docs: def get_mixedins_by_name(target):
          """Get a set of couple (name, field) of target mixedin."""
  
          result = getattr(target, Mixin.__MIXEDIN_KEY__, None)
  
          if result is None:
              result = dict()
              setattr(target, Mixin.__MIXEDIN_KEY__, result)
  
          return result