Draft
Community
Group
Report
07
March
Copyright © 2022 the Contributors to the Schema.org Accessibility Properties for Discoverability Vocabulary Specification, published by the Accessibility Discoverability Vocabulary for Schema.org Community Group under the W3C Community Contributor License Agreement (CLA) . A human-readable summary is available.
This document defines the recommended vocabularies for use with the Schema.org accessibility properties for discoverability of creative works.
This specification was published by the Accessibility Discoverability Vocabulary for Schema.org Community Group . It is not a W3C Standard nor is it on the W3C Standards Track. Please note that under the W3C Community Contributor License Agreement (CLA) there is a limited opt-out and other conditions apply. Learn more about W3C Community and Business Groups .
GitHub Issues are preferred for discussion of this specification.
The
CreativeWork
type
[
schema-org
]
includes
the
following
accessibility
properties
for
discoverability:
accessibilityAPI
accessibilityControl
accessibilityFeature
accessibilityHazard
accessibilitySummary
accessMode
accessModeSufficient
Although schema.org contains many other properties that describe the accessibility of objects in its taxonomy, these specific properties were developed together as part of a project to improve the discoverability of accessible resources headed by Benetech and IMS Global. Many of these properties were derived directly from the IMS Global AccessForAll (AfA) Information Model Data Element Specification .
Part of this work included defining vocabularies of recommended values for use with these properties to ensure predictability for machine processing. This document represents those vocabularies.
By defining these vocabularies, not only is it simpler for authors to understand and apply the properties, but it ensures that search tools, user agents and other machine intelligence can easily parse and inform users of the information.
The vocabulary defined in this document is a continuation of the work that was informally hosted on the WebSchemas wiki (sometimes referred to as the "version 2.0 accessibility properties"). The project was moved to a W3C Community Group to better formalize the document and increase the transparency of its update process.
For more information about the original project, refer to the Accessibility Metadata Project's web site .
For more information on how to use schema.org accessibility properties not covered by this vocabulary, please refer to their relevant definitions in schema.org.
The values defined in this vocabulary follow a camel casing convention: single words are lowercase, while compound words are concatenated into a single value with a capital letter indicating the start of each connected word (e.g., "alternativeText"). This convention is not applied to acronyms, accessibility APIs, and other values that already have recognized naming conventions (e.g., "MathML" and "iOSAccessibility").
To ensure maximum interoperability with user agents that process these properties, use the values exactly as they are defined in this vocabulary. Alternative case spellings may not be recognized (e.g., "mathml" or "aria").
User agent developers should be aware that these values may not be strictly validated depending on the context in which they are created and used. Two values that differ only in case should be treated as identical.
This
vocabulary
currently
uses
the
old
slash
extension
syntax
employed
by
Schema.org
until
2015.
In
this
model,
extensions
of
a
term
are
made
by
adding
a
slash
followed
by
a
refinement
term.
For
example,
see
the
braille
feature
for
specifying
specific
braille
codes.
Authors are advised to use this extension mechanism sparingly at this time, as a future version of the vocabulary may update this approach.
Indicates that the resource is compatible with the referenced accessibility API.
Compatibility with an accessibility API indicates that assistive technologies on the platform should be able to access the resource.
The property is not applicable to resources that are not tightly integrated with their user interface. It can describe whether a word processing document that only opens in a specific application will work on a given platform, for example, but is not a useful indicator of whether an HTML document will, as there are numerous user agents a user could use to render it.
Setting the property means that the resource is compatible with the given API(s). It does not necessarily mean that the content will be fully accessible to any given user group.
Indicates
the
resource
is
compatible
with
the
Android
Accessibility
API.
Access
API
.
Indicates the resource uses ARIA [ WCAG21 ] markup to improve interoperability with platform APIs.
The
use
of
the
ARIA
value
is
now
deprecated
as
ARIA
is
not
an
accessibility
API.
The
accessibilityFeature
property
value
"
ARIA
"
is
now
recommended
to
use
to
indicate
that
a
resource
makes
use
of
ARIA
to
improve
structural
navigation.
Indicates the resource is compatible with the Accessibility Toolkit (ATK) API [ ATK ] for GNOME.
Indicates the resource is compatible with the Assistive Technology Service Provider Interface (AT-SPI) API [ AT-SPI ] for GNOME.
Indicates
the
resource
is
compatible
with
the
Blackberry
Accessibility
API.
API
.
Indicates the resource is compatible with the iAccessible2 API [ IAccessible2 ] for Windows.
Indicates
the
resource
is
compatible
with
Authors
should
use
the
iAccessible2
API
for
Apple
iOS
devices.
