HTML4] is defined in the Unicode specification
[UNICODE]. Refer to "Character Model for the World Wide Web"
[CHARMOD] for more information about document character sets.
-
Document source, text source
- In this document, the term "document source" refers to the
data that the user agent receives as the direct result of a request for a
Web resource (e.g., as the result of an
HTTP/1.1 [RFC2616] "GET", or as the result
of viewing a resource on the local file system). The document source generally
refers to the "payload" of the user agent's request, and doesn't generally
include information exchanged as part of the transfer protocol. The document
source is data that is prior to any repair by the user agent (e.g., prior to
repairing invalid markup). "Text source" refers to document source that is
composed of text.
-
Documentation
- Documentation refers to information that supports the use
of a user agent. This information may be found in manuals, installation
instructions, the help system, tutorials, etc. Documentation may be distributed
(e.g., some parts may be delivered on CD-ROM, others on the Web). Refer to guideline 12 for
information about documentation requirements.
- Element, element type,
- This document uses the terms "element" and "element type"
in the sense employed by the XML 1.0 specification ([XML],
section 3): an element type is a syntactic construct of a Document Type
Definition (DTD) for its application. This sense is also relevant to structures
defined by XML schemas. The document also uses the term "element" more
generally to mean a type of content (such as video or sound) or a logical
construct (such as a header or list).
-
Enabled element, disabled element
- An enabled element is a piece of
content with associated behaviors that may be activated through the
user interface or through an API. The set of elements that a user agent
enables is generally derived from, but is not limited to, the set of
interactive elements defined by implemented markup languages.
Some elements may only be enabled elements for part of a user session. For
instance, an element may be disabled by a script as the result of user
interaction. Or, an element may only be enabled during a given time period
(e.g., during part of a SMIL 1.0 [SMIL] presentation). Or, the user
may be viewing content in "read-only" mode, which may disable some
elements.
A disabled element is a piece of content
that is potentially an enabled element, but is not in the current session.
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; collated text transcripts for multimedia presentations and
animations) and non-text
equivalents (e.g., a prerecorded auditory description of a
visual track of a movie, or a sign
language video rendition of a written text, etc.).
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 (or portions of equivalents) 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
- User agents often perform a task when an event occurs that
is due to user interaction (e.g., document loading, mouse motion or a key
press, a request from the
operating environment, etc.). Some markup languages allow authors to
specify that a script, called an event handler, be executed when
the event 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 with a control
provided by the user
agent user interface (not those in content), the focus, or
selection. Control behavior should be
documented.
Some examples of explicit user requests include when the user selects "New
viewport", responds "Yes" to a prompt in the user agent's user interface,
configures the user agent to behave in a certain way, or changes the selection
or focus with the keyboard or pointing device.
Note: Users make mistakes. For example, a user may
inadvertently respond "yes" to a prompt when they meant "no." In this document,
this type of mistake is still considered an explicit user request.
- Fee link
- For the purpose of this document, the term "fee link"
refers to a link that when activated, debits the user's electronic "wallet"
(generally, a "micropayment"). The link's role as a fee link is identified
through markup (in a manner that the user agent can
recognize). This definition of fee link excludes payment mechanisms
(e.g., some form-based credit card transactions) that cannot be recognized by
the user agent as causing payments. For more information about fee links, refer
to "Common Markup for micropayment per-fee-links"
[MICROPAYMENT].
-
Focus,
content focus,
user interface focus, current focus
- In this document, the term "content focus" refers to a
user agent mechanism that satisfies 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.)
- The user may "set" content focus (programmatically or through the user
interface) on an enabled element without triggering the associated
behaviors.
- It has state. The user may prefer to always move the content focus manually
from one element to another.
- It may be used (programmatically or through the user interface) to trigger
the behaviors associated with an enabled element. This is generally implemented
by making the focus respond to input device events (often just keyboard
events).
User interface mechanisms may resemble content focus, but do not satisfy all
of the properties. For example, text editors often implement a "caret" that
indicates the current location of text input or editing. The caret may have
state and may respond to input device events, but it does not enable users to
activate the behaviors associated with enabled elements.
The user interface focus shares the properties of the content focus except
the first: the user interface focus designates zero or one control of the user agent user interface that has associated
behaviors (e.g., radio button, text box, menu, etc.).
On the screen, the content focus may be
highlighted using colors, fonts, graphics, magnification, etc. The
content focus may also be highlighted when rendered as synthesized speech, for
example through changes in speech prosody. The dimensions of the rendered
content focus may exceed those of the viewport.
In this document, each viewport is expected to have at most one content
focus and at most one user interface focus. This document includes requirements
for content focus only, for user interface focus only, and for both. When a
requirement refers to both, the term "focus" is used.
When several viewports
coexist, at most one viewport's content focus or user
interface focus responds to input events; this is called the current focus.
