Bug 96917 [implementation] If two editors use the 2.x-compatible API, one or both doesn't work
At least one problem is that 3.0 installs partitioners for every editor that might possibly edit a file, but each editor expects its own partitioner to be installed. Leading to the famous white screen with blue line.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitDocumentProvider.java
FileInfo info= super.createFileInfo(element);
		if (!(info instanceof CompilationUnitInfo))
			return null;
		
		if (original == null)
			original= createFakeCompiltationUnit(element, false);
		if (original == null)
			return null;
		CompilationUnitInfo cuInfo= (CompilationUnitInfo) info;
		setUpSynchronization(cuInfo);
		IProblemRequestor requestor= cuInfo.fModel instanceof IProblemRequestor ? (IProblemRequestor) cuInfo.fModel : null;
		if (requestor instanceof IProblemRequestorExtension) {
			IProblemRequestorExtension extension= (IProblemRequestorExtension) requestor;
			extension.setIsActive(false);
			extension.setIsHandlingTemporaryProblems(isHandlingTemporaryProblems());
		}
		if (JavaModelUtil.isPrimary(original))
			original.becomeWorkingCopy(requestor, getProgressMonitor());
		cuInfo.fCopy= original;
		if (cuInfo.fModel instanceof CompilationUnitAnnotationModel)   {
			CompilationUnitAnnotationModel model= (CompilationUnitAnnotationModel) cuInfo.fModel;
			model.setCompilationUnit(cuInfo.fCopy);
		}
		if (cuInfo.fModel != null)
			cuInfo.fModel.addAnnotationModelListener(fGlobalAnnotationModelListener);
		return cuInfo;
	}
	
	/**