Internet Explorer 9 Platform Preview 4.0 Was Released

Microsoft released Internet Explorer 9 Platform Preview 4.0.The new version contains IE9 User Agent String, and provides a lot of CSS3, HTML5, and DOM support. The Platform Preview is an early look at the Internet Explorer 9 platform so some features are incomplete, some may change, and some may be added. This document lists features available in the latest Platform Preview and known issues with those features.
Features Available:

CSS3
Selectors (entire module and ::selection)
Namespaces (all except attribute selectors)
Backgrounds & Borders (border-radius)
Color (rgba(), opacity)
DOM Core Namespaces
DOM Range
DOM L2 Events
Event registration and dispatch APIs (addEventListener, removeEventListener, createEvent, dispatchEvent)
Event capture, bubble and target phases
New event objects (Event, UIEvent, MouseEvent, etc.)
DOM L3 Events
CustomEvent, KeyboardEvent, DragEvent interfaces
HTML5 Selection
XHTML Documents
SVG