code: def accumulate_from_superclasses(cls, propname):
      ''' Traverse the class hierarchy and accumulate the special sets of names
      ``MetaHasProps`` stores on classes:
  
      Args:
          name (str) : name of the special attribute to collect.
  
              Typically meaningful values are: ``__container_props__``,
              ``__properties__``, ``__properties_with_refs__``
  
      '''
      cachename = "__cached_all" + propname
      # we MUST use cls.__dict__ NOT hasattr(). hasattr() would also look at base
      # classes, and the cache must be separate for each class
      if cachename not in cls.__dict__:
          s = set()
          for c in inspect.getmro(cls):
              if issubclass(c, HasProps) and hasattr(c, propname):
                  base = getattr(c, propname)
                  s.update(base)
          setattr(cls, cachename, s)
      return cls.__dict__[cachenamef accumulate_from_superclasses(cls, propname):
      ''' Traverse the class hierarchy and accumulate the special sets of names
      ``MetaHasProps`` stores on classes:
  
      Args:
          name (str) : name of the special attribute to collect.
  
              Typically meaningful values are: ``__container_props__``,
              ``__properties__``, ``__properties_with_refs__``
  
      '''
      cachename = "__cached_all" + propname
      # we MUST use cls.__dict__ NOT hasattr(). hasattr() would also look at base
      # classes, and the cache must be separate for each class
      if cachename not in cls.__dict__:
          s = set()
          for c in inspect.getmro(cls):
              if issubclass(c, HasProps) and hasattr(c, propname):
                  base = getattr(c, propname)
                  s.update(base)
          setattr(cls, cachename, s)
      return cls.__dict__[cachename]
docs: Traverse the class hierarchy and accumulate the special sets of names
      ``MetaHasProps`` stores on classes:
  
      Args:
          name (str) : name of the special attribute to collect.
  
              Typically meaningful values are: ``__container_props__``,
              ``__properties__``, ``__properties_with_refs__``