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
private ISavePolicy fSavePolicy;
	
	private IPropertyChangeListener fPropertyListener;
	
	private GlobalAnnotationModelListener fGlobalAnnotationModelListener;
	/**
	 * Element information of all connected elements with a fake CU.
	 * @since 3.2
	 */
	private final Map fFakeCUInfoMap= new HashMap();
	/**
	 * Constructor
	 */
	public CompilationUnitDocumentProvider() {
		IDocumentProvider provider= new TextFileDocumentProvider();
		provider= new ForwardingDocumentProvider(IJavaPartitions.JAVA_PARTITIONING, new JavaDocumentSetupParticipant(), provider);
		setParentDocumentProvider(provider);
		fGlobalAnnotationModelListener= new GlobalAnnotationModelListener();
		fPropertyListener= new IPropertyChangeListener() {
			public void propertyChange(PropertyChangeEvent event) {
				if (HANDLE_TEMPORARY_PROBLEMS.equals(event.getProperty()))
					enableHandlingTemporaryProblems();
			}
		};
		JavaPlugin.getDefault().getPreferenceStore().addPropertyChangeListener(fPropertyListener);
	}
	/**
	 * Creates a compilation unit from the given file.
	 *
	 * @param file the file from which to create the compilation unit