ISSUE WITH THE TABLE ROW HEADER MISSING OPENING PARENTHESIS
SC 2.3.1 Three Flashes or Below Threshold
Prevent content that could trigger photosensitive seizures.
- Flash Limit: Ensure no content flashes more than three times in any one-second period.
- Thresholds: Content must remain below established general flash and red flash thresholds.
- Exceptions: Flashes that are small in size relative to the user’s field of vision or that consist of low-contrast, balanced patterns (e.g., white noise).
- Guidance: When flashing content is unavoidable (e.g., in third-party video), test for compliance; otherwise, avoid flashing content entirely.
2.3.1 Three Flashes or Below Threshold: web pages do not contain anything that flashes more than three times in any one second period, or the flash is below the general flash and red flash thresholds.
SC 2.3.1 Three Flashes or Below Threshold supports the accessibility principle of Operable because it ensures that people who have photosensitive seizure disorders, such as photosensitive epilepsy, will be able to view and operate all the content and controls on a screen or Web page without having a seizure and without having to miss the full experience of the content by being limited to text alternatives.
Flashing can be caused by the display, the computer rendering the image, or by the content being rendered. Since the author or developer has no control of the first two, which can be affected by the design and speed of the display and computer, the intent of this SC is to ensure that flicker that violates this criterion is not caused by the content itself.
Individuals who have photosensitive seizure disorders can have a seizure triggered by content that flashes or flickers more than three times per second. These users may also be more sensitive to saturated red flashing content. As such, it’s best to avoid providing such content.
Flashing content that does not exceed a certain size in the user’s field of vision (the “flash threshold” size) is allowed, as well as flashing content that is a fine, balanced, pattern such as white noise.
Since any content that does not meet this SC can interfere with a user’s ability to use the whole page, all content on a screen or Web page must meet this SC. Failing to meet this SC represents a risk of causing seizures in people who have photosensitive seizure disorders.
Impact of Nonconformance with SC 2.3.1 Three Flashes or Below Threshold
| Type of Disability | Description of Impact |
|---|---|
| Photosensitive (epilepsy/photosensitive seizure disorders) | Some users may be vulnerable to seizures from content that flashes, blinks, or pulses. Flashing could, therefore, interfere with a user’s ability to interact with content or could make the content entirely unusable. Content designers and developers must not include any content that could cause seizures. |
Applicability of Success Criteria 2.3.1 Three Flashes or Below Threshold
| Technology | Applicability of SC 2.3.1 Three Flashes or Below Threshold |
|---|---|
| All (Web, Software, Office documents, PDFs, Mobile Native) | Flashing content could be included in a video, in animations, or in content that is coded to flash between certain color states and at certain frequencies. When flashing content originates from a video or animation that the author or developer may not be able to control, then they must perform their own tests to determine whether the content is within the allowable thresholds set in SC 2.3.1. If a content author or developer creates the content, then they must ensure that whatever method they use can limit the flash rate and/or contrast between flash states to stay within the allowable threshold limits. In most cases, however, it is best just to avoid flashing content altogether. |