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WCAG: 4.1.1: IDs used in ARIA and labels must be unique
The value assigned to an ARIA ID must be unique to prevent the second instance from being overlooked by assistive technology. Put another way; ARIA ID values may not be used more than once in the same document to differentiate each element from another.
Duplicate ARIA IDs are common validation errors that may break the accessibility of labels, e.g., form fields, table header cells.
Unique ID's differentiate each element from another and prevent invalid markup, wherein only the first instance gets acted upon by client-side scripting, or where assistive technologies typically only reference the first one accurately.