Technique H93:Ensuring that id
attributes are unique on a Web page
Description
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.
Examples
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.
Applicability
All HTML pages
Tests
Procedure
- Check that all id attribute values are unique on the web page.
Expected Results
- Check 1 is true.