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

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.

Resources are for information purposes only, no endorsement implied.

• Do not forget to add a doctype by the W3C Quality Assurance Initiative explains what doctypes are and why you should use them.

• Recommended DTDs to use in your Web document by the W3C Quality Assurance Initiative is a list of commonly used declarations.

• How do I validate my code or check for possible errors? describes the tools in the free editor HTML-Kit for checking HTML, CSS and XML.

For other resources, see G134: Validating Web pages.

Procedure

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

Expected Results

• Check 1 is true.

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.