Validating Web pages

Important Information about Techniques

See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.1 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.1.

Applicability

Any markup languages and many other technologies.

This technique relates to Success Criterion 4.1.1: Parsing (Sufficient).

Description

The objective of this technique is to avoid ambiguities in Web pages that often result from code that does not validate against formal specifications. Each technology's mechanism to specify the technology and technology version is used, and the Web page is validated against the formal specification of that technology. If a validator for that technology is available, the developer can use it.

Validation will usually eliminate ambiguities (and more) because an essential step in validation is to check for proper use of that technology's markup (in a markup language) or code (in other technologies). Validation does not necessarily check for full conformance with a specification but it is the best means for automatically checking content against its specification.

Examples

Example 1: Validating HTML

HTML pages include a document type declaration (sometimes referred to as !DOCTYPE statement) and are valid according to the HTML version specified by the document type declaration. The developer can use off-line or online validators (see Resources below) to check the validity of the HTML pages.

Example 2: Validating XML

XHTML, SVG, SMIL and other XML-based documents reference a Document Type Definition (DTD) or other type of XML schema. The developer can use online or off-line validators (including validation tools built into editors) to check the validity of the XML documents.

Example 3: Batch validation with Ant

The xmlvalidate task of Apache Ant can be used for batch validation of XML files. The following Apache Ant target is a simple example for the validation of files with the extension .xml in the directory dev\\Web (relative to the Ant build file).

              
              <target name="validate-xml"> 
                <xmlvalidate lenient="no"> 
                <fileset dir="dev/web" includes="*.xml" /> 
                </xmlvalidate> 
              </target>
            

Resources

Resources are for information purposes only, no endorsement implied.

Validating HTML and XHTML

Validating XML

Note that many programming editors, XML editors and integrated development environments (IDEs) can validate XML files. These include the following free and/or open-source tools:

Tests

Procedure

For HTML, SGML-based and XML-based technologies:

  1. Load each page or document into a validating parser.
  2. Check that no validation errors are found.

For other technologies:

Follow the validation procedure defined for the technology in use, if any exists.

Expected Results

For HTML, SGML-based and XML-based technologies:

Step 2 is true.