. . . 1). 0 Strict in this case, and the URL of its DTD. Next comes the html line which indicates the default XML name space used. An important advantage of XHTML is the ability to use tags defined in other name spaces. These three initial lines tell browsers how to process the document. In most situations, you can use the above template verbatim for creating your HTML files.
An Introduction to Web Design and Programming by Paul S. Wang