public override VisualBasicSyntaxNode VisitAttributeTargetSpecifier(CSS.AttributeTargetSpecifierSyntax node)
            {
                SyntaxToken id;

                switch (node.Identifier.CSKind())
                {
                case CS.SyntaxKind.AssemblyKeyword:
                    id = SyntaxFactory.Token(SyntaxKind.AssemblyKeyword);
                    break;

                case CS.SyntaxKind.ReturnKeyword:
                    // not necessary, return attributes are moved by ConvertAndSplitAttributes.
                    return(null);

                default:
                    throw new NotSupportedException();
                }
                return(SyntaxFactory.AttributeTarget(id));
            }