The index is evaluated with any SortDescriptions or Filter being set on this CollectionView.
///
/// If the underlying SourceCollection only implements IBindingList,
/// then only one sort criteria in form of a
/// Classes like ADO's DataView (the view around a DataTable) do implement
/// IBindingListView which can support sorting by more than one property
/// and also filtering
/// Some IBindingList implementations do not support sorting; for those this property
/// will return an empty and immutable / read-only SortDescription collection.
/// Attempting to modify such a collection will cause NotSupportedException.
/// Use