Elite anarchists building imaginary projects (7,2,3,3)

I believe the answer is:

castles in the air

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'imaginary projects' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'elite anarchists building' is the wordplay.
'building' indicates an anagram.
'elite'+'anarchists'='eliteanarchists'
'eliteanarchists' anagrammed gives 'CASTLES IN THE AIR'.

Can you help me to learn more?

(Other definitions for castles in the air that I've seen before include "Fancies" , "daydreams" , "Dreams" , "flying fortresses" , "flying rooks" .)

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

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