The KeepHidden argument should keep/drop only hidden columns with the same names as ones that are specified in the arguments. Currently, in the "drop" mode of the transform, it drops all hidden columns, no matter what their name is.

I am not sure this argument should even be relevant for drop mode, I think it should automatically drop all columns with the specified names, whether they are hidden or not.

cc @Zruty0 , @singlis, what do you think?