The EPUB Accessibility Metadata Guide details when to set the Schema.org accessibility metadata properties in the EPUB package document.
This guide only details usage for EPUB publications. The guidance in this document may not be relevant to other formats.
Schema.org [[schema-org]] is described as a collaborative, community activity with a mission to
create, maintain, and promote schemas for structured data.
Of particular importance is that it
includes the following set of accessibility properties for describing creative works:
These properties are key to the discoverability of EPUB publications and are central to the requirements of the EPUB Accessibility standard [[epub-a11y]]. They are also used to generate accessibility statements about a publication, as described in the Accessibility Metadata Display Guide for Digital Publications.
To provide maximum value for readers, the metadata needs to be consistent, which is where the Schema.org Accessibility Properties for Discoverability Vocabulary [[a11y-discov-vocab]] comes in. This vocabulary defines controlled sets values to use with each property (with the exception of summaries, which are free-form text).
But even with a controlled vocabulary, as schema.org is intended to describe any resource on or referenced from the web, the value definitions do not always fully reflect how to apply them to EPUB publications. That is where this guide fits in. Its goal is add clarity on how to apply the metadata to both reflowable and fixed-layout EPUB publications.
An access mode is defined as a "human sense perceptual system or cognitive faculty through which a user may process or perceive the content of a digital resource." [[iso24751-3]] For example, if an EPUB publication contains images and video, visual perception is required to consume the content exactly as it was created.
There are four access modes that are typically specified for EPUB publications:
textual — the publication contains text content (headings, paragraphs, etc.).
visual — the publication contains visual content such as images, graphics, diagrams, animations, and video.
auditory — the publication contains auditory content such as standalone audio clips and audio soundtracks for video content.
tactile — the publication contains tactile content such as embedded braille and tactile diagrams.
Access modes are set in the [[schema-org]] accessMode property. Repeat the property for each access mode.
For a user to determine whether an EPUB publication is suitable for their needs, they need to know
which access modes are required to consume the content. List all applicable access modes in the
[[schema-org]] accessMode property,
repeating the property for each applicable mode.
Do not list access modes for content that does not contain information necessary to
understand a publication. Most EPUB publications contain cover images, for example, but it is not
necessary to see the cover image to read the publication. The same is true of publisher logos and
images in the content are only for presentational purposes (i.e., have no information so have empty
[[html]] alt attribute values). If these are the only visual content, then it is not
valid to list a visual access mode. Similarly, if the only audio an EPUB publication contains is
background music (e.g., for an instructional video with text captions, or as mood music while
reading), listing an auditory access mode is not valid.
Note that the access modes of the content do not reflect any adaptations that have been provided. For example, if a comic book also includes alternative text for each image, it does not have a textual access mode. See the following section on sufficient access modes for how to indicate that the available adaptations allow the content to be consumed in another mode.
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.
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.
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.
If the only images within the EPUB are: cover, author, corporate logos, or decorative
images the accessMode of 'visual' would not be included in the
metadata.
Indicates that the resource contains text encoded in visual form.
Setting the correct access modes and sufficient access modes for EPUB 3 publications that contain synchronized text-audio playback requires evaluating whether playback is essential to reading the publication or an additional feature.
EPUB 3's media overlays [[epub-3]] allows EPUB creators to synchronize the full text of a publication with full audio narration. These types of publications are commonly referred to as "read aloud" books, as the user chooses whether or not to turn on the narration (unlike traditional audiobooks where only the audio is available).
In this case, because the audio playback is an extra feature, EPUB creators would
not list "auditory" as an access
mode. Rather, they would indicate the presence of text and audio synchronization as an
accessibility feature:
<meta
property="schema:accessibilityFeature">
synchronizedAudioText
</meta>
Although the audio is not essential to reading the publication, having full audio playback
capability means that there is an auditory sufficient access
mode — the user can listen to the complete publication. Consequently, the EPUB
creator would declare a schema:accessModeSufficient property with the value
auditory:
<meta
property="schema:accessModeSufficient">
auditory
</meta>
When media overlays are present, EPUB creators should not add "auditory" to all
the possible sufficient access modes just because it is possible to turn on text-audio
playback.
