XHTML Basics

An optional XML Prolog giving version and encoding information
- Encoding is assumed to be UTF-8 or UTF-16 if not declared
XML Document Type Definition stating what type of document it is

An html root element containing a head element followed by a body element

<?xml version="1.0" encoding="iso-8859-1" ?> Optional
<!DOCTYPE html  PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"  XHTML Strict
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
  <head>
  ......
  </head>
  <body>
  ......
  </body>
</html>

A valid XHTML document is one that has a DOCTYPE declaration and conforms to the Document Type Definition (DTD) specified
Optionally defines the unique public identifier for the DTD
The system identifier tells the XML parser where the DTD file can be found. Could be a local URL.
Browsers usually recognise document type from the public or system identifier without downloading the DTD.

Comments can appear in an XHTML document. They are enclosed by:

                  <!-- This is a comment -->