e4 Renderer based on the Xcss language which is part of the Xtext project (see http://www.xtext.org)

The implementation is contained in the bundle fragment org.eclipse.e4.ui.css.swt.theme.xcss.
However, we had to copy the host bundle and remove the OSGi service registration for 
pragmentic reasons: It was simply not possible to supersede the entry in the thememanager.xml.
If we find a bulletproof way to shadow the service registration from the outside, we'll 
be pleased to do so.