For example, a publication with media overlays that has text and images (with text
alternatives) would only declare the following sufficient access modes:
"textual", "auditory", and "textual,visual".
It would not declare "textual,auditory" or
"textual,visual,auditory".
Another use for media overlays — more typical among accessible republishers such as libraries that serve blind and low vision readers — is to provide full audio synchronized to the major headings of a publication. These types of publications are more like traditional audiobooks, as all the information in the work is typically available in auditory form. The minimal text does not allow meaningful visual reading or text-to-speech playback; it is only to provide structured navigation capabilities.
In this case, being able to hear the audio is essential to being able to read the publication, so EPUB creators will list an auditory access mode:
<meta
property="schema:accessMode">
auditory
</meta>
In a reverse of the first case discussed, EPUB creators will not identify text-audio synchronization as a feature of the publication since the amount of text provided is trivial.
Likewise, since the text in the publication only provides heading navigation, EPUB creators will not list a textual access mode. The user does not need to, and is not expected to, visually read this text.
Some publications that provide the body in auditory form may include the backmatter in text form, allowing users to use text-to-speech playback to render it. In this case, there would be a textual component.
The access modes sufficient to consume an EPUB publication express a broader picture of the potential usability than do the basic access modes. Where the basic access modes identify the default nature of the media used in the publication, sufficient access modes identify all the individual modes, and sets of modes, that allow a user to read a publication. Sufficient access modes account for the affordances and adaptations that the EPUB creators have provided, allowing users to determine whether they can the read content regardless of its default nature.
Sufficient access modes are identified in the [[schema-org]] accessModeSufficient property.
Repeat the property for each set of sufficient access modes.
The most strongly recommended sufficient access modes to list are the ones that consist of only a single value. Users seeking alternatives to the default encoding of the information typically want to read the content without switching reading modes (e.g., they want a purely textual alternative to use text-to-speech playback or an auditory alternative to listen to prerecorded narration). Listing the single value sets allows users to easily determine whether a publication will meet their reading needs.
The most common single sufficient access modes for EPUB publications are:
textual — setting this value indicates that the publication is screen-reader
friendly (i.e., all the content is available for text-to-speech rendering by an assistive
technology). EPUB creators can set this value for EPUB publications that conform to Level A [[wcag2]] or higher, for example, as
there must be textual alternatives for non-text content to meet these thresholds.auditory — setting this value indicates that pre-recorded audio is available
for the publication. EPUB creators can set this value for EPUB publications that provide media
overlays for all the content.As an example of setting sufficient access modes, consider an EPUB publication that contains graphics
and charts, as well as descriptions for all these images. The publication has both textual and
visual content, so the EPUB creator will
include the following schema:accessMode metadata entries to indicate this:
<meta
property="schema:accessMode">
textual
</meta>
<meta
property="schema:accessMode">
visual
</meta>
This metadata does not make clear whether a textual access mode is sufficient to read the entire publication, or whether a visual one is, only that the user requires the ability to read in those two modes by default. This discrepancy is why sufficiency is also important to know.
Since the EPUB creator has also included textual alternatives and/or descriptions for all the images in the example publication, the metadata can also indicate that a purely textual access mode is sufficient to read the content:
<meta
property="schema:accessModeSufficient">
textual
</meta>
Without this metadata, users would not have known that they could read the publication only via its textual content.
It is important to emphasize when listing individual values in the
schema:accessModeSufficient property not to simply restate each individual access
mode. When adding a schema:accessModeSufficient property with only a single value,
all information in the publication must be available in that mode.
For example, the EPUB creator would not declare a sufficient access mode of "visual" for
the example publication as the information is not entirely available in image-based form. (Photo
books without text would be examples of works with a purely visual sufficient access mode.)
EPUB creators may also list any sets of sufficient access modes that allow full access to the information. As the most typical set of values is the combination of all the access modes, however, the information this provides users is less helpful in determining the usability of a publication.
For example, the metadata the EPUB creator inputs for the example publication re-establishes that there is a textual and visual reading option:
<meta
property="schema:accessModeSufficient">
textual,visual
</meta>
The order in which EPUB creators list the access modes in a set is not important. The only requirement is to separate the values by commas.