NSAccessibility
value
instead.
Indicates
the
resource
is
compatible
with
the
Java
Accessibility
API
(JAAPI).
[
JAPI
].
Indicates
the
resource
is
compatible
with
Authors
should
use
the
iAccessible2
API
for
Windows.
UIAccessibility
value
instead.
Indicates the resource is compatible with the Microsoft Active Accessibility (MSAA) API [ MSAA ] for Windows.
Indicates the resource is compatible with the NSAccessibility API for Apple iOS and tvOS applications built on UIKit.
Indicates the resource is compatible with the UIAccessibility API for macOS applications built on AppKit.
Indicates the resource is compatible with the User Interface Automation API for Windows.
Identifies one or more input methods that allow access to all of the application functionality.
The
accessibilityControl
property
is
used
to
describe
the
ability
of
users
to
interact
with
the
user
interface
controls
that
applications
provide.
The property is not applicable to resources that are not tightly integrated with their user interface. It can describe whether users can control a word processing document that only opens in a specific application, for example, but is not a useful indicator of whether users can control an HTML document, as there are numerous user agent and assistive technology pairings a user could use to access it.
Setting the property means that the specified control method(s) are compatible with the resource.
Users can fully control the resource through keyboard input.
Users can fully control the resource through mouse input.
Users can fully control the resource through switch input.
Users can fully control the resource through touch input.
Users can fully control the resource through video input.
Users can fully control the resource through voice input.
Content features of the resource, such as accessible media, alternatives and supported enhancements for accessibility.
The
accessibilityFeature
property
provides
a
list
of
all
the
applicable
accessibility
characteristics
of
the
content.
It
allows
a
user
agent
to
discover
these
characteristics
without
having
to
parse
or
interpret
the
structure
of
the
content.
For ease of reading, this section splits the vocabulary into the following distinct groups:
alt
attribute
is
one
of
the
most
commonly
identifiable
augmentation
features.
The
vocabulary
also
includes
the
term
"
none
"
that
authors
can
set
to
indicate
that
the
resource
does
not
contain
special
enhancements.
This
value
avoids
the
ambiguity
that
can
arise
if
a
resource
has
not
been
checked.
The adaptation terms identify provisions in the content that enable reading in alternative access modes.
Alternative
text
is
provided
for
visual
content
(e.g.,
via
the
[
HTML
]
alt
attribute
).
Audio
descriptions
are
available
(e.g.,
via
an
[
HTML
]
track
element
with
its
kind
attribute
set
to
"
descriptions
").
Indicates that synchronized captions are available for audio and video content.
Textual
descriptions
of
math
equations
are
included,
whether
in
the
alt
attribute
for
image-based
equations,
using
the
alttext
attribute
for
[
MathML
]
equations,
or
by
other
means.
Descriptions are provided for image-based visual content and/or complex structures such as tables, mathematics, diagrams, and charts.
Authors
may
set
this
property
independent
of
the
method
they
use
to
provide
the
extended
descriptions
(i.e.,
it
is
not
required
to
use
the
obsolete
[
HTML
]
longdesc
attribute
).
Indicates
that
ruby
annotations
[
HTML
]
are
provided
in
the
content.
Ruby
annotations
are
used
as
pronunciation
guides
for
the
logographic
characters
for
languages
like
Chinese
or
Japanese.
It
makes
difficult
Kanji
or
CJK
ideographic
characters
more
accessible.
The
absence
of
rubyAnnotations
implies
that
no
CJK
ideographic
characters
have
ruby.
Sign
language
interpretation
is
available
for
audio
and
video
content.
The
value
may
be
extended
by
adding
an
[
ISO-639
]
sign
language
code.
For
example,
/sgn-en-us
for
American
Sign
Language.
Indicates that a transcript of the audio content is available.
The rendering control values identify that access to a resource and rendering and playback of its content can be controlled for easier reading.
Display properties are controllable by the user. This property can be set, for example, if custom CSS style sheets can be applied to the content to control the appearance. It can also be used to indicate that styling in document formats like Word and PDF can be modified.
This property can be modified to identify the specific display properties that allow meaningful control. Modifiers should take the form of CSS property names, even if CSS is not the document styling format:
/font-size
/font-family
/line-height
/word-spacing
/color
/background-color
Note that many CSS display properties can be modified, but not all usefully enhance the accessibility (e.g., image-based content).
Describes a resource that offers both audio and text, with information that allows them to be rendered simultaneously. The granularity of the synchronization is not specified. This term is not recommended when the only material that is synchronized is the document headings.
