setCommand(new ModelDrivenCommand() {
@Override
public void execute(Dialog dialog, Object data) {
// activate target unit
QName targetId = (QName)data;
// 1.) verify activation constraints
assert getRuntimeAPI().canBeActivated(targetId) : "Unit is not activatable: "+ targetId;
String suffix = targetId.getSuffix();
boolean isRelative = suffix !=null && (suffix.equals("prev")||suffix.equals("next"));
InteractionUnit unit = dialog.findUnit(targetId);
if(isRelative)
coordinator.getDialogState().activateBranch(unit, suffix);