Everything in show would be superficial (3)

I believe the answer is:

all

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'everything' is the definition.
(all things)

I can't explain the remainder of the clue.

(Other definitions for all that I've seen before include "The whole quantity" , "and 16 Across and 23 Across: Even so" , "nothing more" , "Very nearly" , "Garden path (Fr.)" .)

I've seen this clue in the Evening Standard.

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