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
* Creates a fake compilation unit.
	 *
	 * @param element the element
	 * @param setContents tells whether to read and set the contents to the new CU
	 * @since 3.2
	 */
	private ICompilationUnit createFakeCompiltationUnit(Object element, boolean setContents) {
		if (!(element instanceof IStorageEditorInput))
			return null;
		
		final IStorageEditorInput sei= (IStorageEditorInput)element;
		
		try {
			final IStorage storage= sei.getStorage();
			IJavaModel jm= JavaCore.create(ResourcesPlugin.getWorkspace().getRoot());
			IJavaProject jp;
			
			jp= jm.getJavaProject("__projectWorkingcopy__"); 
			IPackageFragmentRoot root= jp.getPackageFragmentRoot(jp.getProject());
			IPackageFragment pkg= root.getPackageFragment(""); 
			ICompilationUnit cu= pkg.getCompilationUnit(storage.getName());
			
			WorkingCopyOwner woc= new WorkingCopyOwner() {
				/*
				 * @see org.eclipse.jdt.core.WorkingCopyOwner#createBuffer(org.eclipse.jdt.core.ICompilationUnit)
				 * @since 3.2
				 */
				public IBuffer createBuffer(ICompilationUnit workingCopy) {
					return new DocumentAdapter(workingCopy, storage.getFullPath());
				}