Act in a documentary piece? (4)

I believe the answer is:

deed

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'act' is the definition.
(I know that act can be written as deed)

I don't understand the remainder of the clue.

(Other definitions for deed that I've seen before include "What's done" , "Something done" , "A conscious action" , "Legal document for transfer of property" , "Heroic exploit" .)

I've seen this clue in the Evening Standard.

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