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Axe Core Guide

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Find out what web pages on your sites are affected by HTML issues.

Axe Core 4.9

IDs of active elements must be unique

The value supplied to active ID attributes on focusable elements must be unique to avoid assistive technology from overlooking the second instance. Active ID attributes may not be used more than once on focusable components inside the same document; assistive technology requires unique IDs for focusable active elements in order to differentiate between them.

Focusable components on a page are identified exclusively by the ID attribute. It is illogical to duplicate an active ID.

Duplicate active ID values compromise the accessibility of focusable elements, such as form labels, table header cells, and so on. Screen readers and client-side scripts will bypass all instances of repetition other than the first. Validating HTML files aids in preventing and eliminating potential sources of accessibility issues, so long as accessibility is not compromised.

Those who have expertise with client-side scripting are aware that when an active ID is reused, the only instance that is normally acted upon by the script is the first. Similarly, assistive technology may only appropriately reference the first active ID when mentioning it.

What this Accessibility Rule Checks

Ensures that each page element with an active ID and a focusable state has a unique value.

Learn more:

Related Accessibility Rules