The internet has only become a successful universal system because of its standards. These standards define how web servers communicate with web browsers, and the HTML language that they both use.
Web standards are formulated and defined by the World-Wide Web Consortium (or W3C). The standards are very detailed, and are designed so that any standards-compliant web browser will display a standards-compliant web page in the same way.
It is perfectly possible to write web pages that do not conform to the W3C standards, but that look good in one or two particular browsers. The problem is that the pages may well not look the same in other browsers, which may have different methods for “fixing” non-standard pages.
Fonant checks all its pages using the W3C's HTML Validator to ensure that the HTML we use is valid. This check also catches any typing mistakes introduced into the HTML markup.