Web Design in a Nutshell, 3rd Edition

Well-Formed XHTML

Web browsers are forgiving of sloppy HTML, but XHTML (being an XML application) requires that you play by the rigid rules of XML markup syntax. What makes XHTML documents different from HTML documents is that you need to be absolutely sure that your document follows the syntax rules of XML correctly (in other words, that it is well-formed ). The sections below summarize the requirements of well-formed XHTML as well as some tips for backward compatibility with older browsers.