Writing Valid HTML and XHTML

If you write HTML correctly, you're almost there.

XHTML is an instance of XML. It's this relationship to XML that makes XHTML a powerful markup language.

XHTML documents can be processed by XML-enabled software. They are accessible to an increasing number of tools that take advantage of XML to read, re-write, and search documents.

XHTML can be used in conjunction with other instances of XML, like Mathematical Markup Language.

XHTML documents can be read by alternative platforms less powerful than desktop computers and less tolerant than computer-based browsers: the list already includes portals, voice readers and Braille printers, PDAs, & digital TVs.

Because they are accessible, XHTML documents help the Library comply with U.S. laws and accessibility guidelines.