-
Graphical
- In this document, the term "graphical" refers to
information (text, colors, graphics, images, animations, etc.) rendered for
visual consumption.
- Highlight
- In this document, "to highlight" means to emphasize
through the user interface. For example, user agents highlight which content is
selected or focused. Graphical highlight mechanisms include dotted boxes,
underlining, and reverse video. Synthesized speech highlight mechanisms include
alterations of voice pitch and volume ("speech prosody").
- Image
- In this document, an "image" refers to content that encodes static (i.e., unmoving)
visual information. See also the definition of
animation.
- Input configuration
- An input configuration is the mapping of user agent
functionalities to some user
interface input mechanisms (e.g., menus, buttons, keyboard keys,
voice commands, etc.). The default input configuration is the mapping the user
finds after installation of the software; it must be documented (per checkpoint
12.3]). Input configurations may be affected by author-specified bindings
(e.g., through the "accesskey" attribute of HTML 4
[HTML4]).
- Interactive element,
non-interactive element,
- An interactive element is piece of content that, by
specification, may have associated behaviors to be executed or carried out as a
result of user or programmatic interaction. For instance, the interactive
elements of HTML 4
[HTML4] include: links, image maps, form elements, elements with a
value for the "longdesc" attribute, and elements with
event handlers explicitly associated with
them (e.g., through the various "on" attributes). The role of an element as an
interactive element is subject to
applicability. A non-interactive element is an element that, by format
specification, does not have associated behaviors. The expectation of this
document is that interactive elements become enabled elements in some sessions, and
non-interactive elements never become enabled elements.
- Natural language
- Natural language is spoken, written, or signed human
language such as French, Japanese, and American Sign Language. On the Web, the
natural language of content may
be specified by markup or HTTP headers. Some examples include the
"lang" attribute in HTML 4 ([HTML4] section 8.1), the "xml:lang"
attribute in XML 1.0 ([XML],
section 2.12), the
HTML 4 "hreflang" attribute for links in HTML 4
([HTML4], section 12.1.5), the HTTP
Content-Language header ([RFC2616], section 14.12) and the
Accept-Language request header ([RFC2616], section 14.4). See also
the definition of script.
-
Normative,
informative
- As used in this document, the term "normative" refers to
"that on which the requirements of this document depend for their most precise
statement." What is normative is required for conformance (though the conformance
scheme of this document allows claimants to exempt certain normative provisions
as long as the claim discloses the exemption). What is identified as
"informative" (sometimes, "non-normative") is never required for
conformance.
- Operating
environment
- The term "operating environment" refers to the environment
that governs the user agent's operation, whether it is an operating system or a
programming language environment such as Java.
-
Override
- In this document, the term "override" means that one
configuration or behavior preference prevails over another. Generally, the
requirements of this document involve user preferences prevailing over author
preferences and user agent default settings and behaviors. Preferences may be
multi-valued in general (e.g., the user prefers blue over red or yellow), and
include the special case of two values (e.g., turn on or off blinking text
content).
- Placeholder
- A placeholder is content generated by the user agent to
replace author-supplied content. A placeholder may be generated as the result
of a user preference (e.g., to not render images) or as
repair content (e.g., when an image
cannot be found). Placeholders can be any type of content, including text,
images, and audio cues.
This document includes requirements that the user be able to view the
original author-supplied content associated with a placeholder. To satisfy
these requirements, the user agent might render the content in place of the
placeholder or in a separate viewport (leaving the placeholder as is). A
request to view the original content associated with a placeholder is considered an explicit
user request to render that content.
This document does not require user agents to include placeholders in the document
object. A placeholder that is inserted in the document object should
conform to the Web Content Accessibility Guidelines 1.0
[WCAG10]. If a placeholder is not part of the document object, it is
part of the user interface only (and subject, for example, to checkpoint 1.3).
-
Plug-in
- A plug-in is a program that runs as part of the user agent
and that is not part of content.
Users generally choose to include or exclude plug-ins from their user
agent.
-
Point of regard
- The point of regard is a position in rendered
content that the user is presumed to be viewing. The dimensions of
the point of regard may vary. For example, it may be a point (e.g., a moment in
an audio rendering or a cursor in a graphical rendering), or a range of text
(e.g., focused text), or a two-dimensional area (e.g., content rendered through
a two-dimensional graphical viewport). The point of regard is almost always
within the viewport, but it may exceed the spatial or temporal dimensions of
the viewport (see the definition of rendered content for more information about
viewport dimensions). The point of regard may also refer to a particular moment
in time for content that changes over time (e.g., an
audio-only presentation). User agents may determine the point of
regard in a number of ways, including based on viewport position in content,
content focus,
selection, etc. A user agent should not change the point of regard
unexpectedly as this may disorient the user.
