Mobile Web Programming has a detailed writeup of the new HTML5 and W3C future standards support included in yesterday's iOS 4.2 release. These new APIs haven't been fully documented yet by Apple, but these changes have been uncovered as part of Mobile Web Programming's own independent research. They include new standards like Accelerometer and Gyroscope support in the DeviceOrientation API, the WebSockets API that's part of HTML5, and information on how to invoke printing dialog in mobile Safari.
Not only is Mobile Web Programming's information detailed and informative, the comments to the post are also fairly illuminating. There's a lot more going on in yesterday's iOS 4.2 release than a casual user might suspect, and there's a lot of great news in this release for web developers. If you have any interest in the spinning cogs and gears that make the mobile web work, it's definitely worth your time to check out this writeup. These additions help buttress the idea that Apple is committed to supporting the ongoing growth of HTML5 web standards and the importance of those open standards.