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In prison, I drag around some­thing to keep me warm (8)

Ross

I believe the answer is:

cardigan

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'something to keep me warm' is the definition.
I can't tell whether this definition defines the answer.

'in prison i drag around' is the wordplay.
'in' indicates putting letters inside.
'prison' becomes 'can' (the can is American slang for prison).
'around' indicates anagramming the letters.
'i'+'drag'='idrag'
'idrag' is an anagram of 'rdiga'.
'can' placed around 'rdiga' is 'CARDIGAN'.

Can you help me to learn more?

(Other definitions for cardigan that I've seen before include "Man in charge" , "Woollen jacket" , "Knitted sweater - Welsh Bay" , "town in Wales" , "Noble officer" .)

I've seen this clue in The Guardian.
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