XHTML is considered to be the next version of basic HTML. The abbreviation stands for Extensible Hypertext Markup Language. XHTML also has the same applications as HTML but also conforms to XML syntax. HTML is an application of the Standard Generalized Markup Language which is considered as a very flexible markup language while XHTML conforms to XML which is a more restrictive subset of SGML. It can be said that XHTML is the reformulation of HTML for the XML format.

Before, HTML was the only language that website designers use to create website pages. But since then, the World Wide Web has advanced and developed even more which required more powerful tools as well as means to cope up with the new demands that the development brought.

For instance, since the increasing popularity and development of mobile devices now allow it to be connected online, web content may need to use a more complex set of HTML syntax. This is needed in order to provide the same online content targeted for traditional desktop PC's and allow them to be browsed from more resource constricted mobile devices.

The first version of XHTML that came out had minimal differences with HTML. The first version was mainly developed to achieve conformance to XML. One of the more telling changes was that documents must be well-formed and that the elements used must be closed as a requirement of XML. In XML, elements and attributes are case-sensitive which led to XHTML being developed by defining all tag names in the lower case.

The W3C or World Wide Web Consortium, the organization that maintains and develops standards for the World Wide Web has provided the process and guidance on how to publish XHTML documents to be HTML compatible in order for such documents to be served on web browsers that were not designed for XHML.

Most web browsers support for XHTML media types. But one notable web browser that does not support XHTML is the Internet Explorer, one of the world's most popular web browsers. Instead of rendering XHTML media types for viewing, it pops out a dialog box to ask online users to save the content on the hard disk instead.