The complete set of schema:accessMode and schema:accessModeSufficient
entries for the example publication is as follows:
<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>
Note that sufficiency of access is often a subjective determination of the EPUB creator based on their understanding of what information is essential to comprehending the text. Some information loss occurs by not being able to view a video, for example, but the EPUB creator might regard the visual or auditory losses as inconsequential if a transcript provides all the necessary information to understand the concepts being conveyed.
Refer to The
accessModeSufficient Property [[a11y-discov-vocab]] for more information
about this property and its values.
The accessModeSufficient property, as defined in [[schema-org]], allows more
complicated expressions than can be represented in the EPUB 2 or 3 package document (e.g.,
definition of lists of values and inclusion of a human-readable description). A future version
of EPUB might allow for richer metadata, but the basic expression shown in this section is
sufficient for discovery purposes.
Having a single accessModeSufficient implies that the entire content of the EPUB can
be consumed with only that mode of accessing the content within the book.
Indicates that only visual perception is necessary to consume the information.
An example of this would be a children's picture book.
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 embossed as braille for tactile reading.
An example of this would be a romance novel.
Indicates that auditory perception is necessary to consume the information.
An example of this would be an audio book.
Combining various accessModeSufficients implies that a combination of access modes
are required to completely consume and understand the content within the EPUB.
Indicates that both visual perception and the ability to read textual content is necessary to consume the information.
An example of this would be a cookbook.
Indicates that both visual perception and the ability to hear the content is necessary to consume the information.
An example of this would be a narrated picture book.
Indicates that both the ability to hear the content and read textual content is necessary to consume the information.
Examples of this would be an an audio book with synchronized text highlighting, or an interactive dictionary where you could hear the pronunciation of the defined words.
Identifying all the accessibility features and adaptations included in an EPUB publication allows users to determine whether the content is usable at a more fine-grained level than the access modes do.
For example, a math textbook might have a textual access mode, but that alone does not indicate whether MathML markup is available. Whether a visual work only provides alternative text or whether it includes extended descriptions is also important to know when gauging its usability.
Accessibility features are identified in the [[schema-org]] accessibilityFeature property.
Repeat this property for each feature.
The EPUB format requires that some accessibility features will always be present (e.g., a table of contents). Do not exclude these features from the accessibility metadata, as users typically are not aware what features are built into a format. Failing to include entries will reduce the discoverability of the publication when users search for specific features.
Be aware that although the vocabulary for the accessibilityFeature property [[a11y-discov-vocab]] contains the values
"none"
and "unknown", these terms cannot be used to meet the reporting requirements
for the property. Authors must indicate at least one feature that is not one of these values to
claim conformance to EPUB Accessibility 1.1.1 [[epub-a11y-111]].
Refer to The
accessibilityFeature Property [[a11y-discov-vocab]] for more information
about this property and its values.
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 LaTeX 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.
Unsupported Terms include those features that are currently not supported in EPUB.
Alternative text is provided for visual content. In fixed layout books this would typically be in the form of textual descriptions of the images contained within the publication.
Audio descriptions are available (e.g., via an HTML track element with its
kind attribute set to "descriptions").
Indicates that synchronized closed captions are available for audio and video content.
Closed captions are defined separately from the video, allowing users to control whether they are rendered or not, unlike open captions which would be rendered directly onto the video during the video editing process, becoming a permanent part of the visual content.
Textual descriptions of math equations are included in the alt attribute for image-based equations, or by other means.
Descriptions are provided for image-based visual content and/or complex structures such as tables, mathematics, diagrams, and charts.
Indicates that synchronized open captions are available for audio and video content.
Open captions are part of the video stream and cannot be turned off by the user, unlike closed captions.
Sign language interpretation is available for audio and video content.
Indicates that a transcript of the audio or video content is available.
Indicates that the visual presentation of the text can be transformed by the user to meet their reading requirements. This includes the ability to resize text, adjust line spacing and margins, change fonts, and modify color contrast (e.g., for a light, dark, or sepia mode).
This feature is characteristic of reflowable EPUBs that are built with semantic HTML and flexible CSS, avoiding practices that lock down the presentation, such as hard-coding sizes in absolute units or embedding text in images.
