Crossword Genius

In jail, as Bach was? (6,4)

Ross

I believe the answer is:

behind bars

I'm a little stuck... Click here to teach me more about this clue!

'in jail' is the definition.
(I've seen this before)

'as bach was?' is the wordplay.
I cannot really see how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for behind bars that I've seen before include "Where drinks are kept" , "Incarcerated" , "tapsters" , "Where alcohol is kept" , "Where landlords might be" .)

I've seen this clue in The Independent.
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