What is XHTML ?

XHTML was developed to make HTML more extensible and increase interoperability with other data formats.HTML 4 was ostensibly an application of Standard Generalized Markup Language (SGML); however the specification for SGML was complex, and neither web browsers nor the HTML 4 Recommendation were fully conformant to it. The XML standard, approved in 1998, provided a simpler data format closer in simplicity to HTML 4.

By shifting to an XML format, it was hoped HTML would become compatible with common XML tools; servers and proxies would be able to transform content, as necessary, for constrained devices such as mobile phones.

Overview

By utilizing namespaces, XHTML documents could provide extensibility by including fragments from other XML-based languages such as Scalable Vector Graphics and MathML. Finally, the renewed work would provide an opportunity to divide HTML into reusable components (XHTML Modularization) and clean up untidy parts of the language.