def _detect_multi_byte(self, fb):
        # type: (str) -> bool
        """ _detect_multi_byte returns whether the AbstractUVarIntField is represented on  # noqa: E501
          multiple bytes or not.

          A multibyte representation is indicated by all of the first size bits being set  # noqa: E501

        @param str fb: first byte, as a character.
        @return bool: True if multibyte repr detected, else False.
        @raise AssertionError
        """
        assert(isinstance(fb, int) or len(fb) == 1)
        return (orb(fb) & self._max_value) == self._max_value