static synchronized void enableClearBlackboardCommand( final IToolContext context ) {
if (clearEditBlackboardHandler == null) {
clearEditBlackboardHandler = new AbstractHandler(){
public Object execute( ExecutionEvent event ) throws ExecutionException {
Tool tool = ApplicationGIS.getToolManager().getActiveTool();
if (tool instanceof AbstractEditTool) {
EditToolHandler editToolHandler = ((AbstractEditTool) tool).getHandler();
List<Behaviour> behaviours = editToolHandler.getCancelBehaviours();
UndoableComposite compositeCommand = new UndoableComposite();