-
Profile
- A profile is a named and persistent representation of user preferences that
may be used to configure a user agent. Preferences include input
configurations, style preferences, natural language preferences, etc. In
operating environments with distinct user accounts, profiles enable
users to reconfigure software quickly when they log on, and profiles may be
shared by several users. Platform-independent profiles are useful for those who
use the same user agent on different platforms.
-
Prompt
- In this document, "to prompt" means to require input from
the user. The user agent should allow users to
configure how they wish to be prompted. For instance, for a user
agent functionality X, configurations might include: always prompt me before
doing X, always do X without prompting me, never do X but tell me when you
could have, never do X and never tell me that you could have, etc.
- Properties, values, and
defaults
- A user agent renders a document by applying formatting
algorithms and style information to the document's elements. Formatting depends
on a number of factors, including where the document is rendered: on screen, on
paper, through loudspeakers, on a braille display, on a mobile device, etc.
Style information (e.g., fonts, colors, synthesized speech prosody, etc.) may
come from the elements themselves (e.g., certain font and phrase elements in
HTML), from style sheets, or from user agent settings. For the purposes of
these guidelines, each formatting or style option is governed by a property and
each property may take one value from a set of legal values. Generally in this
document, the term "property"
has the meaning defined in CSS 2 ([CSS2], section 3). A reference to
"styles" in this document means a set of style-related properties.
- The value given to a property by a user agent when it is
installed is called the property's default value.
- Recognize
- Authors encode information in markup languages, style
sheet languages, scripting languages, protocols, etc. When the information is
encoded in a manner that allows the user agent to process it with certainty,
the user agent can "recognize" the information. For instance, HTML allows
authors to specify a heading with the H1 element, so a user agent that
implements HTML can recognize that content as a heading. If the author creates
headings using a visual effect alone (e.g., by increasing the font size), then
the author has encoded the heading in a manner that does not allow the user
agent to recognize it as a heading.
Some requirements of this document depend on content roles, content
relationships, timing relationships, and other information supplied by the
author. These requirements only apply
when the author has encoded that information in a manner that the user agent
can recognize. See the section on
conformance 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 influences graphical rendering of other content but is not
rendered itself. Similarly, "silent content" is content that
influences audio rendering of other content but is not rendered itself. Neither
invisible nor silent content is considered rendered content.
-
Repair content, repair text
- In this document, the term "repair content" refers to
content generated by the user agent in order to correct an error condition.
"Repair text" means repair content consisting only of
text. Some error conditions that may lead to the generation of
repair content include:
- Erroneous or incomplete content (e.g., ill-formed markup, invalid markup,
missing
conditional content that is required by format specification,
etc.);
- Missing resources for handling or rendering content (e.g., the user agent
lacks a font family to display some characters, the user agent doesn't
implement a particular scripting language, etc.);
This document does not require user agents to include repair content in the
document
object. Repair content inserted in the document object should
conform to the Web Content Accessibility Guidelines 1.0
[WCAG10]. For more information about repair techniques for Web
content and software, refer to "Techniques for Authoring Tool Accessibility
Guidelines 1.0" [ATAG10-TECHS].
- Script
- In this document, the term "script" almost always refers to a scripting
(programming) language used to create dynamic Web content. However, in
checkpoints referring to the written (natural) language of content, the term
"script" is used as in Unicode [UNICODE] to mean "A collection of
symbols used to represent textual information in one or more writing systems."
Information encoded in scripts may be difficult for a user agent to recognize For instance, a user agent is not
expected to recognize that, when executed, a script will calculate a factorial.
The user agent will be able to recognize some information in a script by virtue
of implementing the scripting language or a known program library (e.g., the
user agent is expected to recognize when a script will open a viewport or
retrieve a resource from the Web).
-
Selection, current selection
- In this document, the term "selection" refers to a user
agent mechanism for identifying a range of
content (e.g., text, images, etc.). Generally, user agents limit
selection to text content (e.g., one or more fragments of text). The selection may be structured (based on the
document tree) or unstructured (e.g., text-based). The range may be empty.
On the screen, the selection may be
highlighted using colors, fonts, graphics, magnification, etc. The
selection may also be highlighted when rendered as synthesized speech, for
example through changes in speech prosody. The dimensions of the rendered
selection may exceed those of the viewport.
The selection may be used for a variety of purposes: for cut and paste
operations, to designate a specific element in a document for the purposes of a
query, as an indication of point of
regard, etc.
The selection has state. 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 controls of the user agent user interface. The current document
only includes requirements for a content
selection mechanism.