For content with timed interaction, this value indicates that the user can control the timing to meet their needs (e.g., pause and reset)
No digital rights management or other content restriction protocols have been applied to the resource.
The specialized markup terms identify content available in specialized markup grammars. These grammars typically provide users with enhanced structure and navigation capabilities.
Identifies that chemical information is encoded using the ChemML markup language .
Identifies that mathematical equations and formulas are encoded in the LaTeX typesetting system .
Identifies that mathematical equations and formulas are encoded in [ MathML ].
One or more of [ SSML ], [ Pronunciation-Lexicon ], and [ CSS3-Speech ] properties has been used to enhance text-to-speech playback quality.
The clarity terms identify ways that the content has been enhanced for improved auditory or visual clarity.
Audio content with speech in the foreground meets the contrast thresholds set out in WCAG Success Criteria 1.4.7 . The requirement the audio meets can be appended, but is not required:
/noBackground
-
no
background
noise
is
present
/reducedBackground
-
at
least
20db
difference
between
foreground
speech
and
background
noise
/switchableBackground
-
background
noise
can
be
turned
off
(sufficient
contrast
may
not
be
met
without
doing
so)
Content meets the visual contrast threshold set out in WCAG Success Criteria 1.4.6 .
The
content
has
been
formatted
to
meet
large
print
guidelines.
The
specific
point
size
may
optionally
be
added
as
an
extension
(e.g.,
largePrint/18
).
The
property
is
not
set
if
the
font
size
can
be
increased.
See
displayTransformability
.
The tactile terms identify content that is available in tactile form.
The
content
is
in
braille
format,
or
alternatives
are
available
in
braille.
This
value
can
be
extended
to
identify
the
different
types
of
braille
(
/ASCII
,
/unicode
,
/music
,
/math
,
/chemistry
or
/nemeth
),
and
whether
the
braille
is
contracted
or
not
(
/grade1
and
/grade2
).
Other
extensions
such
as
the
code
the
braille
conforms
to
can
also
be
specified.
When used with creative works such as books, indicates that the resource includes tactile graphics.
When used to describe an image resource or physical object, indicates that the resource is a tactile graphic.
Refer to the BANA Guidelines and Standards for Tactile Graphics for more information about tactile graphic formats and formatting.
When used with creative works such as books, indicates that the resource includes models to generate tactile 3D objects.
When used to describe a physical object, indicates that the resource is a tactile 3D object.
Indicates that the resource does not contain any accessibility features.
A characteristic of the described resource that is physiologically dangerous to some users. Related to WCAG 2.0 guideline 2.3 .
Identifying potential hazards that a resource poses allows users to determine if a resource poses a risk to them and to potentially filter out content that could be harmful.
If
no
hazards
are
known
to
exist,
it
is
recommended
to
use
the
value
"
none
".
If
the
content
has
hazard(s),
include
positive
assertions
for
the
hazards
it
has
and
negative
assertions
(the
values
that
begin
with
"no")
for
the
others.
If
this
property
is
not
set
for
a
resource,
it
is
not
possible
to
state
whether
it
presents
hazards
or
not.
Similarly,
if
an
author
sets
the
value
unknown
,
they
are
stating
that
they
do
not
know
whether
hazards
are
present
(e.g.,
because
they
do
not
know
how,
or
are
unable,
to
assess
them).
Indicates that the resource presents a flashing hazard for photosensitive persons.
This value should be set when the content meets the hazard thresholds described in Success Criterion 2.3.1 Three Flashes or Below Threshold [ WCAG2 ].
Indicates that the resource does not present a flashing hazard.
This value should be set when the content conforms to Success Criterion 2.3.1 Three Flashes or Below Threshold [ WCAG2 ].
Indicates that the resource contains instances of motion simulation that may affect some individuals.
Some examples of motion simulation include video games with a first-person perspective and CSS-controlled backgrounds that move when a user scrolls a page.
Indicates that the resource does not contain instances of motion simulation.
Indicates that the resource contains auditory sounds that may affect some individuals.
The application of this value is currently under discussion as its application is underspecified.
Indicates that the resource does not contain auditory hazards.
The application of this value is currently under discussion as its application is underspecified.
Indicates that the author is not able to determine if the resource presents any hazards.
Indicates that the resource does not contain any hazards.
A human-readable summary of specific accessibility features or deficiencies, consistent with the other accessibility metadata but expressing subtleties such as "short descriptions are present but long descriptions will be needed for non-visual users" or "short descriptions are present and no long descriptions are needed."
The
accessibilitySummary
property
is
a
free-form
field
that
allows
authors
to
describe
the
accessible
properties
of
the
resource.