Indicates that the EPUB contains synchronized pre-recorded audio narration that matches the text of the document, commonly known as a Media Overlay. The reading system can highlight units of text as they are spoken.
Indicates that the user can control the timing of any time-based interaction to meet their needs. This allows the user to turn off, adjust, or extend time limits on activities like tests or forms.
For more details see Success Criterion 2.2.1 Timing Adjustable.
This feature is critical for users who may require more time to read, comprehend, or respond to content.
No digital rights management or other content restriction protocols have been applied to the resource.
The absence of DRM is a critical accessibility feature as it ensures that users can access the content with their preferred assistive technologies, which might otherwise be blocked by encryption. It allows for personal use and transformations of the content that may be necessary for a user to perceive and understand it (e.g., using it with specialized text-to-speech software).
Identifies that the LaTeX typesetting system is used to encode chemical equations and formulas.
In this method, the raw LaTeX source is embedded directly in the content document. A JavaScript-based rendering engine, such as MathJax, should then be used to convert this source into a visually and accessibly rendered formula.
Identifies that the Mathematical Markup Language (MathML) is used to encode chemical equations and formulas. MathML provides a structured, semantic representation that can be rendered directly by modern browsers and assistive technologies.
This method provides a robust, accessible alternative to images, as the notation can be resized, searched, copied, and interpreted correctly by screen readers.
Identifies that the LaTeX typesetting system is used to encode mathematical or other scientific notations.
In this method, the raw LaTeX source is embedded directly in the content document. A JavaScript-based rendering engine, such as MathJax, should then be used to convert this source into a visually and accessibly rendered formula.
Identifies that the Mathematical Markup Language (MathML) is used to encode mathematical equations and formulas. MathML provides a structured, semantic representation that can be rendered directly by modern browsers and assistive technologies.
This method provides a robust, accessible alternative to images, as the notation can be resized, searched, copied, and interpreted correctly by screen readers for proper speech output or even braille display.
One or more of [SSML], [Pronunciation-Lexicon], and [CSS3-Speech] properties has been used to enhance text-to-speech playback quality.
These technologies allow an author to resolve ambiguities and improve the clarity of synthesized speech by correcting mispronunciations of names or jargon, indicating emphasis, and controlling the pacing and prosody of the narration.
Indicates that pre-recorded audio-only content with speech in the foreground meets the contrast requirements of WCAG 1.4.7 Low or No Background Audio (AAA).
This feature ensures that users who are hard of hearing or have difficulty processing speech with background noise can clearly understand the primary audio content.
Indicates that the content's default visual presentation of text and images of text meets the enhanced contrast thresholds set out in WCAG Success Criterion 1.4.6 (AAA).
This ensures legibility for users with low vision or color vision deficiencies who require a higher-than-normal contrast between text and its background to read comfortably.
The content has been formatted to meet large print guidelines.
This property should only be used for fixed-layout content where the font size cannot be adjusted by the user. For reflowable content where the font size can be increased, the displayTransformability property should be used instead.
The content is in braille format, or alternatives are available in braille.
This feature indicates that the publication contains content represented by braille characters, which is essential for specialized notations like mathematics (Nemeth) or music that do not convert reliably from standard text. It can also refer to the availability of a separate, physical braille version.
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.
In a digital publication, this typically means that digital files for creating embossed graphics are included, or that a physical tactile version is available as a companion. Tactile graphics provide essential access to non-textual information like maps, charts, and diagrams for readers who are blind or have low vision.
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.
In a digital publication, this means the book provides downloadable files for use with devices like 3D printers. Tactile objects provide crucial access to spatial and structural information for complex subjects like biology or architecture, allowing readers who are blind to explore shapes by touch.
Indicates that ruby annotations are attached to every CJK ideographic character in the content.
Ruby annotations are used as pronunciation guides for logographic characters in languages like Chinese, Japanese, and Korean. They make difficult CJK ideographic characters more accessible for language learners, native speakers of all reading levels, and people with reading disabilities. They also provide critical information for text-to-speech (TTS) engines.
If some but not all CJK ideographic characters have ruby annotations, the rubyAnnotations value should be used instead.
