If set to false, the user will not be able to sort the data, otherwise it will depend on the clicked column settings.

The first time the user click the column header the data will be sorted in ascending order, and the second time in descending order. if the Ctrl key is pressed while the user clicks the column header the sorting state of the others column will be preserved, otherwise the current column sort criteria will override the previous sorting state.

Reference

C1DataGrid Class
C1DataGrid Members