Amongst the new features squarely targeted at application developers, HTML 5 introduces a number of new Javascript APIs. These can be used in conjunction with corresponding HTML elements and include:
- A 2D drawing API which can be used with a new canvas element for rendering graphs, game graphics, or other visual images on the fly.
- An API that allows a web application to register itself for certain protocols or MIME types.
- An API that introduces a new caching mechanism to support off-line web applications.
- An API for playing video and audio which can be used with the new video and audio elements.
- A history API that exposes the browsing history and allows pages to add to it to facilitate better back-button support in AJAX applications.
- Cross-document messaging which provides a means by which documents can communicate with each other regardless of their source domain, in a way designed to prevent cross-site scripting attacks.
- A drag & drop API to use in combination with a draggable attribute.
- An editing API to use in conjunction with a new global contenteditable attribute.
- A new network API to enable web applications to communicate with each other on local area networks, and to maintain bidirectional communications with their originating server.
- Client-side persistent storage with JavaScript APIs for key/value pairs and support for embedded SQL databases.
- Server-sent events in combination with the new event-source element which will facilitate persistent connections to remote data sources and largely eliminate the need for polling in web applications.
A number of new presentation elements have also been introduced with support for familiar page components such as headers, footers, figures, dialog (used to mark-up a conversation), and navigation. There is a new datagrid element which will support interactive tables and trees, a datalist element for combo boxes, and a progress attribute which represents the completion of a long running task. Support for RSS feeds within the page markup has also been added.
For forms the input element's type attribute has new support for dates, times, emails and URLs, so that the browser can provide the user interface elements, for example a calendar date picker or integration with the user's address book, and submit the data in a defined format to the server.
HTML 5 also drops support for some well-know features. The most notable is support for frames, which have long been considered detrimental to accessibility and usability. It should be noted that dropped features will continue to be supported by browsers that also fully support the HTML 5 standard, since support for legacy versions of HTML will remain for many years.
The development of HTML 5 is being stewarded by the W3C's HTML Working Group, founded in March 2007. The group operates entirely in public with nearly 500 participants including members from Apple, Google, IBM, Microsoft, Mozilla Foundation, Nokia and Opera.
"HTML is of course a very important standard," said Tim Berners-Lee, author of the first version of HTML and W3C Director. "I am glad to see that the community of developers, including browser vendors, is working together to create the best possible path for the Web. To integrate the input of so many people is hard work, as is the challenge of balancing stability with innovation, pragmatism with idealism."
HTML 5 will eventually supersede HTML 4 but the finalisation of the specification is still quite some way off. The current plan is to have it available in a preliminary candidate recommendation form in the middle of 2009 and as a formal, final recommendation by September 2010.