Custom Sort function allows you to specify a bespoke custom sort order when a column is sorted (in place of the default alphabetical or numbered sort).
This is ideal for columns where the default sort order doesnt make sense (e.g. a 'Ratings' or 'Tenor' column) where you will want to provide a standard non-alphabetical sort.
It is also suitable for columns where some users might have their own preferred non standard sort (e.g. a 'Sector' column).
You can provide a hard-coded, sorted list of values which will be used to sort the column when the header is clicked (e.g. in the 'Contact' column below).
Or you can provide a function that's evaluated each time sort is run (it receives the cell value and the rest of the row). We use this function to sort the Employee column by surname.