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