Three Flashes or Below Threshold
Web pages must not contain anything that flashes more than three times in any one-second period, unless the flashing is below specific brightness thresholds.
What it requires
WCAG 2.0 SC 2.3.1 protects users with photosensitive epilepsy and migraine sensitivity. Flashing content that exceeds three flashes per second in a sufficiently bright/contrasting region can trigger seizures.
The threshold is technical: the flashing must stay below 25% screen area or below specific luminance/red-flash thresholds. In practice, ecommerce sites should avoid flashing content entirely except for very small UI accents.
Common Shopify failure
Promotional carousel that auto-cycles every 0.3 seconds with high-contrast color shifts. Flash-sale banner with rapid red/yellow color flashing.
How to fix it
Remove potentially hazardous flashing or evaluate it with an appropriate flash-analysis tool. CSS timing alone cannot establish whether content falls below the WCAG luminance, area, and red-flash thresholds.
Merchant QA checklist
- Scan the storefront page where this pattern appears: product pages, collection pages, cart drawer, customer-account pages, and any landing page built with theme sections.
- Confirm the issue is fixed in the rendered browser output, not only in the Liquid file. Shopify section settings, app blocks, and third-party scripts can reintroduce the same 2.3.1 failure after a theme edit.
- Re-test the affected component with keyboard navigation and a screen-reader accessibility tree before publishing the theme, especially when the fix changes markup or ARIA attributes.
How AccessComply handles it
AccessComply uses automated rules to check supported patterns in the pages reached during a scan. Some WCAG requirements need human judgment, assistive-technology testing, or access to third-party content and cannot be established by an automated scan. This criterion is generally treated as a guided or hands-on fix pattern. If the app can safely match the issue to supported source code, the merchant must review and approve the suggested change before anything is written, and the result is checked afterward. Otherwise the merchant should use the guidance above and independent hands-on testing. The label is not a guarantee of detection, a fix, WCAG conformance, or legal compliance.
Primary source: W3C — WCAG 2.0 Understanding 2.3.1