anchor.diff:        obj.build();
   
         switch (_mode) {
  -        case TimelineMode.SEQUENCE:
  +        case TimelineMode.sequence:
             num tDelay = duration;
             duration += obj.fullDuration;
             obj.delay += tDelay;
             break;
   
  -        case TimelineMode.PARALLEL:
  +        case TimelineMode.parallel:
             duration = Math.max(duration, obj.fullDuration);
             break;
         }
  
positive.code:           "You can't push anything to a timeline once it is started");
      Timeline tl = _pool.get();
      tl._parent = _current;
      tl._mode = TimelineMode.PARALLEL;
      _current._children.add(tl);
      _current = tl;
    }
  
negative.code: }
  
  class TimelineMode {
    static const int sequence = 1, parallel = 2;
  }
  