Get id of reaction or species element.

        In old levels the name is used as the id. This method returns the
        correct attribute depending on the level.

def _element_get_id(self, element):
        """Get id of reaction or species element.

        In old levels the name is used as the id. This method returns the
        correct attribute depending on the level.
        """
        if self._reader._level > 1:
            entry_id = element.get('id')
        else:
            entry_id = element.get('name')
        return entry_id