Crossword Genius

Essential part of successful wedding: four bars, perhaps (4,9)

Ross

I believe the answer is:

body structure

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

'four bars perhaps' is the definition.
(I know that Royal sign of Aragon is a flag)

'essential part of successful wedding' is the wordplay.
I cannot really see how this works, but
'part' could be 'structure' (structure is a kind of part) and 'structure' is located in the answer.
'of' could be 'o' and 'o' is found within the answer.
This may be the basis of the 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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