This document defines the recommended vocabularies for use with the Schema.org accessibility properties for discoverability of creative works.

Introduction

Background

The CreativeWork type [[schema-org]] includes the following accessibility properties for discoverability:

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.

Vocabulary Naming Convention

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.

Extending the Vocabulary

To extend terms with more information, this vocabulary used to recommend 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.

Authors are no longer recommended to use this extension mechanism, although the use of slashes is not formally deprecated for backwards compatibility with existing content. The slash syntax was poorly defined, especially when multiple refinements could be specified, making it difficult for machines to process.

When a user may require more information about the characteristics of a resource (e.g., the specifics of what type of braille it contains), it is better to explain these in human-readable terms in an accessibility summary.

If a term in this vocabulary is not be expressive enough, it is now recommended to open an issue in the tracker to consider how to improve the existing term (e.g., by renaming terms or defining more specialized cases).

The accessibilityAPI Property

Application

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.

The expected value of the accessibilityAPI property is a list of the compatible APIs. For metadata formats incapable of expressing lists, the property should be repeated for each API.

Vocabulary

AndroidAccessibility

Indicates the resource is compatible with the Android Access API.

ARIA (deprecated)

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.

ATK

Indicates the resource is compatible with the Accessibility Toolkit (ATK) API [[ATK]] for GNOME.

AT-SPI

Indicates the resource is compatible with the Assistive Technology Service Provider Interface (AT-SPI) API [[AT-SPI]] for GNOME.

BlackberryAccessibility (obsolete)

Indicates the resource is compatible with the BlackBerry Accessibility API.

This value is now obsolete as BlackBerry devices phones and operating systems are no longer developed, sold, or maintained.

After 2016, the BlackBerry name was licensed for phones released using the Android platform. Compatibility with these devices must be indicated using the AndroidAccessibility value.

iAccessible2

Indicates the resource is compatible with the iAccessible2 API [[IAccessible2]] for Windows.

iOSAccessibility (deprecated)

Authors should use the NSAccessibility value instead.

JavaAccessibility

Indicates the resource is compatible with the Java Accessibility API [[JAPI]].

MacOSXAccessibility (deprecated)

Authors should use the UIAccessibility value instead.

MSAA

Indicates the resource is compatible with the Microsoft Active Accessibility (MSAA) API [[MSAA]] for Windows.

NSAccessibility

Indicates the resource is compatible with the NSAccessibility API for Apple iOS and tvOS applications built on UIKit.

UIAccessibility

Indicates the resource is compatible with the UIAccessibility API for macOS applications built on AppKit.

UIAutomation

Indicates the resource is compatible with the User Interface Automation API for Windows.

The accessibilityControl Property

Application

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.

The expected value of the accessibilityControl property is a list of the applicable control methods. For metadata formats incapable of expressing lists, the property should be repeated for each control method.

Vocabulary

fullKeyboardControl

Users can fully control the resource through keyboard input.

fullMouseControl

Users can fully control the resource through mouse input.

fullSwitchControl

Users can fully control the resource through switch input.

fullTouchControl

Users can fully control the resource through touch input.

fullVideoControl

Users can fully control the resource through video input.

fullVoiceControl

Users can fully control the resource through voice input.

The accessibilityFeature Property

Application

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:

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 expected value of the accessibilityFeature property is a list of the applicable features. For metadata formats incapable of expressing lists, the property should be repeated for each feature.

Vocabulary

Structure and Navigation Terms

The structure and navigation term identify structuring and navigation aids that facilitate use of the work.

annotations

The work includes annotations from the author, instructor and/or others.

ARIA

Indicates the resource includes ARIA roles to organize and improve the structure and navigation.

The use of this value corresponds to the inclusion of Document Structure, Landmark, Live Region, and Window roles [[WAI-ARIA]].

The accessibilityControl property can be used to indicate what input devices custom controls are accessible with.

bookmarks (deprecated)

The work includes bookmarks to facilitate navigation to key points.

The use of the bookmarks value is now deprecated due to its ambiguity. For PDF bookmarks, the tableOfContents value should be used instead. For bookmarks in ebooks, the annotations value can be used.

index

The work includes an index to the content.

printPageNumbers

The work includes equivalent print page numbers. This setting is most commonly used with ebooks for which there is a print equivalent.

readingOrder

The reading order of the content is clearly defined in the markup (e.g., figures, sidebars and other secondary content has been marked up to allow it to be skipped automatically and/or manually escaped from.

structuralNavigation

The use of headings in the work fully and accurately reflects the document hierarchy, allowing navigation by assistive technologies.

tableOfContents

The work includes a table of contents that provides links to the major sections of the content.

taggedPDF

The contents of the PDF have been tagged to permit access by assistive technologies.

Adaptation Terms

The adaptation terms identify provisions in the content that enable reading in alternative access modes.

alternativeText

Alternative text is provided for visual content (e.g., via the [[HTML]] alt attribute).

audioDescription

Audio descriptions are available (e.g., via an [[HTML]] track element with its kind attribute set to "descriptions").

captions

Indicates that synchronized captions are available for audio and video content.

describedMath

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.

longDescription

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).

rubyAnnotations

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.

signLanguage

Sign language interpretation is available for audio and video content.

Information about the sign language code used should be provided in the accessibility summary.

transcript

Indicates that a transcript of the audio content is available.

Rendering Control Terms

The rendering control values identify that access to a resource and rendering and playback of its content can be controlled for easier reading.

displayTransformability

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.

synchronizedAudioText

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.

timingControl

For content with timed interaction, this value indicates that the user can control the timing to meet their needs (e.g., pause and reset)

unlocked

No digital rights management or other content restriction protocols have been applied to the resource.

