Introduction to HTML5

The web is more a social creation than a technical one. I designed it for a social effect to help people work together and not as a technical toy. The ultimate goal of the Web is to support and improve our weblike existence in the world. We clump into families, associations, and companies. We develop trust across the miles and distrust around the corner. - Sir Tim Berners-Lee, creator of the World Wide Web

HTML5 is the next major revision of the HTML standard superseding HTML 4.01, XHTML 1.0, and XHTML 1.1. HTML5 is a standard for structuring and presenting content on the World Wide Web.

HTML5 is a cooperation between the World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG).

The new standard incorporates features like video playback and drag-and-drop that have been previously dependent on third-party browser plug-ins such as Adobe Flash, Microsoft Silverlight, and Google Gears.
Browser Support

The latest versions of Apple Safari, Google Chrome, Mozilla Firefox, and Opera all support many HTML5 features and Internet Explorer 9.0 will also have support for some HTML5 functionality.
The mobile web browsers that come pre-installed on iPhones, iPads, and Android phones all have excellent support for HTML5.

New Features

HTML5 introduces a number of new elements and attributes that helps in building a modern website. Following are great features introduced in HTML5.

New Semantic Elements: These are like header, footer, and section
Forms 2.0: Improvements to HTML web forms where new attributes have been introduced for input tag
Persistent Local Storage: To achieve without resorting to third-party plugins
WebSocket: A a next generation bidirectional communication technology for web applications
Server Sent Events: HTML5 introduces events which flow from web server to the web browsers and they are called Server Sent Events (SSE)
Canvas: This supports a two dimensional drawing surface that you can program with JavaScript
Audio and Video: You can embed audio or video on your web pages without resorting to third-party plugins
Geolocation: Now visitors can choose to share their physical location with your web application
Microdata: This lets you create your own vocabularies beyond HTML5 and extend your web pages with custom semantics
Drag and drop: Drag and drop the items from one location to another location on a the same webpage

Backward Compatibility

HTML5 is designed, as much as possible, to be backward compatible with existing web browsers. New features build on existing features and allow you to provide fallback content for older browsers.