大乘百法明門論開宗義決 1.139

1.139

能起合離非二欲者。釋前起愛為業言也。此中欲者即是愛故。謂領順境而起合欲。領違境相而起離欲。領俱非境起非二欲。非二欲者即是非合離欲也。

Regarding 'Being able to give rise to desire for conjunction, separation, and neither': this explains the earlier statement that 'giving rise to desire is its function.' 'Desire' here is precisely attachment. This means that experiencing a concordant object gives rise to the desire for conjunction; experiencing a discordant object gives rise to the desire for separation; and experiencing an object that is neither gives rise to a desire for neither. 'A desire for neither' refers to a desire that is neither conjunction nor separation.