XHTML Black Magic: W3C DTD
If you wish to become an XHTML wizard you must first master the art of the Document Type Definition (DTD). This simple line of code is almost always forgotten and hardly understood by HTML beginners.
A DTD does exactly what it says: define a type of document. Basically it’s a link to a definition file somewhere on the web, most typically the W3C (the folks who come up with web standard guidelines to begin with), that has a bunch of information about the way you’ve marked your document.
