id attribute value must be unique

To avoid assistive technology missing the second instance, the value supplied to an id property must be distinct. In other words, id attributes may not be used more than once to distinguish one element from another within the same document.

Elements on a page are uniquely identified via the ID attribute. It makes no sense to make a second id.

Duplicate ids can make labels for forms, table header cells, etc. inaccessible since screen readers and client-side scripts pass over the second iteration. They are typical markup validation mistakes that, if they do not damage accessibility, can reduce potential causes of accessibility issues.

Those who are familiar with client-side scripting are aware that when an ID is reused, the script normally only reacts to the first instance of that id use. Similar to this, assistive technology might only appropriately reference the first id when referencing an id.

What this Accessibility Rule Checks

Makes certain that every element on the page with an id attribute has a distinct value for the id attribute.

Learn more:

Deque Reference

Deque University - How To Fix

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W3C Reference

WCAG 2.1 - Failure of Success Criterion 4.1.1 due to duplicate values of type ID

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