Background

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.

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").

Hyphens are used to add additional descriptors to the end of terms. These descriptors are only added to clarify certain ambiguities with terms and only one descriptor is allowed at the end of any given term. For example, languages like MathML and latex are typically associated with encoding math content but are sometimes used to encode chemical equations and formulas. To ensure users can differentiate when these languages are being used for chemistry, the "-chemistry" descriptor is defined in this vocabulary for use on the respective math terms.

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").

If a user agent does not recognize a term with a descriptor, it should remove the hyphenated descriptor and attempt to process the base term.

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).

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

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

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:

• Structure and navigation terms identify navigation aids that are provided to simplify moving around within the media, such as the inclusion of a table of contents or an index.
• Adaptation terms identify content features that provide alternate access to a resource. The inclusion of alternative text in an [[HTML]] alt attribute is one of the most commonly identifiable augmentation features.
• Rendering control terms identify content rendering features that users have access to or can control. The ability to modify the appearance of the text is one example.
• Specialized markup terms identify that content is encoded using domain-specific grammars like MathML and ChemML that can provide users a richer reading experience.
• Clarity terms identify ways that the content has been enhanced for clearer readability. Audio with minimized background noise is one example, while content formatted for large print reading is another.
• Tactile terms identify content that is formatted for tactile use, such as graphics and objects.
• Internationalization terms identify those accessibility characteristics of the content which are required for internationalization.

The vocabulary also includes the term "none" that authors can set to indicate that the resource does not contain special enhancements. Similarly, the term "unknown" exists as a placeholder for marking content that authors need to review.

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

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.

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.

The accessibilityHazard property currently allows three types of hazards to be identified: flashing, motion simulation, and sound. These correspond to the values flashing, motionSimulation, and sound.

It also allows authors to indicate that each of the hazards is not present. In this case, the values follow the pattern "no…Hazard", using the hazard names in place of the ellipsis (e.g., noFlashingHazard).

If the author is sure there are no hazards, they are recommended to use the value "none" in place of specifying that each individual hazard is not present. When setting this value, no other hazard statuses are allowed.

Authors can additionally indicate that they are unable to determine if a hazard is present. In this case, the values follow the pattern "unknown…Hazard", using the hazard names in place of the ellipsis (e.g., unknownSoundHazard).

Authors can set the value unknown if they are unsure whether any hazards are present (e.g., because they do not know how, or are unable, to assess them). When setting this value, no other hazard statuses are allowed.

Vocabulary

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.

Vocabulary

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 resource 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

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" />
   <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>