anchor.diff:      }
     }
   }
  +
  +/**
  + * Annotation describing the relationship between a getter in [EnginePlugin]
  + * and the associated identifier (in '../../plugin/task.dart') which can be
  + * passed to the extension manager to populate it.
  + *
  + * This annotation is not used at runtime; it is used to aid in static analysis
  + * of the task model during development.
  + */
  +class ExtensionPointId {
  +  final String extensionPointId;
  +
  +  const ExtensionPointId(this.extensionPointId);
  +}
  
positive.code:    * Return a list containing all of the contributed analysis error result
     * descriptors for HTML sources.
     */
    List<TaskDescriptor> get htmlErrors => htmlErrorsExtensionPoint.extensions;
  
    /**
  
negative.code:    * Return a list containing all of the contributed analysis error result
     * descriptors for Dart library specific units.
     */
    @ExtensionPointId('DART_ERRORS_FOR_UNIT_EXTENSION_POINT_ID')
    List<TaskDescriptor> get dartErrorsForUnit =>
        dartErrorsForUnitExtensionPoint.extensions;
  
  