public  void clear()

 public ColumnSort getColumnSort(String columnId)
Identifies how (or if) a column is sorted.

 public List<SortConstraint> getSortConstraints()
Returns a list of sort constraints, identifying which columns are sorted, and how.  May return an empty list (but
won't return null).

 public  void updateSort(String columnId)
Updates the column sort.  The receiver determines how to handle the sort request.