old_contents: from typing import Tuple  # NOQA
  
  from n0core.model import Model  # NOQA
  
  
  class Target(object):
      """Target is application service to apply resources with some framework like KVM and iproute2.
  
      A target manage only one type `*/*/*` of resource like `resource/network/flat`.
      Directory structure and class name is ruled by resource type.
      For example, `resource/network/flat` define `class Flat` which is placed on `n0core.resource.network.flat`.
      """
  
      def __init__(self):
          # type: () -> None
          pass
  
      def apply(self, model):
          # type: (Model) -> Tuple[Model, bool, str]
          """Apply resource with some framework.
  
          Args:
              model: Model which you want to apply.
  
          Return:
              Tuple of processed model, is_succeeded and description.
          """
          pass
  
new_contents: from typing import Tuple  # NOQA
  
  from n0core.model import Model  # NOQA
  
  
  class Target(object):
      """Target is application service to apply resources with some framework like KVM and iproute2.
  
      A target manage only one type `*/*/*` of resource like `resource/network/flat`.
      Directory structure and class name is ruled by resource type.
      For example, `resource/network/flat` define `class Flat` which is placed on `n0core.resource.network.flat`.
  
      Do not kill resource when target is killed.
      """
  
      def __init__(self):
          # type: () -> None
          pass
  
      def apply(self, model):
          # type: (Model) -> Tuple[Model, bool, str]
          """Apply resource with some framework.
  
          Args:
              model: Model which you want to apply.
  
          Return:
              Tuple of processed model, is_succeeded and description.
          """
          pass
  
subject: add rule about resource liveness.