俱舍論頌疏論本 1.62

1.62

此中空無礙者，釋虛空體。此中者，於略所說三無為中，虛空但以無礙為性。由無障故，色於中行。

"Here, space is unobstructed" explains the substance of space (ākāśa). "Here" means among the three unconditioned factors briefly mentioned, space merely has non-obstruction as its nature. Because there is no hindrance, matter moves within it.