anchor.diff:      return RetentionPriority.LOW;
     }
   }
  +
   
   /**
    * Recursively visits [HtmlUnit] and every embedded [Expression].
  
positive.code:       return true;
      }
      return source.exists();
    }
  
    @override
  
negative.code:   }
  }
  
  class _ElementByIdFinder extends GeneralizingElementVisitor {
    final int _id;
    Element result;
  
    _ElementByIdFinder(this._id);
  
    @override
    visitElement(Element element) {
      if (element.id == _id) {
        result = element;
        throw new _ElementByIdFinderException();
      }
      super.visitElement(element);
    }
  }
  
  class _ElementByIdFinderException {
  }
  
  class _PolymerHtmlUnitBuilder_findTagDartElement extends
      RecursiveElementVisitor<Object> {
    final PolymerHtmlUnitBuilder PolymerHtmlUnitBuilder_this;
  