Sheets of cloud included in illustration (6)

I believe the answer is:

strati

'sheets of cloud' is the definition.
(plural of 'stratus', type of cloud)

'included in illustration' is the wordplay.
'included in' says the answer is hidden in the clue.
'STRATI' can be found hidden inside 'illustration'.

(Another definition for strati that I've seen is " Grey layer clouds".)

I've seen this clue in The Times.

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