anchor.diff:  import 'selection_model.dart';
   
   typedef bool IsIndeterminate(var entity);
  -
  -/// Count getter to return when there is no valid count
  -final CountGetter _noCountGetter = () => -1;
   
   /// Selection model interface that is meant to be used with the table view
   /// component.
  
positive.code: 
    @override
    bool get isPageSelected =>
        supportsSelectAll &&
        selectedCount > 0 &&
        selectedCount == entitiesOnPageCount();
  
    @override
    void onRemove(T entity) {
  
negative.code:   @override
    SelectableGetter<T> getSelectable;
  
    /// If the table supports selection over multiple pages.
    bool supportsMultiplePageSelection;
  
  