-
Support,
implement,
conform
- In this document, the terms "support", "implement", and
"conform" all refer to what a developer has designed a user agent to do, but
they represent different degrees of specificity. A user agent "supports"
general classes of objects, such as "images" or "Japanese". A user agent
"implements" a specification (e.g., the PNG and SVG image format
specifications, a particular scripting language, etc.) or an
API (e.g., the DOM API) when it has been
programmed to follow all or part of a specification. A user agent "conforms to"
a specification when it implements the specification and satisfies its
conformance criteria. This document includes some conformance requirements to
other specifications (e.g., to a particular level of the "Web Content
Accessibility Guidelines 1.0" [WCAG10]).
-
Synchronize
- In this document, "to synchronize" refers to the
time-coordination of two or more presentation components (e.g., in a multimedia
presentation, a visual
track with captions). For Web content developers, the requirement to
synchronize means to provide the data that will permit sensible
time-coordinated rendering by a user agent. For example, Web content developers
can ensure that the segments of caption text are neither too long nor too
short, and that they map to segments of the visual track that are appropriate
in length. For user agent developers, the requirement to synchronize means to
present the content in a sensible time-coordinated fashion under a wide range
of circumstances including technology constraints (e.g., small text-only
displays), user limitations (slow reading speeds, large font sizes, high need
for review or repeat functions), and content that is sub-optimal in terms of
accessibility.
- Text
- In this document, the term "text" used by itself refers to
a sequence of characters from a markup language's document character set. Refer to the "Character
Model for the World Wide Web " [CHARMOD] for more information
about text and characters. Note: This document makes use of
other terms that include the word "text" that have highly specialized meanings:
collated text transcript, non-text content,
text content, non-text
element, text
element, text
equivalent, and text
transcript.
-
Text content, non-text content, text
element, non-text element, text equivalent non-text
equivalent
- As used in this document a "text element" adds text characters to either content or the
user interface. Both in the Web Content Accessibility Guidelines 1.0
[WCAG10] and in this document, text elements are presumed to produce
text that can be understood when rendered visually, as synthesized speech, or
as Braille. Such text elements benefit at least these three groups of users:
- visually-displayed text benefits users who are deaf and adept in reading
visually-displayed text;
- synthesized speech benefits users who are blind and adept in use of
synthesized speech;
- braille benefits users who are blind, and possibly deaf-blind, and adept at
reading braille.
A text element may consist of both text and non-text data. For instance, a
text element may contain markup for style (e.g., font size or color), structure
(e.g., heading levels), and other semantics. The essential function of the text
element should be retained even if style information happens to be lost in
rendering.
A user agent may have to process a text element in order to have access to
the text characters. For instance, a text element may consist of markup, it may
be encrypted or compressed, or it may include embedded text in a binary format
(e.g., JPEG).
"Text content" is content that is composed of one or more text elements. A
"text equivalent" (whether in content or the user interface) is an
equivalent composed of one or more text elements. Authors generally
provide text equivalents for content by using the
conditional content mechanisms of a specification.
A "non-text element" is an element (in content or the user interface) that
does not have the qualities of a text element. "Non-text content" is composed
of one or more non-text elements. A "non-text equivalent" (whether in content
or the user interface) is an
equivalent composed of one or more non-text elements.
Note that the terms "text element" and "non-text element" are defined by the
characteristics of their output (e.g., rendering) rather than those of their
input (e.g., information sources) or their internals (e.g., format). Both text
elements and non-text elements should be understood as "pre-rendering" content
in contrast to the "post-rendering" content that they produce.
-
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 pre-written
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:
- 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.
- The subject of a conformance claim to this document.
This is the most common use of the term in this document and is the usage in
the checkpoints.
- User agent default styles
- User agent default styles are style property values applied in the absence of
any author or user styles. Some markup languages specify a default rendering
for documents in that markup language. Other specifications may not specify
default styles. For example, XML 1.0 [XML]
does not specify default styles for XML documents. HTML 4
[HTML4] does not specify default styles for HTML documents, but the
CSS 2
[CSS2] specification suggests a sample default
style sheet for HTML 4 based on current practice.
-
User interface
- For the purposes of this document, user interface includes
both:
- the "user agent user
interface", i.e., the controls (e.g., menus, buttons, prompts,
etc.) 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 elements, links, applets,
etc.
The document distinguishes them only where required for clarity.
-
User styles
- User styles are style property values that come from user
interface settings, user style sheets, or other user interactions.
-
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. A visual track may be text-based or graphic. A visual track may be
static or involve
animation.
-
Views,
viewports
- The user agent renders content through one or more viewports.
Viewports include windows, frames, pieces of paper, loudspeakers, virtual
magnifying glasses, etc. A viewport may contain another viewport (e.g., nested
frames). User interface controls such as prompts, menus, alerts, etc. are not
viewports.
When the dimensions (spatial or temporal) of rendered content exceed the
dimensions of the viewport (e.g., when the user can only view a portion of a
large document through a small graphical viewport, when audio content has
already been played, etc.), 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.
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.
-
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].