old_contents: from __future__ import unicode_literals
  
  from ..base import Resource
  
  
  class Document(Resource):
      _resource_name = 'documents'
      _is_listable = False
  
      _as_is_fields = ['id', 'href', 'mime_type', 'content', 'type', 'audience']
      _date_time_fields_utc = ['date_created']
      _resource_fields = [
          ('booking', 'Booking'),
      ]
  
  
  class Invoice(Resource):
      _resource_name = 'invoices'
      _is_listable = False
  
      _as_is_fields = ['id', 'href']
      _date_time_fields_utc = ['date_created']
      _resource_fields = [
          ('document', Document),
          ('booking', 'Booking'),
      ]
  
new_contents: from __future__ import unicode_literals
  
  from ..base import Resource
  
  
  class Document(Resource):
      _resource_name = 'documents'
      _is_listable = False
  
      _as_is_fields = ['id', 'href', 'mime_type', 'content', 'type', 'audience']
      _date_time_fields_utc = ['date_created']
      _resource_fields = [
          ('booking', 'Booking'),
      ]
  
  
  class Invoice(Resource):
      _resource_name = 'invoices'
      _is_listable = False
  
      _as_is_fields = ['id', 'href', 'audience']
      _date_time_fields_utc = ['date_created']
      _resource_fields = [
          ('document', Document),
          ('booking', 'Booking'),
      ]
  
subject: Add `audience` field back to Invoice resource