Like something written in prison? (6)

I believe the answer is:

penned

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'written in prison?' is the definition.
'penned' can be an answer for 'written' ('pen' can be a synonym of 'write'). I'm unsure of the 'in prison?' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for penned that I've seen before include "Wrote; enclosed" , "in Reading Gaol, perhaps" , "Wrote; confined" , "Put down" , "under house arrest?" .)

I've seen this clue in The Telegraph.

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