Where the rank and file come from? (7,6)

I believe the answer is:

private source

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'where' is the definition.
I know nothing about this answer so I can't tell whether this works.

'rank and file come from?' is the wordplay.
I cannot quite see how this works, but
'rank' could be 'private' (I've seen this before) and 'private' is located in the answer.
'from?' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
This explanation may well be incorrect...

'the' is the link.

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

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