See also: Internet | HTML | XML
From the w3.org XHTML Overview Page (http://www.w3.org/2002/Talks/www2002-xhtml/Overview.html):
The Extensible HyperText Markup Language (XHTML): the successor of HTML as a family of XML modules
XHTML is not the name of a single, monolithic markup language, but the name of a family of document types (called XHTML Family) which collectively form this markup language
The XHTML namespace is identified by the URI http://www.w3.org/1999/xhtml which is shared across XHTML Family members
TakeDown.NET -> “XHTML”