XHTML (Extensible Hypertext Markup Language) is "a reformulation of HTML4.0 as an application of the Extensible Markup Language (XML)." For readers unacquainted with either term, HTML is the set of codes (that's the "markup language") that a writer puts into a document to make it displayable on the World Wide Web. HTML4 is the current version of it. XML is a structured set of rules for how one might define any kind of to be shared on the Web. It's called an "extensible" markup language because anyone can invent a particular set of markup for a particular purpose and as long as everyone uses it (the writer and an application program at the receiver's end), it can be adapted and used for many purposes - including, as it happens, describing the appearance of a Web page. That being the case, it seemed desirable to reframe HTML in terms of XML. The result is XHTML, a particular application of XML for "expressing" Web pages.

HTML5

HTML5 is the next revision of the Hypertext Markup Language (HTML), the standard programming language for describing the contents and appearance of Web pages. HTML5 was adopted by the new HTML working group of the World Wide Web Consortium (W3C) in 2007. This group published the first public draft of HTML5 in January 2008, but refinements are expected to continue for several years before HTML5 becomes a formal recommendation.

HTML5 is expected to offer numerous improvements over HTML4, including:

• New parsing rules for enhanced flexibility
• New attributes
• Elimination of outmoded or redundant attributes
• Immediate-mode drawing
• Drag and drop
• Back button management
• Timed media playback
• Offline editing
• Messaging enhancements
• Detailed rules for parsing
• MIME and protocol handler registration

HTML Tags

An HTML tag is a special piece of tag that tells a web browser how to display things to the reader HTML tags can be used to changed font sized and color, make text bold and italic, add pictures to your text, add lists and many other things.

When a web browser reads a HTML tag, It doesn’t display it –Its only reads it as an instructions.