俱舍論疏 20.135

20.135

論「若無色繫至皆容緣故」，准前色界加無色苦、集所斷，由斯成十。言容緣者，此容有不緣，非決定緣。

The Śāstra says: "If bound to the formless realm […] because all are admitted to take them as objects." By analogy with the previous form realm, adding those of the formless realm abandoned by seeing suffering and origination, ten are thereby constituted. The phrase "admitted to take them as objects" means that they are permitted not to take them as objects; it is not definitive that they must take them as objects.