anchor.diff:      }
     }
   
  +  /// Executes scheduled DOM update - this should be called from the flush phase
     _writeToDom() {
       _classesToUpdate.forEach((String className, bool toBeAdded) {
         toBeAdded
  
positive.code:     _classesToUpdate[className] = false;
    }
  
    // todo(vicb) add tests
    void setAttribute(String attrName, [value = '']) {
      _scheduleDomWrite();
      _attributesToUpdate[attrName] = value == null ? '' : value;
  
negative.code:     _attributesToUpdate[attrName] = _TO_BE_REMOVED;
    }
  
    /// Schedules a DOM write for the next flush phase
    _scheduleDomWrite() {
      if (!_writeScheduled) {
        _writeScheduled = true;
  