Indicates that the content can be laid out horizontally (e.g, using the horizontal-tb writing mode of [[css-writing-modes-3]]).
This value should only be set when the language of the content allows both horizontal and vertical directions. Notable examples of such languages are Chinese, Japanese, and Korean. Providing a horizontal layout is a critical accessibility feature for some users with reading disabilities who find vertical text difficult to process.
Indicates that ruby annotations are attached to some but not all CJK ideographic characters in the content.
This practice provides targeted pronunciation support for rarer characters, proper nouns, or key terms without cluttering the text with ruby on every single character. It's a common authoring pattern that aids comprehension for a wide range of readers.
If all CJK ideographic characters have ruby annotations, use the fullRubyAnnotations value.
Indicates that the content can be laid out vertically (e.g, using the vertical-rl of [[css-writing-modes-3]]).
This value should only be set when the language of the content allows both horizontal and vertical directions. Notable examples of such languages are Chinese, Japanese, and Korean. Providing a vertical layout is essential for publications that follow traditional typesetting conventions for these languages and can improve readability for many native readers.
Indicates that the content can be rendered with additional word segmentation.
Adding visual separators between words in languages that do not typically use them is a critical accessibility feature for some users with reading disabilities, such as dyslexia, as well as for language learners.
Indicates that the content can be rendered without additional word segmentation.
This indicates that the content is presented in its standard format for languages that do not typically use spaces between words (e.g., Japanese, Chinese, Thai). For fluent readers, this provides the expected, natural reading experience without the potential distraction of artificial word spacing.
Indicates that the resource does not contain any accessibility features.
This value is mutually exclusive and must not be set if any other accessibilityFeature value is also present. Declaring the none value provides an explicit and unambiguous statement that no specific accessibility features have been included, which aids in content discovery. This is different from a publication that simply omits all accessibility metadata.
Indicates that the author has not yet checked if the resource contains accessibility features. This value is only intended as a placeholder until an accessibility review can be completed.
This value is mutually exclusive and must not be set if any other accessibilityFeature value is also present. Declaring unknown acts as a temporary placeholder, explicitly stating that an accessibility audit has not yet been performed. It distinguishes the content from a publication that has been audited and confirmed to have no features (see none).
Definition: The resource includes annotations from the author, instructor and/or others.
Status: Deprecated
Reasoning: The use of the annotations value is now deprecated due to the general nature of annotations in published works. When authors or publishers add annotations to a work, they provide information for all readers; they are not used as a means of enhancing otherwise inaccessible content.
Definition: The work includes bookmarks to facilitate navigation to key points.
Status: Deprecated
Reasoning: The use of the bookmarks value is now deprecated due to its ambiguity. Reading systems typically provide bookmark support not the EPUB itself.
Definition: Indicates that synchronized captions are available for audio and video content.
Status: Deprecated
Reasoning: The use of the captions value is now deprecated. Authors should use the more specific closedCaptions or openCaptions values, as appropriate.
Definition: Indicates that chemical notations, such as molecular formulas and reaction diagrams, are represented in a structured format.
Status: Unsupported. Although the metadata value is ChemML, the underlying format it actually identifies is the Chemical Markup Language (CML).
Reasoning: There is no native support for CML in HTML. Because EPUB content is built on web standards, the vast majority of e-reader devices cannot render CML visually, making this feature unreliable without a fallback image. The name also causes significant confusion with the unrelated 'ChemML' Python library for machine learning. Here is a link to the CML (Chemical Markup Language) specification.
Definition: The resource includes print page numbers.
Status: Deprecated
Reasoning: The metadata term printPageNumbers value has been replaced by pageBreakMarkers.
Definition: Indicates that a PDF document's contents have been tagged to create a logical structure, permitting access by assistive technologies.
Status: Unsupported. This metadata property is exclusively for describing PDF documents and is not relevant in the context of an EPUB file.
Reasoning: EPUB and PDF are fundamentally different technologies. An EPUB's accessibility is achieved through its use of semantic HTML and ARIA, while a PDF's accessibility relies on its internal tagging structure. An EPUB's metadata must describe the features of the EPUB itself. Applying a PDF-specific property like taggedPDF is inappropriate and would be ignored by reading systems. While an EPUB might link to an external PDF, the metadata for the EPUB should not describe the features of that external file.
