TOPN in Microsoft Docs wrong documentation ERROR

TOPN is a iterator, it generates a row context based on the second parameter. if the sort by field,ie the third parameter, is one column of the second parameter, then it will reference the field of conresponding row. if you set a field which not belongs to the second parameter, then will get a error, then you need to use a expression of aggregation function or a measure. on this point, you must be careful of context transactions. a measure or a expression using calculate function will automatically transacts all current row context into filter context.