Validating web pages
Here are some reasons they mentioned: While contemporary Web browsers do an increasingly good job of parsing even the worst HTML “tag soup”, some errors are not always caught gracefully.
Very often, different software on different platforms will not handle errors in a similar fashion, making it extremely difficult to apply style or layout consistently.
Even if you can, do you want to risk being on the wrong side of a lawsuit if your site proves inaccessible to - for instance - a disabled person who cannot use a 'conventional' browser? Whilst validation doesn't guarantee accessibility (there is no substitute for common sense), it should be an important component of exercising "due diligence".
It is now just over a year since a court first awarded damages to a blind user against the owners of a website he found inaccessible (Maguire vs SOCOG, August 2000).
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?
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.
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.
Validation is one of the simplest ways to check whether a page is built in accordance with Web standards, and provides one of the most reliable guarantee that future Web platforms will handle it as designed.
It is reasonable to consider that standards such as HTML and CSS are a form of “coding style” which is globally agreed upon.
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.