docs: def has_mixture(val: Any) -> bool:
      """Returns whether the value has a mixture representation.
  
      Returns:
          If `val` has a `_has_mixture_` method and its result is not
          NotImplemented, that result is returned. Otherwise, if the value
          has a `_mixture_` method return True if that has a non-default value.
          Returns False if neither function exists.
      """
      getter = getattr(val, '_has_mixture_', None)
      result = NotImplemented if getter is None else getter()
      if result is not NotImplemented:
          return result
  
      # No _has_mixture_ function, use _mixture_ instead
      return mixture(val, None) is not None