The Eclipse 4 Application Platform (E4AP), for the most part, is very similar to the Eclipse 3.x Application Platform. That is, all of JDT and PDE, and most of the Platform, are the same bits as in Eclipse 3.x. The E4AP differs from the Eclipse 3.x platform in the implementation of the Workbench (i.e. the org.eclipse.ui.workbench plugin), and the technologies this new implementation is based on. Before the release, the technologies (modeled UI, dependency injection and service-based programming model, CSS-based styling) were called 'e4' but we are now referring to them as the Eclipse 4 Application Platform. On top of the Eclipse 4 Application Platform, the 4.0 Workbench offers an implementation of the 3.x Workbench APIs, called the compatibility layer, to provide backwards compatibility for existing well-behaved Eclipse 3.x applications.