What is xhtml?

HTML is rapidly being replaced by XHTML. The differences are very minor, but the results of switching can be worth the effort. The primary benefit is that XHTML is more widely accepted in non "computer" devices like cell phone, palm devices and other scaled down browsers. This is commonly called portability between devices.

XHTML is also said to be extensible, which is the fancy way of saying the new tags can be added without a new document type declaration.

XHTML is not a programming language but rather a markup language like HTML. The primary difference is that XHTML documents must be valid XML, which enforces a strict style of marking up pages which, in theory, makes it a lot easier for web browsers to display pages consistently.

XHTML hasn't caught on as much as its creators would have liked, and hasn't been very successful at replacing badly-written and ugly HTML 4 Transitional on the vast majority of the web. It's no longer seen as the sole successor of HTML 4 and the HTML 5 standard is now expected to dominate (of course, predictions over how technology will evolve are almost always completely wrong and it's probably just as likely that HTML 5 will fail too and something new and unexpected will come along in 5 years)

XHTML stands for extensible hypertext markup language. it is a mid-transition between html and xml (extended markup language). it requires a more strict organisation of the code (for example, every tag should be closed) and it is more cross-browser compliant.

most of the content-management systems available on the net at the moment (blog engines, etc.) use xhtml as generated code.

http://www.w3.org/TR/xhtml1/

or

http://www.w3.org/TR/xhtml1/#xhtml