Species charge

def charge(self):
        """Species charge"""
        if self._reader._level == 3:
            # Look for FBC charge
            for ns in (FBC_V2, FBC_V1):
                charge = self._root.get(_tag('charge', ns))
                if charge is not None:
                    return self._parse_charge_string(charge)
        else:
            charge = self._root.get('charge')
            if charge is not None:
                return self._parse_charge_string(charge)

        return None