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Technique H93:Ensuring that id attributes are unique on a Web page


All HTML pages

This technique relates to 4.1.1: Parsing (Obsolete and removed) (Sufficient, together with H74: Ensuring that opening and closing tags are used according to specification and H94: Ensuring that elements do not contain duplicate attributes when used with Ensuring that Web pages can be parsed by using one of the following techniques:).


The objective of this technique is to avoid key errors that are known to cause problems for assistive technologies when they are trying to parse content that has the same id attribute on different elements. These errors can be avoided by making sure the Web page does not have duplicate id values. This can be done manually or by using HTML's mechanism to specify the technology and technology version, and validating the document for this condition. There are several validators that the developer can use; validation reports generally mention this type of error. The document type declaration is not strictly necessary for this type of evaluation, but specifying the document type declaration makes it easier to use a validator.


Example 1: HTML Validators

HTML pages include a document type declaration (sometimes referred to as !DOCTYPE statement). The developer can use offline or online validators (see Resources below) to check that id attributes values are only used once on a page. The W3C validador, for example, will report ID "X already defined" when it encounters the second use of an id value.

Other sources

No endorsement implied.

For other resources, see G134: Validating Web pages.



  1. Check that all id attribute values are unique on the web page.

Expected Results

  • Check 1 is true.

Test Rules

The following are Test Rules related to this Technique. It is not necessary to use these particular Test Rules to check for conformance with WCAG, but they are defined and approved test methods. For information on using Test Rules, see Understanding Test Rules for WCAG Success Criteria.

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