The developer can use off-line or online validators (see Resources below) to check the validity of the HTML pages.XHTML, SVG, SMIL and other XML-based documents reference a Document Type Definition (DTD) or other type of XML schema.As you probably know already, it’s important to check and test your Website to help ensure that it looks great and works beautifully regardless of the browser or platform used.Testing a website before launch is one thing that you cannot afford to take lightly.Just like a minor negligence while constructing a building can cost life of millions of residents , the same way a small error left unnoticed can prove to be fatal for your website.
This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, Math ML, etc.
It is often difficult to determine authorship of Web sources, and even if the author is listed, he or she may not always represent him or herself honestly, or he or she may represent opinions as fact.
The responsibility is on the user to evaluate resources effectively.
Unlike similar information found in newspapers or television broadcasts, information available on the Internet is not regulated for quality or accuracy; therefore, it is particularly important for the individual Internet user to evaluate the resource or information.
Keep in mind that almost anyone can publish anything they wish on the Web.