- 1 Vocabulary
- 2 accessibilityFeature in detail
- 3 Example Markup
- 4 Issues Tracker and Open Issues
- 5 Discussion and Related Work
This page outlines the version 1.0 properties that are now part of schema.org. Work on the project is ongoing, and additional properties are being considered post 1.0. See the a11ymetadata.org web site for information on how to get involved.
(Note: Many of these values were derived from the IMS Global Access for All (AfA) Information Model Data Element Specification, and there is more information there on some terms.)
Accessibility terms (Version 1.0)
|Property||Expected Type||Expected Values||Description|
|| Content features of the resource, such as accessible media, supported enhancements for accessibility and alternatives.
See the accessibilityFeature in detail section below for more information.
|| A characteristic of the described resource that is physiologically dangerous to some users. Related to WCAG 2.0 guideline 2.3.
All three of the negative properties should be set if none of the hazards are known to exist. If the content has hazard(s), include positive assertions for the hazards it has and negative assertions for the others.
If the property is not set in the positive or negative or is specifically set to unknown, the state of hazards is not known.
||Indicates that the resource is compatible with the referenced accessibility API.|
||Identifies one or more input methods that allow access to all of the application functionality.|
accessibilityFeature in detail
The accessibilityFeature property supports many different values, and when alphabetized many of them will appear to have only tenuous relation. This section breaks the values out into their constituent groups to explain their inclusion.
There are four groups of features to be aware of:
- Transform features identify characteristics of the content that can be manipulated by the user to make the content better fit their personal needs. The ability to change the font size of the text is one example of a transformation property.
- Structure and navigation features 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.
- Control features identify content and features that are fully controllable by the user. The ability to pause a timed interface is an example.
- Augmentation features identify content features that provide alternate access to a resource. The inclusion of alternative text in an alt attribute is one of the most commonly identifiable augmentation features.
Each of the following section examines one of these classes values in more detail, listing the values and describing their expected use.
The property also includes the value "none" that can be set to indicate that the page has been checked but contains no special enhancements. The value can also be used to indicate that no statement about the accessibile nature of the content can be made. Setting this value helps differentiate pages that have been evaluated for accessibility from those that have not (i.e., to remove ambiguity about why the accessibilityFeature property might not have been set).
Features for transformation
Transform features either state how content is available in a transformed state or is set up so that a user can transform it. These properties derive from WCAG 2.0 section 1.4
| Audio content with speech in the foreground meets the contrast thresholds set out in WCAG Success Criteria 1.4.7. The success criterion the audio meets can be appeneded, but is not required:
|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.
| 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:
Note that many CSS display properties can be modified, but not all usefully enhance the accessibility (e.g., image-based content).
The following values identify key navigation aids available with the work.
|The work includes annotations from the author, instructor and/or others.|
|The work includes bookmarks to facilitate navigation to key points.|
|The work includes an index to the content.|
|The work includes equivalent print page numbers. This setting is most commonly used with ebooks for which there is a print equivalent.|
|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.|
|The use of headings in the work fully and accurately reflects the document hierarchy, allowing navigation by assistive technologies.|
|The structures in a PDF have been tagged to improve the navigation of the content.|
Features for content control
The following values identify aspects of the content that users can control to improve access to the content. Do not confuse these control features with the accessibilityControl property, which defines input methods used to control the 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 has the ability to 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.|
Features for augmentation
Augmentation is the provision of intellectual content in a different access mode from its source.
|Alternative text is provided for visual content (e.g., via the HTML alt attribute).|
|Audio descriptions are available (e.g., via the HTML5 track element).|
|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.|
|Indicates that synchronized captions are available for audio and video content.|
|Identifies that chemical information is encoded using the ChemML markup language.|
|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.|
|Identifies that mathematical equations and formulas are encoded using the designated markup language.|
|Descriptions are provided for image-based visual content and/or complex structures such as tables, mathematics, diagrams and charts.|
|Indicates that ruby annotations 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 ruby/annotations/* implies that no CJK ideographic characters have ruby.|
|Synchronized sign language intepretation 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.|
|Tactile graphics are provided. For example, as described in the BANA Guidelines and Standards for Tactile Graphics.|
|The content is a tactile 3D object, or the model to generate one is included.|
|Indicates that a transcript of the audio content is available.|
|One or more of SSML, PLS lexicons and CSS3 Speech properties has been used to enhance text-to-speech playback quality.|
Example 1 (Book)
The following example shows how the accessibility metadata is used to enhance Bookshare records. A description of the process of adding this metadata, and a corpus of searchable books, can be found at the accessibility metadata website.
