Expression block - Gen<Expr> - 15 - (0:0,0)
    Transition span - Gen<None> - [@] - SpanEditHandler;Accepts:None - (0:0,0) - Tokens:1
        SyntaxKind.Transition;[@];
    Code span - Gen<Expr> - [val?[abc]?[def] - ImplicitExpressionEditHandler;Accepts:Any;ImplicitExpression[RTD];K14 - (1:0,1) - Tokens:8
        SyntaxKind.Identifier;[val];
        SyntaxKind.QuestionMark;[?];
        SyntaxKind.LeftBracket;[[];
        SyntaxKind.Identifier;[abc];
        SyntaxKind.RightBracket;[]];
        SyntaxKind.QuestionMark;[?];
        SyntaxKind.LeftBracket;[[];
        SyntaxKind.Identifier;[def];
