All HTML pages
This technique relates to Success Criterion 4.1.1: Parsing (Sufficient, together with H74: Ensuring that opening and closing tags are used according to specification and H93: Ensuring that id attributes are unique on a Web page as a way to meet an unwritten technique).
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 duplicate attributes on the same element. This can be checked 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 attributes are only used once on an element. The W3C validador, for example, will report "duplicate specification of attribute X" when it encounters the second definition of the same attribute on an element.
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.
- Check that no attribute occurs more than once on any element
- Check 1 is true.