Routine spotless exterior to retro interior design (9)

I believe the answer is:

procedure

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

'routine' is the definition.
(I know that routine can be written as procedure)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for procedure that I've seen before include "System for accomplishing something" , "Established way of doing something" , "subject of policy" , "Sequence of steps, course of action" , "Particular course of action to achieve a goal" .)

I've seen this clue in the Sydney Morning Herald.

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