There are three widely recognized hazards that can affect readers of digital content:
flashing — if a resource flashes more than three times a second, it can cause seizures (e.g., videos and animations). See also Guideline 2.3 [[wcag2]].
motion simulation — if a resource simulates motion, it can cause a user to become nauseated
(e.g., a video game drawn on the [[html]] canvas element or parallax scrolling with CSS).
sound — certain sound patterns, such as ringing and buzzing, can cause seizures, while loud or sudden changes in volume can also negatively affect users.
EPUB creators have to report whether their EPUB publications contain resources that present any of these hazards to users, as they can have real physical effects.
What precisely constitutes a sound hazard, and how to test for these hazards, is not standardized as of publication of this document. EPUB creators will have to use their discretion on when to specify a sound hazard until additional guidance is developed. This technique will be updated whenever there is more clarity on this issue.
Hazards are identified in the [[schema-org]] accessibilityHazard property. Repeat this property for each hazard.
Unlike other accessibility properties, the presence of hazards can be expressed both positively and
negatively. This design decision was made because users most often search for content that is free
from hazards that affect them, but also want to know what dangers are present in any publications
they discover. To indicate that hazards are not present, use the values
"noFlashingHazard", "noMotionSimulationHazard", and
"noSoundHazard".
Do not skip reporting hazards just because an EPUB publication does not contain any content that
could present risks. Users cannot infer a meaning when no metadata is present. The value
"none" can be used in such cases instead of repeating each non-hazard. When the
"none" value is used, no other hazards values may be specified.
If an EPUB publication contains a hazard, provide additional information about its source and nature in the accessibility summary.
If an EPUB creator cannot determine if a publication presents a specific hazard for users, list that
hazard as unknown. The following values are used to identify individual unknown hazards:
"unknownFlashingHazard", "unknownMotionSimultationHazard", and
"unknownSoundHazard".
For example, determining whether sound hazards are present can be challenging as the causes are
currently not well defined. In this case, EPUB creators may prefer to set the
"unknownSoundHazard" value, as in the following example.
If it is not possible to determine any hazards, the value "unknown" can be used in place
of setting the individual hazards to unknown. This value should be used sparingly, however, as it is
of no value to users. EPUB creators should make every effort to determine if hazards are present.
When the "unknown" value is set, no other hazard values may be specified.
EPUB creators must ensure that information about all three types of hazards is included when not
using the "unknown" or "none" values.
Refer to The
accessibilityHazard Property [[a11y-discov-vocab]] for more information
about this property and its values.
Indicates that the resource presents a flashing hazard for photosensitive persons. This value should be set when the content contains flashing that fails to meet the safety thresholds described in Success Criterion 2.3.1 Three Flashes or Below Threshold (A).
The flashing value must not be set when any of the noFlashingHazard, unknownFlashingHazard, none, or unknown values is set.
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.
This hazard can trigger severe dizziness, nausea, and disorientation in users with vestibular disorders. Declaring this hazard is a critical safety warning.
The motionSimulation value must not be set when any of the noMotionSimulationHazard, unknownMotionSimulationHazard, none, or unknown values is set.
Indicates that the resource contains auditory sounds that may affect some individuals. This value should be set when any audio on the page plays automatically for more than three seconds without a user control mechanism, as this fails Success Criterion 1.4.2 Audio Control.
Automatically playing audio can interfere with screen reader output, making the page unusable for blind or low-vision users. Declaring this hazard is a critical usability warning.
The sound value must not be set when any of the noSoundHazard, unknownSoundHazard, none, or unknown values is set.
The application of this value is currently under discussion as its application is underspecified.
Indicates that the resource does not contain any hazards.
It is recommended to use the none value when there are no hazards instead of individual statements for noSoundHazard, noMotionSimulationHazard, and noFlashingHazard.
The none value is mutually exclusive. It must not be set when specifying a known hazard (e.g., flashing), an unknown hazard status (e.g., unknownFlashingHazard), or individual statements of safety (e.g., noFlashingHazard).
