Expression block - Gen<Expr> - 4 - (0:0,0)
    Transition span - Gen<None> - [@] - SpanEditHandler;Accepts:None - (0:0,0) - Tokens:1
        CSharpTokenType.Transition;[@];
    Code span - Gen<Expr> - [val] - ImplicitExpressionEditHandler;Accepts:NonWhiteSpace;ImplicitExpression[RTD];K14 - (1:0,1) - Tokens:1
        CSharpTokenType.Identifier;[val];
