Introduction to Schema.org Accessibility Metadata
This resource defines all of the schema.org accessibility metadata properties and provides guidance on what to include in your OPF file.
The schema.org CreativeWork class includes a set of properties used to identify the accessible qualities of a publication. In this resource, we’ll take a close look at each one and talk about how to determine what should be included in your book’s metadata.
Schema.org Accessibility Properties
The properties (or you can think of them as categories) that should be used are:
- accessibilitySummary: Provides a human-readable overview of the accessibility of the text;
- accessibilityFeature: Shares the accessibility features that have been included;
- accessibilityHazard: Provides warnings for features that could be an issue for some readers;
- accessMode: Describes the contents of the book; and
- accessModeSufficient: Identifies the different combinations of senses that can be used to consume the content. This property is only “recommended,” not required, to meet the EPUB Accessibility Specification, but including it can be really helpful to a reader.
Accessibility Summary
The accessibilitySummary is a human-readable overview of accessibility features. There is one accessibilitySummary.
The Accessibility Summary Authoring Guidelines explain it quite well: “This piece of metadata is extraordinarily unique and important in that it provides a human-readable description of the accessibility of the publication. It is expected that people who do not have formal training in HTML, EPUB, or who are not experts in accessibility will be reading the accessibilitySummary.” They also provide some helpful high-level considerations:
- Use plain language;
- Avoid jargon;
- Write out acronyms before using the abbreviation; e.g., Web Content Accessibility Guidelines (WCAG);
- Include all accessibility features (AccessibilitySummary may be the only piece of metadata that some users read); and
- If you decide to use a template, make sure the AccessibilitySummary is customized for every book.
Example:
<meta property="schema:accessibilitySummary">This publication is screen-reader-friendly and is accessible to users of assistive technology. It was created with accessibility in mind. There are image descriptions, a page list, and detailed navigation/structure. There are no accessibility hazards like sound or video. It meets the Web Content Accessibility Guidelines (WCAG), Level “AA”.</meta>
accessibilityFeature
The accessibilityFeature property shares the features that you have worked to include in the ebook. You can include as many properties as you need. The following list covers the most common features you might include in an accessible book. It is non-exhaustive — to see all possible (and up-to-date) features, refer to the W3C’s “Schema.org Accessibility Properties for Discoverability Vocabulary” (see Links to More Information).
accessibilityFeature Values
| Feature | Description | Code for EPUB 3 |
| alternativeText | All important images include a text alternative description | <meta property="schema:accessibilityFeature">alternativeText</meta>
|
| displayTransformability | Users can modify the display of textual content such as font family and size | <meta property="schema:accessibilityFeature">displayTransformability</meta> |
| index | The publication contains an index of the content, such as a topical index | <meta property="schema:accessibilityFeature">index</meta> |
| longDescription | All complex images include an extended description of their purpose. | <meta property="schema:accessibilityFeature">longDescription</meta> |
| none | The publication does not include any accessibility features. If this is true for your book, mentioning it in the metadata is a great thing to do. | <meta property="schema:accessibilityFeature">none</meta> |
| printPageNumbers | Static print page break locations are included in the text | <meta property="schema:accessibilityFeature">printPageNumbers</meta> |
| readingOrder | There is a logical reading order to the text | <meta property="schema:accessibilityFeature">readingOrder</meta> |
| structuralNavigation | All headings are properly marked up | <meta property="schema:accessibilityFeature">structuralNavigation</meta> |
| synchronizedAudioText | Audio narration is available, and synchronizes with the text | <meta property="schema:accessibilityFeature">synchronizedAudioText</meta> |
| tableOfContents | There is a table of contents that links to major sections of the book. | <meta property="schema:accessibilityFeature">tableOfContents</meta> |
The accessibilityFeature property shares the features that you have worked to include in the ebook. You can include as many properties as you need. The following list covers the most common features you might include in an accessible book.
accessibilityHazard
The accessibilityHazard property discloses any features that may have an unwanted physiological impact on some readers.
This could include things such as flashing lights, which can cause seizures; motion simulation, which can cause motion sickness; or sound (certain sounds can also cause seizures).
