anchor.diff:      registry.addFunctionDeclaration(this, visitor);
       registry.addFunctionTypeAlias(this, visitor);
       registry.addGenericTypeAlias(this, visitor);
  -    registry.addLibraryDirective(this, visitor);
       registry.addMethodDeclaration(this, visitor);
       registry.addMixinDeclaration(this, visitor);
       registry.addTopLevelVariableDeclaration(this, visitor);
  
positive.code:   }
  
    @override
    void visitLibraryDirective(LibraryDirective node) {
      checkComment(node.documentationComment);
    }
  
    @override
    void visitMethodDeclaration(MethodDeclaration node) {
      checkComment(node.documentationComment);
    }
  
negative.code:     final visitor = _Visitor(this);
      registry.addClassDeclaration(this, visitor);
      registry.addClassTypeAlias(this, visitor);
      registry.addCompilationUnit(this, visitor);
      registry.addConstructorDeclaration(this, visitor);
      registry.addEnumConstantDeclaration(this, visitor);
      registry.addEnumDeclaration(this, visitor);
  