Indicates that the resource does not present a flashing hazard. This means the content has been checked and meets the safety thresholds described in Success Criterion 2.3.1 Three Flashes or Below Threshold (A).
This value provides a positive assertion that the content is safe for users with photosensitive epilepsy. It is a critical piece of metadata for ensuring user safety and building trust.
The noFlashingHazard value must not be set when any of the flashing, unknownFlashingHazard, unknown, or none values is set.
Indicates that the resource does not contain instances of motion simulation.
This value provides a positive assertion that the content is safe for users with vestibular disorders. It is a critical piece of metadata for ensuring user safety and building trust.
The noMotionSimulationHazard value must not be set when any of the motionSimulation, unknownMotionSimulationHazard, unknown, or none values is set.
Indicates that the resource does not contain auditory hazards. This means the content has been checked and does not contain audio that plays automatically for more than three seconds, meeting Success Criterion 1.4.2 Audio Control.
This value provides a positive assertion that the content will not interfere with screen readers or other assistive technologies.
Editor's note: The application of this value is currently under discussion as its application is underspecified.
The noSoundHazard value must not be set when any of the sound, unknownSoundHazard, unknown, or none values is set.
Indicates that the author is not able to determine if the resource presents any hazards.
It is recommended to use the unknown value when the status of all hazards is unknown, instead of listing individual statements for unknownSoundHazard, unknownMotionSimulationHazard, and unknownFlashingHazard.
The unknown value is mutually exclusive. It must not be used in combination with any known hazard (e.g., flashing), the none value, or any individual unknown hazard statement (e.g., unknownFlashingHazard).
Indicates that the author cannot determine if a flashing hazard exists.
This value is a placeholder for a specific hazard, indicating that it has not yet been evaluated. It allows for a partially completed hazard assessment, unlike the global unknown value.
The unknownFlashingHazard value must not be set when any of the flashing, noFlashingHazard, none, or unknown values is set.
Indicates that it is unknown if a motion simulation hazard exists within the content.
This value is a placeholder for a specific hazard, indicating that it has not yet been evaluated. It allows for a partially completed hazard assessment, unlike the global unknown value.
The unknownMotionSimulationHazard value must not be set when any of the motionSimulation, noMotionSimulationHazard, none, or unknown values is set.
Indicates that it is unknown if an auditory hazard exists within the content.
This value is a placeholder for a specific hazard, indicating that it has not yet been evaluated. It allows for a partially completed hazard assessment, unlike the global unknown value.
The unknownSoundHazard value must not be set when any of the sound, noSoundHazard, none, or unknown values is set.
An accessibility summary provides a brief, human-readable description of the accessibility characteristics of an EPUB publication that cannot be expressed through the other discovery metadata.
An accessibility summary is provided using the [[schema-org]] accessibilitySummary property.
The accessibility summary should not simply repeat the conformance information provided in the
dcterms:conformsTo property, for example, or the features listed in the
schema:accessibilityFeature properties. When other accessibility metadata is
present in the package document, systems that process EPUB publications can already present it to
users. Repeating it in the summary only makes them hear the information again.
EPUB creators should not include an accessibility summary when they have nothing more to add to the conformance claim and other discovery metadata.
If an EPUB publication does not meet the requirements for content accessibility in [[epub-a11y-111]], the reason(s) it fails should be noted in the summary. Similarly, if an EPUB creator is hesitant to make a formal claim of conformance, the reasons why can be explained in the summary.
Do not repeat this property to provide translations of a summary. EPUB does not define a method for
including translations. Putting different xml:lang attributes on properties does not
indicate a translation and could lead to wrong summary being rendered to users.
It is not necessary to set the schema:accessibilityAPI property for EPUB publications. EPUB creators are not responsible for the
interaction between reading systems
and the underlying platform APIs.
It is not necessary to set the schema:accessibilityControl property for EPUB publications. This property does
not differentiate issues arising from the reading system interface from those in the underlying content, which has led to confusion about
its use.
Meeting the requirements of [[wcag2]] will mitigate most known issues with the content and is sufficient for authoring purposes.
The following examples show the metadata that would be added to an EPUB publication that has textual and visual access modes, is sufficient for reading by text, contains alternative text and MathML markup, and has a flashing hazard.