Validating web pages
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.It is indeed one of the principal strengths of the web, that (for example) a visually impaired user can select very large print or text-to-speech without a publisher having to go to the trouble and expense of preparing a separate edition.Do remember: household-name companies expect people to visit afford that luxury?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.
Indeed, most developers creating rich Web applications know that reliable scripting needs the document to be parsed by User-Agents without any unexpected error, and will make sure that their markup and CSS is validated before creating a rich interactive layer.
This makes validation seem useless or costly to many people, and the following questions (or statement) are widespread: The answer to this one is that markup languages are no more than data formats. It only takes on a visual appearance when it is presented by your browser.
In practice, different browsers can and do display the same page very differently.
XHTML, SVG, SMIL and other XML-based documents reference a Document Type Definition (DTD) or other type of XML schema.
The developer can uses online or off-line validators (including validation tools built into editors) to check the validity of the XML documents.