Accessibility Checking for Large Sites
Rocket Validator integrates axe-core version 4.1,
which currently checks 91 accessibility rules, into an automated web site scanner.
ID attribute value must be unique
The value assigned to active ID attributes on focusable elements must be unique to prevent the second instance from being overlooked by assistive technology. Put another way, active ID attributes may not be used more than once on focusable elements in the same document; focusable active elements require unique IDs for assistive technology to distinguish one element from another.
The ID attribute uniquely identifies focusable elements on a page. It does not make sense to duplicate an active ID.
Duplicate active ID values break the accessibility of focusable elements including labels for forms, table header cells, etc., Screen readers and client-side scripts will skip any duplication other than the first instance. Validating HTML files help prevent and eliminate possible sources of accessibility problems, when not breaking accessibility.
Those experienced with client-side scripting know that when you re-use an active ID, typically the only one that gets acted upon by the scripting is the first instance of the use of that active ID. Similarly, assistive technologies may, when referencing an active ID, only reference the first one accurately.
Learn more about this accessibility rule at Deque University >>
Other WCAG: 4.1.1 accessibility rules checked by Rocket Validator
The value assigned to an ID attribute must be unique to prevent the second instance from being overlooked by assistive technology. Put another way; ID attributes may not be used more than once in the same document to differentiate each element from another.
The ID attribute uniquely identifies elements on a page. It does not make sense to duplicate an ID.
Duplicate ID's can break the accessibility of labels for forms, table header cells, etc., by the second instance being skipped by screen readers, or by client-side scripts. They are common markup validation errors that can eliminate possible sources of accessibility problems, when not breaking accessibility.
Those experienced with client-side scripting know that when you re-use an id, typically the only one that gets acted upon by the scripting is the first instance of the use of that ID. Similarly, assistive technologies may, when referencing an id, only reference the first one accurately.
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.