Expression block - Gen<Expr> - 19 - (0:0,0)
    Transition span - Gen<None> - [@] - SpanEditHandler;Accepts:None - (0:0,0) - Tokens:1
        CSharpTokenType.Transition;[@];
    Code span - Gen<Expr> - [val?[null ?? true]] - ImplicitExpressionEditHandler;Accepts:NonWhiteSpace;ImplicitExpression[RTD];K14 - (1:0,1) - Tokens:9
        CSharpTokenType.Identifier;[val];
        CSharpTokenType.QuestionMark;[?];
        CSharpTokenType.LeftBracket;[[];
        CSharpTokenType.Keyword;[null];
        CSharpTokenType.WhiteSpace;[ ];
        CSharpTokenType.NullCoalesce;[??];
        CSharpTokenType.WhiteSpace;[ ];
        CSharpTokenType.Keyword;[true];
        CSharpTokenType.RightBracket;[]];
