HTML and XHTML
This technique relates to Success Criterion 4.1.1: Parsing (Sufficient, together with H93: Ensuring that id attributes are unique on a Web page and H94: Ensuring that elements do not contain duplicate attributes 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 which involve having opening and closing tags that are not used according to specification. These errors can be avoided by using the HTML or XHTML mechanism to specify the technology and technology version, and making sure the Web page does not have these types of errors in it. There are several validators that the developer can use: validation reports generally mention these types of errors. This technique deals only with errors related to incorrectly formed opening and closing tags. 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
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 all id attribute values are unique and that opening and closing tags are used according to the specification.
The specification for which elements require closing tags has changed with the introduction of HTML5.
Example 2: XHTML
Like other XML-based documents, XHTML documents reference a Document Type Definition (DTD) or other type of XML schema. The developer can use online or offline validators (including validation tools built into editors) to check that opening and closing tags are used according to the specification.
Example 3: Using test frameworks
When a Website generates HTML or XHTML dynamically instead of serving only static pages, a developer can use XHTMLUnit, XML Test Suite or a similar framework to test the generated XHTML code.
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 there are closing tags for all elements with required closing tags.
- Check that there are no closing tags for all elements where closing tags are forbidden.
- Check that opening and closing tags for all elements are correctly nested.
Steps 1, 2, and 3 are true.