IE9 Mobile used in Windows Phone 7.5 Mango used to score 95/100 in the Acid 3 web technology compliance test, but overnight the score has increased to a full 100/100.
The reason is not due to a stealth upgrade, but due to the authors of the test modifying it to remove outdated elements of the test that have been deprecated.
Writing on Google Plus Ian Hickson said:
As the Web matures, we have made a concerted effort to improve the precision of Web technology specifications. It started with CSS 2.1, and then we really ramped things up with the new HTML spec, and now we have broadened the effort to include core DOM features, including DOM Events, DOM Range, and related APIs.
As part of this, we’re trying to simplify parts of the platform that
still haven’t received broad use; for example: changing how exceptions in the aforementioned DOM Range specification work, by merging them into the regular DOMException mechanism; making Attr objects not be Node objects; possibly dropping or simplifying SVG Fonts and SVG SMIL animation; dropping XLink; making DocType nodes work more like other nodes rather than being special.This impacts the Acid3 test, which tested a lot of these APIs in an effort to improve the quality of their implementations so that authors can actually use them. So today, +HÃ¥kon Wium Lie and I are announcing that we have updated the Acid3 test by commenting out the parts of the test that might get changed in the specs, including everything I listed above. We hope this will allow the specs to change in whatever way is best for the Web, rather than constraining the changes to only be things that happened to fit what Acid3 tested!
Note that since some browsers have so far avoided implementing some of these areas (because they are likely to change, and browser vendors don’t want to implement them only to change them again), especially the SVG parts, commenting out some of these tests does result in some browsers’ results improving, in some cases all the way to a full pass.
While the Acid3 test is now pretty old, the change is very relevant when it comes to HTML5, where the IE9 browser performs well, but does not score as high as other browsers. Microsoft has always maintained the standard is still in flux, and that it was pointless to support features which are in fact not even standardized yet, just to get a few brownie points on an arbitrary test. In the end it is about being able to render a site well, not just about a number.
Via Vladimir Yuneva Blog on MSDN.