The following list covers all current hazards you need to note in an accessible book. To see all possible (and up-to-date) features, refer to the W3C’s “Schema.org Accessibility Properties for Discoverability Vocabulary” (see Links to More Information).
accessibilityHazard Values
| Hazard | Description | Code for EPUB 3 |
flashing
| There is content that contains a flashing hazard for people with photosensitivity.
| <meta property="schema:accessibilityHazard">flashing</meta>
|
| noFlashingHazard | There is no flashing hazard. | <meta property="schema:accessibilityHazard">noFlashingHazard</meta> |
| motionSimulation | There is content that contains motion simulation. | <meta property="schema:accessibilityHazard">motionSimulation</meta> |
| noMotionSimulationHazard | There is no motion simulation. | <meta property="schema:accessibilityHazard">noMotionSimulationHazard</meta> |
| sound | The content has auditory sounds.
Note: To be on the safe side, this property should be included if a publication contains any audio content, and users should have the ability to choose whether or not to play the content. | <meta property="schema:accessibilityHazard">sound</meta> |
| noSoundHazard | There are no auditory hazards. | <meta property="schema:accessibilityHazard">noSoundHazard</meta> |
| unknown | Use this if you are unable to determine if any hazards are present. | <meta property="schema:accessibilityHazard">unknown</meta> |
| none | There are no hazards present. | <meta property="schema:accessibilityHazard">none</meta> |
accessibilityHazard discloses any features that may have an unwanted physiological impact on some readers. This could include things like flashing, which can cause seizures; motion simulation, which can cause motion sickness, or sound—certain sounds can also cause seizures. The following list covers all current hazards you need to note in an accessible book.
accessMode
The accessMode property is used to describe how people can perceive the information/content of a book.
More than one type of content can be included, with each mode on a different line. The following (non-exhaustive) list covers the most common modes you might include in an accessible book. To see all possible (and up-to-date) access modes, refer to the W3C’s “Schema.org Accessibility Properties for Discoverability Vocabulary” (see Links to More Information).
| Mode of access | Description | Code for EPUB 3 |
| textual | accessMode “textual” will be included for basically every ebook, ever! It means that the book has information that can be accessed “textually” – i.e., there is text in it that a person or a screen reader can access. | <meta property="schema:accessMode">textual</meta> |
| visual | accessMode “visual” means that the book contains images, graphics, or video. 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. | <meta property="schema:accessMode">visual</meta> |
| auditory | accessMode “auditory” means that the book contains audio - whether it is narration embedded in the text, songs you can play, or any other bit of audio, big or small. | <meta property="schema:accessMode">auditory</meta> |
| tactile | accessMode “tactile” means that the book contains tactile content, like tactile graphics or diagrams, or electronic braille. | <meta property="schema:accessMode">tactile</meta> |
accessModeSufficient
The accessModeSufficient property refers to the way that someone can access all of the content/information in a book. If the book has text and images, then we say “textual, visual” — i.e., someone can read the text and look at the images. If the book has included image descriptions, then we can also say “textual,” since everything in the book can be accessed through text (i.e., the image descriptions can be read). If the book has embedded audio that describes all images and narrates all text including front and back matter, then we can say “auditory.”
The following list covers all current “sufficient access modes” you need to note in an accessible book. To see all possible (and up-to-date) modes, refer to the W3C’s “Schema.org Accessibility Properties for Discoverability Vocabulary” (see Links to More Information).
