Full Form of XHTML:
Extensible Hyper Text Markup Language
XHTML Full Form is Extensible Hyper Text Markup Language. XHTML belongs to the XML languages family that causes the extension of versions of the Hypertext Markup Language (which is known as HTML and is the language that Webpages use). Before HTML5, HTML was defined as being an application of SGML (Standard Generalized Markup Language), XHTML is a more limited subset of the SGML. The XHTML documents are considered well-formed and therefore be easily parsed with the help of standardized XML parsers, which is different from the case of HTML that requires a lenient parser.
XHTML 1.0 in the year 2000 was announced a World Wide Web Consortium (abbreviated as W3C) Recommendation whereas the XHTML 1.1 was announced a W3C Recommendation in the same year after a couple of months. Currently, XHTML5 is under development. XHTML documents are generally backward compatible with the HTML 4 users in those cases where there is adherence to the application guidelines.
XTML 1.1 is compatible however the ruby annotation elements do not form part of the HTML4 Specification and are often ignored by the HTML4 browsers. XHTML 2.0 is comparatively less compatible however, scripting can help reduce this problem significantly. Specifications of HTML and XHTML are inter-compatible when there is strict adherence to the XHTML5 syntax but there still are a few issues relating to this. The aim of XHTML was to increase the extensibility of HTML and interoperability with other kinds of data formats. Development of XHTML is important and therefore, cannot be ignored.