in reply to Re^2: Regexp - match if not between [ ]
in thread Regexp - match if not between [ ]

Look-behind is problematic, for the number of digits etc. are not fixed.

Look behinds can still accommodate the task, but it does get pretty unwieldy if the width variation is more than a few characters:

print for split m[
    (?<! Cf )
    (?: (?<! \w\d\d\d ) | (?<! \w\d\d ) | (?<! \w\d ) )
    \.
    (?! [ ^\] ]+ \] )
]x, $s;;

The fox did it[ at 12.23 ] well, Cf. 23 A423.23
 The swallow was even better,

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But it sounds like you've settled on a solution.

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