In 1998, the W3C (World Wide Web Consortium) decided they would not continue to evolve HTML and froze the standard at HTML 4.01. W3C instead moved forward with XML and the XHTML standard. This new standard, based on XML, required self-closing tags and syntax rule like quoting attributes to name a few.
The XHTML was transitional, meaning you could still get away with using HTML 4.01. The hope was that this would give designers and developers the time to move to the strict XHMTL standard. With this in place W3C began work on XHTML 2.0, which would completely change the language and was not backwards compatible. The consortium thought this new standard was more logical and better designed and in the long run it would be worth the challenges of changing the syntax.
A small group at Opera disagreed. They were convinced that XML was NOT the future of the web. They began work on proof of concept specification that would extend HTML Form Tags without breaking backwards compatibility in late 2003. That spec eventually became Web Forms 2.0.
Others unhappy with the direction of the W3C and XHTML took notice and soon a group from Mozilla and Apple Computers began working on this new specification privately. They formed WHATWG (Web Hypertext Application Technology Working Group) in 2004 led by Ian “Hixie” Hickson from Opera. Hickson moved from Opera to Google in 2005 and continue to work on this new specification called Web Application 1.0.
In 2006 the W3C, under pressure from the software and browser communities, began to realize the they had been overly optimistic in expecting the world to move to XML standard and the HTML Working Group was resurrected.
In 2009, the W3C stopped work on XHTML 2.0, and put all of their resources into HTML5. The philosophies of backwards compatibility, clean design and “not breaking the web” made it clear that HTML5 was the direction to go.
What new in HTML5? Since an increasing number of websites are what we call web applications and not just static content. HTML5 specifications have a new DOM APIs for drag and drop, server-sent events, drawing, video and more.
HTML5 spec went into final draft in October 2009. Support for the new features is continuing to increase as browsers roll out new versions. Compatibility tables for support of HTML5, CSS3, SVG and more in desktop and mobile browsers