type ReferenceEnthalpy = enumeration(zeroAt0K "Enthalpy at 0 K and p0 is 0 (if no additional offset)", zeroAt25degC "Enthalpy at 25 degC and p0 is 0 (if no additional offset)", enthalpyOfFormationAt25degC "Enthalpy at 25 degC and p0 is enthalpy of formation at 25 degC and p0 (if no additional offset)");