Doris on shift confined to building (7)

I believe the answer is:

indoors

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'confined to building' is the definition.
I can't tell whether this definition defines the answer.

'doris on shift' is the wordplay.
'shift' is an anagram indicator.
'doris'+'on'='dorison'
'dorison' is an anagram of 'INDOORS'.

Can you help me to learn more?

(Other definitions for indoors that I've seen before include "home" , "not the place for outsiders?" , "Within house" , "Covered" , "Inside a building" .)

I've seen this clue in The Globe and Mail.

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