anchor.diff:        for (component in iterate(result).by_class()){
           detach(spannerLib.Spanner, component);
         }
  -      if (result is Component){
  +      if (result is this.runtimeType){
           result = [result];
         }
         else {
           result = list(result);
         }
         result = selectionLib.Selection(result);
  -      return result
  +      return result;
     }
   
     _cache_named_children() {
  
positive.code:     return name_dictionary;
    }
  
    /*
      def _copy_with_children_and_indicators_but_without_spanners(self):
          return self._copy_with_indicators_but_without_children_or_spanners()
  
      def _copy_with_indicators_but_without_children_or_spanners(self):
          new = type(self)(*self.__getnewargs__())
          if getattr(self, '_lilypond_grob_name_manager', None) is not None:
              new._lilypond_grob_name_manager = copy.copy(override(self))
          if getattr(self, '_lilypond_setting_name_manager', None) is not None:
              new._lilypond_setting_name_manager = copy.copy(set_(self))
          for indicator in self._get_indicators():
              new_indicator = copy.copy(indicator)
              attach(new_indicator, new)
          return new
  
      def _detach_grace_containers(self, kind=None):
          from abjad.tools import scoretools
          grace_containers = self._get_grace_containers(kind=kind)
  
negative.code: import 'package:abjad/selection.dart' as selectionLib;
  import 'package:abjad/timespan.dart' as timespanLib;
  import 'package:abjad/spanner' as spannerLib;
  import 'package:abjad/utils/utilities.dart' show attach, set_, deatch, iterate, mutate, override;
  import 'package:abjad/abc/AjadOject' show AbjadObject;
  import 'package:abjad/utils/copy' as copy;
  
  
  class Component extends AbjadObject{
  