The world is developing too fast and there are many reasons for its rapid development the main reason is the new things appearing in the computer, restless search is taking place in inventing new languages so once it is approved by the people then within no time the other one is appearing. HTML5 is a technology developed by the WHATWG, it is a open community started by four major browser vendors these vendors are Mozilla, opera and apple, this HTML5 is not the replacement of HTML 4.01 or XHTML, it is an evolution, the aims of it are big it tries
"HTML5 (also sometimes referred to as Web Applications 1.0) is a technology developed by the WHATWG, an open community started by three of the four major browser vendors: Mozilla, Opera, and Apple. HTML5 is not so much a replacement for HTML 4.01 or XHTML 1.0 as it is an upgrade or evolution. It aims for backwards compatibility, tries to remove undefined behavior in HTML 4.01 by defining it, and looks at the various browsers’ tag-soup parsing behavior to try to define the best solution that doesn’t break the web. At the same time, it adds sorely
Validation is a process of checking your documents against a formal Standard, such as those published by the Worldwide Web Consortium (W3C) for HTML and XML-derived Web document types, or by the WapForum for WML, etc. It serves a similar purpose to spellchecking and proofreading for grammar and syntax, but is much more precise and reliable than any of those processes because it is dealing with precisely-specified machine languages, not with nebulously-defined human natural language.
It is important to note that validation has a very precise meaning.