accessModeSufficient Values
| Sufficient Access Mode | Description | Code for EPUB 3 |
| textual | accessModeSufficient “textual” can be included when all of the book's content can be accessed textually — usually this means that all images are described. | <meta property="schema:accessModeSufficient">textual</meta> |
| visual | accessModeSufficient “visual” can be included when all of the book's content can be accessed visually. This will apply to almost every book. | <meta property="schema:accessModeSufficient">visual</meta> |
| auditory | accessModeSufficient “auditory” can be included when all of the book's content can be accessed via included audio — all text and images are included in the recording | <meta property="schema:accessModeSufficient">auditory</meta> |
| tactile | accessModeSufficient “tactile” can be included when all of the book's content can be accessed via touch — usually this means that all images are described | <meta property="schema:accessModeSufficient">tactile</meta> |
| combinations | If the book has text and images, then we say “textual, visual” – i.e., someone can read the text and look at the images. If the book has included image descriptions, then we can also say “textual”, since everything in the book can be accessed through text (i.e., the image descriptions can be read). The example in the following cell is what will appear in most ebook OPF files if the book has text and images, and the images are described. | <meta property="schema:accessModeSufficient">textual, visual</meta> |
accessModeSufficient refers to the way that someone can access all of the content/information in a book. If the book has text and images, then we say “textual, visual” – i.e., someone can read the text and look at the images. If the book has included image descriptions, then we can also say “textual”, since everything in the book can be accessed through text (i.e., the image descriptions can be read). If the book has embedded audio that describes all images, and narrates all text including front and back matter, then we can say "auditory".
Example
Now that we have covered all of the Schema.org options, let’s look at an example.
Let’s say we have a reflowable novel with:
- Image descriptions;
- Long descriptions;
- A complete navigation file and heading structure;
- A table of contents; and
- Some audio clips.
Here is a set of Schema.org metadata we might include:
<meta property="schema:accessibilitySummary">This Publication meets the requirements of the EPUB Accessibility specification with conformance to WCAG 2.0 Level AA. The content is screen-reader friendly. Images are described, long descriptions have been included for complex images, a table of contents is present, and sections are introduced with correctly-cascading headings. There are short audio clips of music at the start of each chapter which readers can choose to play – they will not auto-play.</meta>
<meta property="schema:accessMode">textual</meta>
<meta property="schema:accessMode">visual</meta>
<meta property="schema:accessModeSufficient">textual,visual</meta>
<meta property="schema:accessModeSufficient">textual</meta>
<meta property="schema:accessibilityFeature">alternativeText</meta>
<meta property="schema:accessibilityFeature">longDescription</meta>
<meta property="schema:accessibilityFeature">structuralNavigation</meta>
<meta property="schema:accessibilityFeature">tableOfContents</meta>
<meta property="schema:accessibilityHazard">noFlashingHazard</meta>
<meta property="schema:accessibilityHazard">noMotionSimulationHazard</meta>
<meta property="schema:accessibilityHazard">sound</meta>
Next Steps
1
Adding Accessibility Metadata to an Ebook
Introduction to Accessibility Metadata for Ebooks
Accessibility metadata should be included with every ebook, as it lets the reader know about what accessibility features have been included! This introduction discusses the importance of accessibility metadata, and shares examples of each type.
Subject(s): Metadata
Resource Type(s): Standards and Best Practices
2
Creating Accessibility Metadata for an ONIX Record
Introduction to ONIX Metadata for Ebooks (and the Supply Chain)
This resource discusses the importance of ONIX accessibility metadata, and shares an example of the accessibility section of an ONIX file.
Subject(s): Metadata
Resource Type(s): Foundations and Rationale, Standards and Best Practices
External Links to More Information
Schema.org Accessibility Properties for Discoverability Vocabulary
This document discusses all Schema.org metadata, providing definitions, as well as lists of all of the possible properties and terms.
Metadata in Publishing — The Hidden Information Essential for Accessibility
This page has brief explanations of how to mark up several types of content including sections, headings, emphasis, figures, sidebars, and blockquotes among others. It also discusses ARIA roles for the included elements where applicable. The page ends with a discussion of accessibility metadata
Accessible Publishing Knowledge Base
This is an excellent reference with details and best practices for many EPUB accessibility topics. It provides explanations and code examples. Coverage includes EPUB accessibility, validation, metadata, HTML, and CSS from the perspective of using available markup elements to their full potential for accessibility.
European Accessibility Act requirements: are publishing standards as EPUB, ONIX and Schema.org fully compliant?
This page discusses the European accessibility requirements set to come into effect in 2025. Research was done to discover whether the existing metadata schemes of ONIX and schema.org metadata provide the needed information about the accessibility of ebooks. The results suggest that these do provide what is needed. A more detailed report is also available for download.
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