Expression block - Gen<Expr> - 9 - (0:0,0)
    Transition span - Gen<None> - [@] - SpanEditHandler;Accepts:None - (0:0,0) - Symbols:1
        CSharpSymbolType.Transition;[@];
    Code span - Gen<Expr> - [val?[-1]] - ImplicitExpressionEditHandler;Accepts:NonWhiteSpace;ImplicitExpression[RTD];K14 - (1:0,1) - Symbols:6
        CSharpSymbolType.Identifier;[val];
        CSharpSymbolType.QuestionMark;[?];
        CSharpSymbolType.LeftBracket;[[];
        CSharpSymbolType.Minus;[-];
        CSharpSymbolType.IntegerLiteral;[1];
        CSharpSymbolType.RightBracket;[]];
