Performances: when they're extraordinary, they're secret? (10)

I believe the answer is:

renditions

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

'performances' is the definition.
(rendition is a kind of performance)

'when they're extraordinary they're secret?' is the wordplay.
I cannot really understand how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is present in the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.

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