Bug 93400 LTK UI should provide official API for structural content in the preview page
org.eclipse.ltk.ui.refactoring/src/org/eclipse/ltk/internal/ui/refactoring/PreviewWizardPage.java
private static class NullPreviewer implements IChangePreviewViewer {
		private Label fLabel;
		public void createControl(Composite parent) {
			fLabel= new Label(parent, SWT.CENTER | SWT.FLAT);
			fLabel.setText(RefactoringUIMessages.PreviewWizardPage_no_preview); 
		}
		public void refresh() {
		}
		public Control getControl() {
			return fLabel;
		}
		public void setInput(ChangePreviewViewerInput input) {
		}
	}
	
	private class NextChange extends Action {
		public NextChange() {
			setImageDescriptor(CompareUI.DESC_ETOOL_NEXT);
			setDisabledImageDescriptor(CompareUI.DESC_DTOOL_NEXT);
			setHoverImageDescriptor(CompareUI.DESC_CTOOL_NEXT);
			setToolTipText(RefactoringUIMessages.PreviewWizardPage_next_Change); 
			PlatformUI.getWorkbench().getHelpSystem().setHelp(this, IRefactoringHelpContextIds.NEXT_CHANGE_ACTION);			
		}
		public void run() {
			fTreeViewer.revealNext();	
		}
	}
	
	private class PreviousChange extends Action {