The Extensible Hypertext Markup Language (XHTML) is a markup language that combines the benefits of HTML and XML. In 1991, the World Wide Web was launched as a document service for the Internet: a range of markup languages have been created by the World Wide Web Consortium (W3C), so that developers can create standardised content for the World Wide Web.
The first markup language created for the World Wide Web was the Hypertext Markup Language (HTML). The Extensible Markup Language (XML) was released in 1998, with the belief it would replace HTML: due to it's openness, simplicity, self description, and extensibility. XML allows users to define their own tags and create rules for those tags: making it far less restrictive than HTML, which uses a standard set of tags and rules.
The problem was that small and medium web developers were accustomed to designing their web content in HTML, and converting their content into a new markup languages was a complex task. Therefore, XML's adoption was not as high as it was expected to be, and it did not replace HTML as the primary markup language used on the World Wide Web. Additionally, when XML was released, not all browsers had built-in XML parsing tools.
Therefore, the World Wide Web Consortium (W3C) decided to develop a compromise: which was the Extensible Hypertext Markup Language (XHTML). XHTML would be an application of XML, but would retain the characteristics of HTML: W3C described XHTML as reformulating HTML in XML. W3C has stated that XHTML is the 'next step' in the evolution of the World Wide Web and the Internet: providing the benefits of XML with the backwards compatibility of HTML.
XHTML was released on the 26th of January, 2000; the following versions of XHTML have been released:
The development of XHTML by the World Wide Web Consortium (W3C) was abandoned in 2009-2010: this was due to the development of HTML5. Independently of the W3C, the Web Hypertext Application Technology Working Group (WHATWG) was founded in 2004: this group included important browser software vendors. The members of WHATWG were disappointed that no new versions of HTML were being developed, and that the W3C was focusing all it's resources on developing XML and XHTML.
WHATWG began to develop HTML5 in 2005, and the HTML working group of W3C officially recognised HTML5 in 2007. HTML5 would support XML, XHTML and HTML: attempting to develop a single markup language for the World Wide Web. HTML5 was released in 2014, and it is still being developed as a collaboration between WHATWG and W3C. XHTML 2.0 was abandoned as an independent markup language in 2009-2010.