HTML and XHTML are mark up languages.
XHTML stands for Extensible Hyper Text Mark Up Languages while HTML stands for Hyper Text Mark Up Language.
XHTML needs to be properly nested, properly closed, tag names and attributions in lower case and it must have one root element.
XHTML is HTML 4.01 redesigned as XML.
XHTML is currently the most widely used standard for websites on the internet, despite the fact that the new standard, HTML5, is available. XHTML can support different browsers, like Internet Explorer 9, Google Chrome, Mozilla Firefox, Opera and Safari. It can support all browsers run on mobile phone and other similar small devices. Small devices often cannot interpret the bad HTML. XHTML is a family of current and future document types and modules that reproduce, subset, and extend HTML 4.It extends HTML 4 by utilizing Extensible Markup Language (XML), which is a language that is designed to carry data, not display it.By combining HTML with XML it retains the flexibility of HTML but allows for cleaner, well-formed coding. What this means is that a web page can now have dynamic, interactive content as XHTML is actually an XML application.
CHANGES AND UPDATES
Initial website designs normally need small tweaks and changes after they go live, but major updates and re-designs may be undertaken periodically.