code: def titles2marc(self, key, values):
      
      first, rest = values[0], values[1:]
  
      self.setdefault('245', []).append({
          'a': first.get('title'),
          'b': first.get('subtitle'),
          '9': first.get('source'),
      })
  
      return [
          {
              'a': value.get('title'),
              'b': value.get('subtitle'),
              '9': value.get('source'),
          } for value in rest
      ]
docs: Populate the ``246`` MARC field.
  
      Also populates the ``245`` MARC field through side effects.