code: def _migrate_subresources(parent, migrations):
      
      for subresource, resource_migrations in migrations.items():
          parent = _migrate_subresource(
              subresource,
              parent,
              resource_migrations
          )
  
      return parent
docs: Migrate a resource's subresources
  
      :param parent: the parent perch.Document instance
      :param migrations: the migrations for a resource