微軟今天公布了IE9 Platform PReview4，新版包含IE9 User Agent String，終于可以不再被服務器端識別為IE8，并提供了大量CSS3、HTML5和DOM的支持。
之前IE9公發布了三個技術預覽版，分別提供了GPU渲染和新的JS引擎，并且微軟正計劃對IE9進行更多改變，使其全面支持W3C的Web標準，包括 HTML5, SVG 1.1第二版, CSS3媒體查詢, CSS3邊框與背景, CSS3選擇器, DOM level 3核心, DOM level 3事件和DOM level 2風格。

What's new in Internet Explorer 9 Platform Preview 2 1.9.7766.6000:
Features Available:
- IE9 User Agent String
- getElementsByClassName
- characterSet
- CSS3 Media Queries
- HTML5 Events
- DOMContentLoaded
- DOM Core
- DocumentType, ProcessingInstruction, createDocument
- DOM Traversal
- DOM L3 Events
- DOMAttrModified, Composition events

Features Partially Implemented :
- DataURI
- Support in script source

Developer Tools Features Available :
- User Agent String Picker
- A new tool that can be used to change the user agent string that IE sends with every request. The tool comes with some built in presets and new custom user agent strings can be added.
- Console Tab
- The console window is now a full tab and has been expanded to include the logging of diagnostic information from IE.
- Network inspection improvements
- Shortened URL
- Color coding for errors
- Scaling units (eg. 500 ms becomes 0.5 s)