We’ve come a long way from the flat documents that made up the Web in its early years. As Internet access has expanded and bandwidth has increased, designers and programmers have figured out ways to build sophisticated, interactive applications that run through the browser. Nowadays, these include Web-based word processors, photo-editing software, money-management tools, and much more.

The next generation of HTML, the markup language that is used to build most Web content, promises to make Web applications work even better. Some proposed features of this new standard–HTML 5–are already being built into several popular browsers, offering a glimpse of an application-enabled Web.

As things stand, Web applications are hampered by the code used to build them because they were never designed to make fullfledged desktop-style programs run. For example, most browsers can only run one piece of JavaScript code–a scripting language that can run on top of HTML–at any one time, and this limits the functionality of a Web application. To make matters worse, different browsers react differently to existing Web standards, leaving developers to struggle to make sure that their application is compatible with different browsers.

“We started to see a migration to doing more and more stuff on the Web,” says Christopher Blizzard, open-source evangelist for the Mozilla Foundation, which maintains the Firefox browser. Blizzard says that most browsers simply cannot access data stored offline, or perform complex graphical capabilities without the use of a plug-in such as Flash or Java. “We’re trying to find ways for people to be able to take the live, programmable documents that make up the Web and start integrating them with all these other pieces outside the scope of the browser.”

But guided by HTML 5, browsers are finally being reengineered to address many of these problems. Michael Smith, a member of the World Wide Web Consortium’s HTML working group, says that the most important part of the effort has been creating specifications to ensure that different browsers perform more tasks in the same way.

To help browsers handle intensive Web applications, HTML 5 includes a feature called worker threads. These allow a browser to deal with heavier computation by running JavaScript in the background, while a user goes on interacting with the application as usual. This part of HTML 5 will be supported in the next release of Firefox, and a similar technology is already part of the Google Chrome browser. Brian Rakowski, director of product management for Chrome, says that Google’s browser will move toward the technology described in HTML 5.