As
a
result,
it
does
not
have
an
associated
vocabulary.
The human sensory perceptual system or cognitive faculty through which a person may process or perceive information.
The
accessMode
property
describes
the
ways
information
is
encoded
in
the
resource,
but
it
does
not
tell
users
if
all
the
specified
modes
are
necessary
to
consume
the
information
or
if
only
individual
modes
or
combinations
are
necessary
(e.g.,
in
a
book
with
audio
content,
the
ability
to
read
textual
content
may
only
be
necessary
if
transcripts
are
provided).
The
accessModeSufficient
property
is
designed
to
fill
this
gap
of
understanding
the
combinations
of
modes
necessary
to
fully
consume
the
information.
Indicates that the resource contains information encoded in auditory form.
Indicates that the resource contains charts encoded in visual form.
Indicates that the resource contains chemical equations encoded in visual form.
Indicates that the resource contains information encoded in such that color perception is necessary.
Indicates that the resource contains diagrams encoded in visual form.
Indicates that the resource contains mathematical notations encoded in visual form.
Indicates that the resource contains musical notation encoded in visual form.
Indicates that the resource contains information encoded in tactile form.
Note that although an indication of a tactile mode often indicates the content is encoded using a braille system, this is not always the case. Tactile perception may also indicate, for example, the use of tactile graphics to convey information.
Indicates that the resource contains text encoded in visual form.
Indicates that the resource contains information encoded in textual form.
Indicates that the resource contains information encoded in visual form.
A list of single or combined accessModes that are sufficient to understand all the intellectual content of a resource.
Although the access modes indicate how the information is encoded in its default form, knowing the encoding only describes one possible perceptual pathway through the content. For example, a book with textual and visual content will, at the most basic level, require an individual who can read text and view images.
The author of the content may, however, provide alternatives to a specific access mode that allow the content to be wholly consumed in another manner. The use of alternative text and extended descriptions, for example, can allow a user who cannot perceive visual content to read all the information in textual form.
In
such
a
case,
a
work
with
textual
and
visual
access
modes
could
have
both
a
textual
and
visual
sufficient
access
mode
and
a
purely
textual
access
mode
—
because
there
are
text
equivalents
for
the
visual
content.
Specifying
there
is
an
additional
textual-only
pathway
through
the
content
allows
users
of
screen
readers,
for
example,
to
recognize
that
the
content
will
be
readable
by
them.
It is for this reason that content that has multiple access modes may have one or more sets of sufficient access modes: each listing of sufficient access modes provides users with one possible combination of reading modes that allow the content to be read in full.
Indicates that auditory perception is necessary to consume the information.
Indicates that tactile perception is necessary to consume the information.
Indicates that the ability to read textual content is necessary to consume the information.
Note that reading textual content does not require visual perception, as textual content can be rendered as audio using a text-to-speech capable device or assistive technology.
Indicates that visual perception is necessary to consume the information.
The following example shows how accessibility metadata could be used to enhance a library record available on the Web.
<div itemscope="" itemtype="http://schema.org/Book">
<meta itemprop="bookFormat" content="EBook/DAISY3" />
<meta itemprop="accessibilityFeature" content="ARIA" />
<meta itemprop="accessibilityFeature" content="largePrint" />
<meta itemprop="accessibilityFeature" content="highContrastDisplay" />
<meta itemprop="accessibilityFeature" content="displayTransformability/resizeText" />
<meta itemprop="accessibilityFeature" content="longDescription" />
<meta itemprop="accessibilityFeature" content="alternativeText" />
<meta itemprop="accessibilityFeature" content="readingOrder" />
<meta itemprop="accessibilityFeature" content="structuralNavigation" />
<meta itemprop="accessibilityFeature" content="tableOfContents" />
