Definition

A characteristic of the described resource that is physiologically dangerous to some users. Related to WCAG 2.1 guideline 2.3.

Examples

Example 1 — EPUB 3
<meta property="schema:accessibilityHazard">flashing</meta>
Example 2 — EPUB 2
<meta name="schema:accessibilityHazard" content="flashing"/>
Example 3 — Audiobooks
"accessibilityHazard": ["flashing"]
Example 4 — HTML with RDFa
<p><strong>Warning</strong>: <span
property="accessibilityHazard">flashing</span> 
in this video may cause seizures in some 
individuals.</p>
Example 5 — HTML with microdata
<p><strong>Warning</strong>: <span
itemprop="accessibilityHazard">flashing</span> 
in this video may cause seizures in some 
individuals.</p>

Values

The following values are used to identify potential hazards (or the lack thereof) so that users with such sensitivities know what to expect in advance:

flashing

The flashing values is used to indicate that there is content in the publication that flashes more than three times a second or that the flashing is below the general flash and red flash thresholds.

These flashing hazards can cause headaches and seizures for users who are photosensitive. In addition to setting this value, the publication should include warnings wherever such content is located.

Although videos are often recognized as a source of flashing hazards (e.g., strobe effects), there are many types of content that can present a flashing risk (e.g., animated graphics, and scripted games and images).

noFlashingHazard

The noFlashingHazard value is the opposite of flashing — it is used to indicate that the the publisher has checked the publication for flashing hazards and is sure that none exist.

The value is not an indication that a lack of flashing is a hazard.

none

The none value is used when the publisher is sure that the content presents no known hazards for users.

This value is typically only used with there is no dynamic or multimedia content (i.e., the publication consists only of text and/or static images).

motionSimulation

The motionSimulation value is used to indicate that there is content that simulates motion.

Motion simulation can cause headaches and nausea in some users. In addition to setting this value, the publication should include warnings wherever such content is located.

Motion simulation can occur in a variety of media: videos or games with a first-person perspective, 3D experiences and animations, etc.

noMotionSimulationHazard

The noMotionSimulationHazard value is the opposite of motionSimulation — it is used to indicate that the the publisher has checked the publication for motion simulation hazards and is sure that none exist.

The value is not an indication that a lack of motion simulation is a hazard.

sound

The sound value is used to indicate that a publication contains auditory content that can cause seizures in some users. The causes of such seizures are diverse, from ringing and buzzing sounds, to sudden loud noises, and even certain words or music.

Out of an abundance of caution, this property should be set if a publication contains any auditory content, and users should always have the decision whether or not to play the content (i.e., auditory content should not autoplay).

noSoundHazard

The noSoundHazard value is the opposite of sound — it is used to indicate that the the publisher has checked the publication for sound hazards and is sure that none exist.

The value is not an indication that a lack of sound is a hazard.

unknown

The unknown value is used to indicate that a publisher has not yet checked their publication for hazards or is unsure whether some content might present a hazard.

This value should only be used as a temporary placeholder if a publication must be released before an accessibility review can be completed.

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