The W3C Markup Validation Service | Search for a title, author or keyword | ||||||||
The W3C Markup Validation Service This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc. The World Wide Web Consortium ( W3C ) creates the WWW standards. Most Web documents are written using markup languages, such as HTML or XHTML. These languages are defined by technical specifications, which usually include a machine-readable formal grammar ( and vocabulary ). The act of checking a document against these constraints is called validation, and this is what the Markup Validator does. 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. In the past, many authors who relied on the quirks of Netscape 1.1 suddenly found their pages appeared totally blank in Netscape 2.0. In practice, different browsers can and do display the same page very differently. This is deliberate, and doesn't imply any kind of browser bug. A term sometimes used for this is WYSINWOG - What You See Is Not What Others Get ( unless by coincidence ). 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? Accessibility is the law in many countries. 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 ). 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. One of the important maxims of computer programming is: "Be conservative in what you produce; be liberal in what you accept". Browsers follow the second half of this maxim by accepting Web pages and trying to display them even if they're not legal HTML. Usually this means that the browser will try to make educated guesses about what you probably meant. The problem is that different browsers ( or even different versions of the same browser ) will make different guesses about the same illegal construct; worse, if your HTML is really pathological, the browser could get hopelessly confused and produce a mangled mess, or even crash. That's why you want to follow the first half of the maxim by making sure your pages are legal HTML. The best way to do that is by running your documents through one or more HTML validators.
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