パラメータ
- rowStart
 - First row in the sort range.
 - rowCount
 - Number of rows in the sort range.
 - comparer
 - An System.Collections.IComparer object that compares Row objects.
 
The System.Collections.IComparer interface has a single method called System.Collections.IComparer.Compare(System.Object,System.Object) that takes two objects as arguments (in this case, they will be Row objects) and returns -1, 0, or +1. For more details, see the documentation for System.Collections.IComparer.
Custom sorting can only be used when the grid is in unbound mode.