Regular dairies need a certain acreage (4)

I believe the answer is:

area

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'certain acreage' is the definition.
'area' can be an answer for 'acreage' (I've seen this in another clue). I am not sure about the 'certain' bit.

'regular dairies need a' is the wordplay.
'regular' indicates alternate letters.
'need' means one lot of letters go next to another.
The alternate letters of 'dairies' are 'are'.
'are'+'a'='AREA'

Can you help me to learn more?

(Other definitions for area that I've seen before include "District; locale" , "topic" , "Space occupied by something" , "Expanse or neighbourhood" , "Region, space" .)

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

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