Your right. I should have added a little more whitespace to clarify things :)

$re = qr[
    (
        the   (?{ $rep = 'The' })
    |
        quick (?{ $rep = 'Quick' })
    |
        brown (?{ $rep = 'Brown' })
    |
        fox   (?{ $rep = 'Fox' })
    )
]x;
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