Specialized Markup Terms

The specialized markup terms identify content available in specialized markup grammars. These grammars typically provide users with enhanced structure and navigation capabilities.

ChemML

Identifies that chemical information is encoded using the ChemML markup language.

latex

Identifies that mathematical equations and formulas are encoded in the LaTeX typesetting system.

MathML

Identifies that mathematical equations and formulas are encoded in [[MathML]].

ttsMarkup

One or more of [[SSML]], [[Pronunciation-Lexicon]], and [[CSS3-Speech]] properties has been used to enhance text-to-speech playback quality.

Clarity Terms

The clarity terms identify ways that the content has been enhanced for improved auditory or visual clarity.

highContrastAudio

Audio content with speech in the foreground meets the contrast thresholds set out in WCAG Success Criteria 1.4.7.

Information about the how the audio meets the requirement should be provided in the accessibility summary (i.e., there is no background noise, at least 20db difference between foreground speech and background noise, or the background noise can be turned off.)

highContrastDisplay

Content meets the visual contrast threshold set out in WCAG Success Criteria 1.4.6.

largePrint

The content has been formatted to meet large print guidelines.

The property is not set if the font size can be increased. See displayTransformability.

Information about the type of large print (e.g., the font size) should be provided in the accessibility summary.

Tactile Terms

The tactile terms identify content that is available in tactile form.

braille

The content is in braille format, or alternatives are available in braille.

Information about the type of braille (e.g., ASCII, unicode, nemeth), whether the braille is contracted or not, and what code the braille conforms to should be provided in the accessibility summary.

tactileGraphic

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.

tactileObject

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.

none

Indicates that the resource does not contain any accessibility features.

The none value must not be set with any other feature value.

The accessibilityHazard Property

Application

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).

The expected value of the accessibilityHazard property is a list of the applicable hazards. For metadata formats incapable of expressing lists, the property should be repeated for each hazard.

Vocabulary

flashing

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]].

The flashing value must not be set when any of the noFlashingHazard, none, or unknown values are set.

noFlashingHazard

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]].

The noFlashingHazard value must not be set when either of the flashing or unknown values is set. It should not be set when the none value is set.

motionSimulation

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.

The motionSimulation value must not be set when any of the noMotionSimulationHazard, none, or unknown values are set.

noMotionSimulationHazard

Indicates that the resource does not contain instances of motion simulation.

The noMotionSimulation value must not be set when either of the motionSimulation or unknown values is set. It should not be set when the none value is set.

sound

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.

The sound value must not be set when any of the noSoundHazard, none, or unknown values are set.

noSoundHazard

Indicates that the resource does not contain auditory hazards.

The application of this value is currently under discussion as its application is underspecified.

The noSoundHazard value must not be set when either of the sound or unknown values is set. It should not be set when the none value is set.

unknown

Indicates that the author is not able to determine if the resource presents any hazards.

The unknown value must not be set with any other hazard value.

none

Indicates that the resource does not contain any hazards.

The none value must not be set when specifying either a known hazard or the unknown value. It should not be set when negative hazard claims are made.

The accessibilitySummary Property

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 accessMode Property

Application

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, where information is defined as any content that contributes to the understanding of the resource.

The expected value of the accessMode property is a list of the applicable access modes. For metadata formats incapable of expressing lists, the property should be repeated for each access mode.

The access modes do 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 be sufficient 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.

Vocabulary

auditory

Indicates that the resource contains information encoded in auditory form.

This value is not set when the auditory content conveys no information. For example, an instructional video might include background music while all the necessary information to complete the task is conveyed visually and/or through text captions.

chartOnVisual

Indicates that the resource contains charts encoded in visual form.

chemOnVisual

Indicates that the resource contains chemical equations encoded in visual form.

colorDependent

Indicates that the resource contains information encoded such that color perception is necessary.

diagramOnVisual

Indicates that the resource contains diagrams encoded in visual form.

mathOnVisual

Indicates that the resource contains mathematical notations encoded in visual form.

musicOnVisual

Indicates that the resource contains musical notation encoded in visual form.

tactile

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.

textOnVisual

Indicates that the resource contains text encoded in visual form.

textual

Indicates that the resource contains information encoded in textual form.

This value is not set if the only textual content is for navigational purposes. For example, an audiobook might include a table of contents, but it is not necessary to read the table of contents to read the work. Likewise, books with synchronized text-audio playback may only include headings to allow structured navigation.

visual

Indicates that the resource contains information encoded in visual form.

This value is not set if the only visual imagery is presentational or not directly relevant to understanding the content. Examples of this type of imagery include cover images for publications, corporate logos, and purely decorative images.

The accessModeSufficient property

Application

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 (e.g., through text-to-speech playback).

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.

Although listing the combinations of access modes that allow a user to read all the content is helpful, the most important sufficient access modes to list are the single-value ones. Users looking for an alternative to the default encoding of the content typically are looking for a single presentation mode (e.g., a fully textual pathway to use with a text-to-speech renderer or a fully auditory pathway to listen to).

The expected value of the accessModeSufficient property is an ItemList. Each entry in the ItemList must be a list of one or more access modes representing one pathway.

For formats incapable of expressing lists, the property should be repeated for each set of sufficient access modes. In these cases, it is recommended to use a comma-separated list of values.

Vocabulary

auditory

Indicates that auditory perception is necessary to consume the information.

tactile

Indicates that tactile perception is necessary to consume the information.

textual

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.

visual

Indicates that visual perception is necessary to consume the information.

Examples

Book

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>

Video

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>

Change Log

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.

Changes made in 2022

Acknowledgments

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 go to the original participants of the Accessibility Metadata Project for their work bringing the properties and vocabularies to reality.