<div itemscope="" itemtype="http://schema.org/Book">
<meta itemprop="bookFormat" content="EBook/DAISY3"/>
<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="noFlashingHazard"/>
<meta itemprop="accessibilityHazard" content="noMotionSimulationHazard"/>
<meta itemprop="accessibilityHazard" content="noSoundHazard"/>
<meta itemprop="accessibilityAPI" content="ARIA"/>
<dd itemprop="name">Holt Physical Science</dd>
<dd itemprop="description">NIMAC-sourced textbook</dd>
<dd itemprop="numberOfPages">598 Pages</dd>
<dd itemprop="publisher" itemtype="http://schema.org/Organization" itemscope="">Holt, Rinehart and Winston</dd>
<dt>Date of Addition:</dt>
<dd itemprop="copyrightHolder" itemtype="http://schema.org/Organization" itemscope="">Holt, Rinehart and Winston</dd>
<dd><meta itemprop="isFamilyFriendly" content="true"/>No</dd>
<dd><meta itemprop="inLanguage" content="en-US"/>English US</dd>
<dd><span itemprop="genre">Educational Materials</span></dd>
<dd>Sixth grade, Seventh grade, Eighth grade</dd>
<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>
<div class="bookReviews" itemprop="aggregateRating" itemscope itemtype="http://schema.org/AggregateRating">
<h2>Reviews of Holt Physical Science (<span itemprop="reviewCount">0</span> reviews)</h2>
<span><span itemprop="ratingValue>0</span> - No Rating Yet</span>
(The source record can be found at https://www.bookshare.org/browse/book/190639.)
Example 2 (Video)
This example shows how the accessibility metadata can be used to augment a record for a video.
<dl itemtype="http://schema.org/VideoObject" itemscope="">
<dd itemprop="name">Arctic Climate Perspectives</dd>
<dd itemprop="description">This video, adapted from material provided by the ECHO partners,
describes how global climate change is affecting Barrow, Alaska.</dd>
<!-- note that the spans in the next line are not in the immediate proposal -->
<dd><a itemprop="url" href="http://www.teachersdomain.org/asset/echo07_vid_climate">http://www.teachersdomain.org/asset/echo07_vid_climate</a>/</dd>
<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>
<dd>Grade 6, Grade 7, Grade 8, Grade 9</dd>
<dd><span itemprop="genre">Audio/Visual</span>, <span itemprop="genre">Movie/Animation</span></dd>
<dd>Download and Share, <a itemprop="useRightsUrl" href="http://www.teachersdomain.org/oerlicense/2/">http://www.teachersdomain.org/oerlicense/2/</a></dd>
Note that access modes are listed in the description, but do not have accesssibility metadata tags added. This property is not in the 1.0 specification, but is under consideration for 1.1. The adaptation URL is also not tagged as tagging for it is also still under discussion.
Issues Tracker and Open Issues
Discussion and Related Work
- Discussion List Google Group discussion list
- Accessibility Metadata Project primary site, including blog
- Additional Examples
- Live Examples: real marked up pages that can be searched
- A11yMetadata Crosswalk
- Additional long-form Resources for usage, especially
- Accessibility Metadata Semantic Markup Primer, which gives an overview of semantic tagging and how to apply these tags to content for accessibility
- Accessibility Metadata Best Practices Guide, which gives a longer description of the properties and their intended use than the one line in the specification
- Practical Property Guide, which gives guidance on the property use for the most common media and content types. Note that this has not been updated to the 1.0 specification, but the concepts of the accssibility features for each media type still hold. We'll update this if there is demand.
- IMS Global Access for All (AfA) Digital Resource Description (DRD) Version 3.0 Specification
- IMS Global Access For All (AfA) Digital Resource Description Specification Information Model
- Access for All XSD Schema Definition
- accessMode names are derived primarily from AfA AccessModeRequired.Type/existingAccessMode.
- mediaFeature names are derived primarily from AfA AdaptationTypeRequired.Type/adaptationRequest.
- IDPF.org guidelines discussing this work