F.4. W3C XHTML Validation Service

Programming Web-based applications can be complex, and XHTML documents must be written correctly to ensure that browsers process them properly. To promote correctly written documents, the World Wide Web Consortium (W3C) provides a validation service (validator.w3.org) for checking a document's syntax. Documents can be validated either from a URL that specifies the location of the file or by uploading a file to the site validator.w3.org/file-upload.html. Uploading a file copies the file from the user's computer to another computer on the Internet. Figure F.2 shows main.html (Fig. F.1) being uploaded for validation. The W3C's Web page indicates that the service name is MarkUp Validation Service, and the validation service is able to validate the syntax of XHTML documents. All the XHTML examples in this book have been validated successfully using validator.w3.org.

Figure F.2. Validating an XHTML document. (Courtesy of World Wide Web Consortium (W3C).)

By clicking Browse..., users can select files on their own computers for upload. After selecting a file, clicking the Validate this file button uploads and validates the file. Figure F.3 shows the results of validating main.html. This document does not contain any syntax errors. If a document does contain syntax errors, the validation service displays error messages describing the errors.

Figure F.3. XHTML validation results. (Courtesy of World Wide Web Consortium (W3C).)