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 Final Specification Agreement (FSA). 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 Final Specification Agreement (FSA) 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 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.
Indicates the resource is compatible with the iAccessible2 API [IAccessible2] for Windows.
Authors should use the NSAccessibility value instead.
Indicates the resource is compatible with the Java Accessibility API [JAPI].
Authors should use the 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
").
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.