When IE head Dean Hachamovitch announced the first platform preview of IE 10 at the MIX conference in April he said further preview releases would be "between 8 and 12 weeks apart".
Platform Preview 2 arrives after 11 weeks and adds features for web apps, including Drag-drop and File Reader; so you can drag objects around on a web page - look for a magnetic fridge poetry demo on the IE test drive site soon - or drag files into browser windows to upload them and have that happen in the background.
File access is possibly the first feature from the HTML5 Labs previews to make it into IE.
PP2 also gets the web workers spec. Rob Mauceri, the lead program manager on the IE team, calls that "a popular request from developers" (we count it as the most common request in the IE blog after Flebox, which arrived in PP1) and it's going to make a big difference to the performance of web apps – and maybe your battery life.
Other browsers already support web workers, although Firefox 5 does not allow messages sent through a direct 'channel' between different pieces of background code which Microsoft says explains why PP2 does better than Firefox at its new Bellagio Fountain test drive demo.
FASTER: IE10 gets Web workers after other browsers…
FIREFOX 5: …Microsoft says Firefox is slower at this test because it doesn't have message channels
PP2 is the first browser to support three new performance APIs, including the Page Visibility setting that the Chrome team has been suggesting web sites use to check if a page is in a background or tab or a minimised window.
"If a web app is pinging the server for data it could be doing a lot of work and increasing the cost of running that server, none of which is needed because the window isn't visible to the user," Mauceri explained.
The IE team confirmed that IE10 PP2 is "the same HTML5 engine seen in the recent public "Windows 8" demos". One new feature that would explain the snappiness of the interface reflowing as you change the size of windows is Media Query Listeners; instead of the browser having to check periodically to see if you've changed the window size, changing the size sends a message to the server that it's changed and might need a new layout.
IE10 PP2 is also the first browser to include CSS3 Positioned Floats (a spec Microsoft recently proposed to the W3C) and Rob Mauceri told us this is "part of the bigger picture of where reading is going online, towards a more print-like experience"; once you have a multi-column page flowing through a grid (all standards added in PP1), you want to be able to position a picture and have the columns flow around it – and that could be useful for web app layouts too.
FULL HARDWARE: Using hardware acceleration PP2 shows more fireflies…
CHROME: It might run on XP but Microsoft shows Chrome lagging on this demo
There are also security improvements for embedding content like maps, ads or feeds form social networks in a web page using iframes; these will now run in a sandbox for extra security (again, something Microsoft tools us Firefox 5 doesn't support).
PP2 also adds HTML5 forms and fields that will only accept specific types of information like email addresses or telephone numbers (something Joe Marini first mentioned to us as coming in the Windows Phone version of IE in the Mango update, suggesting that might be a version somewhere between IE9 and IE10).
Mozilla evangelist Chris Blizzard recently told us Firefox is "almost as fast as IE9 and faster in some places" and Mike Belshie of the Chrome team showed background tabs in Chrome running faster than in IE9 at the Velocity conference this month (but using more battery to do it) but it looks like Microsoft is keeping up with performance improvements.
The IE team isn't afraid to point at problems in other browsers either.
COLOURFUL IE10: It's not enough to implement HTML5 if you get it wrong, says Microsoft
A demo titled 'how stuff works' (showing an HTML5 Canvas app that works in Chrome and Firefox but displays the wrong colours) could almost be called 'how IE10 works better'.
OFF-COLOUR FIREFOX: HTML5 is supposed to cope better with pages that aren't quite perfect – Firefox doesn't seem to manage that as well
GREY GOOGLE: Even worse, Chrome gets no colours at all
Although Mauceri diplomatically phrases it as "we've made a lot of progress as an industry but there is still work to do".
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