XHTML/History of XHTML

XHTML 1.0
This was the first XHTML standard to be released. It was created to redesign HTML 4.0 to act more like an XML file. To make the change from HTML 4.0 to XHTML 1.0, there was three standards: strict, transitional and frameset. XHTML has the capability to be used with XML files and applications that work with XML files.
 * Strict was the standard that accepted the full XHTML standard.
 * Transitional was used by developers to either make it easier to migrate over from HTML 4.0 or to allow certain standards from HTML version 4.01 Transitional in the XHTML file.
 * Framset was very simply the standard that allowed frames in the XHTML file.

XHTML 1.1
XHTML 1.0 was made with the intention of allowing developers to move from HTML standards to XHTML standards more easily.

XHTML 2.0
XHTML 2.0 was drafted between August 2002 and July 2006. It was designed to supersede HTML 4.0 and XHTML 1.1. In July 2009, World Wide Web Consortium announced plans to discontinue work on XHTML 2.0 by the end of the year in order to focus its effort on HTML 5. HTML 5 is expected to include a XML scheme in place of XHTML 2.0 currently called XHTML 5.

XHTML 5.0
Broadly similar to HTML5.