請觀音經疏闡義鈔 2.25

2.25

「重空觀」者，以中道正觀，空生死之有、空涅槃之無，名重空觀也。

Regarding “The contemplation of twofold emptiness”: using the correct contemplation of the middle way, emptying the existence of saṃsāra and emptying the non-existence of nirvāṇa, is called the contemplation of twofold emptiness.