I am writing here from the Circulation statistics perspective. But the same holds for other (reporting) forms where we want to filter by callnumbers. In our data we have callnumbers starting with three or four digits. (Yes, it would be an idea to add a left zero.) These callnumbers are just alphanumeric. But as human user, the first three or four digits just make you feel that they are numeric. Especially when you enter only those numbers in the callnumber range of Circulation statistics. But when I am looking for e.g. checkouts in a period for callnumbers between 400 and 1000, I wont find any data. Why? Simply because 1000 is smaller than 400. Yes, alphanumeric. But not intuitive as this point. Could we use cn_sort here and perhaps adjust Generic or add a new ClassSortRoutine that pads the numeric first part here to some parametrized length ? What do you think?