code: def short_title(self, key, value):
      
      short_title = value.get('a')
      title_variants = self.get('title_variants', [])
  
      if value.get('u'):
          short_title = value.get('u')
          title_variants.append(value.get('a'))
  
      self['title_variants'] = title_variants
      return short_title
docs: Populate the ``short_title`` key.
  
      Also populates the ``title_variants`` key through side effects.