Format of an HTML document
DTD is the SGML subset definition that tells the browser which version of HTML the document should be read as. (May need to define Standard Generalized Markup Language.) Usually omitted, may be required in future versions of HTML.
HTML container defines the document portion (according to DTD spec)
Header is required (unless document is for a FRAME only; see Advanced HTML course); some older browsers crash without it; contains TITLE information, and document meta-information
Body contains the bulk of the document.
Address (in or out of BODY) contains contact information, possibly copyright notices, and so on. (More on ADDRESS on page 56.)