Enables or disables field selection and their sort direction, by clicking E3Alarm's column headers at run time. If True, and the header is invisible (please check the ColumnHeader property), when users click the column title, data is sorted using this column as the key. When users click the same column title again, the sort order is reversed, that is, from ascending to descending and vice-versa. When users click it with the SHIFT key pressed, this field is used as a second key. As in the primary key, a second click with SHIFT pressed reverses the sort order of the secondary field.