I can't point to the docs, but it's parenthesis do not affect scope only precedence. There could be some exceptions, but that's generally how I think about it. E.g.,

(my $line); # scoped outside of `while` block
while ($line = <>) {

}
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or

while (my $line = <>) { # $line scoped only inside of `while` block

}
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Treating my in a distributive way inside the parens shows your implicit understanding. I think. :-)