code: def granular_markings_circular_refs(instance):
      
      if instance['type'] != 'marking-definition':
          return
  
      if 'granular_markings' in instance:
          for marking in instance['granular_markings']:
              if 'marking_ref' in marking and marking['marking_ref'] == instance['id']:
                  yield JSONError("`granular_markings` cannot contain any "
                                  "references to this marking definition object"
                                  " (no circular references).", instance['id'])
docs: Ensure that marking definitions do not contain circular references (ie.
      they do not reference themselves in the `granular_markings` property).