XHTML (Extensible Hypertext Markup Language) is a part of the family of XML markup languages. It mirrors or extends versions of the widely used Hypertext Markup Language (HTML), the language in which web pages are formulated. While HTML, prior to HTML5, was defined as an application of Standard Generalized Markup Language (SGML), a flexible markup language framework, XHTML is an application of XML, a more restrictive subset of SGML. Because it is XML-based, XHTML can be parsed using standard XML parsers—unlike HTML, which requires a lenient HTML-specific parser. XHTML essentially bridges the HTML and the web standards in a format that can be read and understood by today’s XML-capable web browsers. Think of XHTML as a hybrid car that follows stricter environmental rules than regular cars but can perform much the same functions.