<meta itemprop="accessibilityControl" content="fullKeyboardControl" />
<meta itemprop="accessibilityControl" content="fullMouseControl" />
<meta itemprop="accessibilityHazard" content="none" />
<dl>
<dt>Name:</dt>
<dd itemprop="name">Holt Physical Science</dd>
<dt>Brief Synopsis:</dt>
<dd itemprop="description">NIMAC-sourced textbook</dd>
<dt>Long Synopsis:</dt>
<dd>N/A</dd>
<dt>Book Quality:</dt>
<dd>Publisher Quality</dd>
<dt>Book Size:</dt>
<dd itemprop="numberOfPages">598 Pages</dd>
<dt>ISBN-13:</dt>
<dd itemprop="isbn">9780030426599</dd>
<dt>Publisher:</dt>
<dd itemprop="publisher" itemtype="http://schema.org/Organization" itemscope="">Holt, Rinehart
and Winston</dd>
<dt>Date of Addition:</dt>
<dd>06/08/10</dd>
<dt>Copyright Date:</dt>
<dd itemprop="copyrightYear">2007</dd>
<dt>Copyrighted By:</dt>
<dd itemprop="copyrightHolder" itemtype="http://schema.org/Organization" itemscope="">Holt,
Rinehart and Winston</dd>
<dt>Adult content:</dt>
<dd><meta itemprop="isFamilyFriendly" content="true" />No</dd>
<dt>Language:</dt>
<dd><meta itemprop="inLanguage" content="en-US" />English US</dd>
<dt>Essential Images:</dt>
<dd>861</dd>
<dt>Described Images:</dt>
<dd>910</dd>
<dt>Categories:</dt>
<dd><span itemprop="genre">Educational Materials</span></dd>
<dt>Grade Levels:</dt>
<dd>Sixth grade, Seventh grade, Eighth grade</dd>
<dt>NIMAC:</dt>
<dd>This book is currently only available to public K-12 schools and organizations in the United
States for use with students with an IEP, because it was created from files supplied by the
NIMAC under these restrictions. Learn more in the NIMAC Support Center.</dd>
</dl>
<div class="bookReviews" itemprop="aggregateRating" itemscope=""
itemtype="http://schema.org/AggregateRating">
<h2>Reviews of Holt Physical Science (<span itemprop="reviewCount">0</span> reviews)</h2>
<div class="bookReviewScore">
<span><span itemprop="ratingValue">0</span> - No Rating Yet</span>
</div>
</div>
</
div
>
This example shows how the accessibility metadata could be used to augment a record for a video.
<dl itemtype="http://schema.org/VideoObject" itemscope="">
<dt>Title:</dt>
<dd itemprop="name">Arctic Climate Perspectives</dd>
<dt>Description:</dt>
<dd itemprop="description">This video, adapted from material provided by the ECHO
partners, describes how global climate change is affecting Barrow, Alaska.</dd>
<dt>Adaptation Type:</dt>
<dd><span itemprop="accessibilityFeature">captions</span></dd>
<dt>Access Mode:</dt>
<dd>auditory, visual</dd>
<dt>URL:</dt>
<dd><a itemprop="url" href="http://www.example.org/asset/echo07_vid_climate"
>http://www.example.org/asset/echo07_vid_climate</a>/</dd>
<dt>Has Adaptation:</dt>
<dd>http://www.example.org/asset/echo07_vid_climate_dvs/</dd>
<dt>Subjects:</dt>
<dd><span itemprop="about">National K-12 Subject::Science::Earth and Space
Science::Water Cycle, Weather, and Climate::Structure and Composition of the
Atmosphere, National K-12 Subject::Science::Earth and Space Science::Water Cycle,
Weather, and Climate::Climate</span></dd>
<dt>Education Level:</dt>
<dd>Grade 6, Grade 7, Grade 8, Grade 9</dd>
<dt>Audience:</dt>
<dd><span itemprop="intendedEndUserRole">Learner</span></dd>
<dt>Resource Type:</dt>
<dd><span itemprop="genre">Audio/Visual</span>,
<span itemprop="genre">Movie/Animation</span></dd>
<dt>Language:</dt>
<dd><span itemprop="inLanguage">en-US</span></dd>
<dt>Publication Date:</dt>
<dd itemprop="datePublished">2007-02-12</dd>
<dt>Rights:</dt>
<dd>Download and Share, <a itemprop="useRightsUrl"
href="http://www.example.org/oerlicense/2/"
>http://www.example.org/oerlicense/2/</a></dd>
</
dl
>
Note
that
this
change
log
only
identifies
substantive
changes
to
the
vocabulary
—
those
that
add
or
deprecate
terms,
or
are
similarly
noteworthy.
For a list of all issues addressed (typos, minor definition modifications, etc.), refer to the Community Group's issue tracker .
accessibilityFeature
.
See
pull
request
39
.
accessibilityAPI
value
"ARIA"
is
deprecated.
It
is
replaced
by
a
new
"ARIA"
value
for
accessibilityFeature
for
indicating
the
use
of
roles
of
enhanced
structural
and
landmark
navigation.
See
issue
4
.
The editors would like to thank the Accessibility Discoverability Vocabulary for Schema.org Community Group participants for their ongoing input and suggestions to improve this vocabulary.
Additional thanks goes to the original participants of the Accessibility Metadata Project for their work bringing the properties and vocabularies to reality.