Moving across and inside (5)

I believe the answer is:

astir

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'moving' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for astir that I've seen before include "in the land of the living" , "Excited; out of bed" , "In motion - out of bed" , "Moving; out of bed" , "Up and about -- is art (anag)" .)

I've seen this clue in the Sydney Morning Herald.

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